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hello this is Dr H ail and this is a
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second part of chemical bonding in which
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we'll be talking about the different
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structures whether they're simple
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molecular structures or giant
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macromolecular structures so let us take
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a look at the difference between these
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two types of structures
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molecular and Joint so what do we mean
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by simple molecular structure simple
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molecular structure is in which we have
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the individual
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molecules separate from each other with
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only weak forces between them for
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example if we say we have water
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molecules each molecule is separate from
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the others but there is very weak
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intermolecular
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forces in inter molecular forces means
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the forces between molecules so if we
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have molecules like the molecules of
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water or molecules of carbon
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dioxide these have weak attraction
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forces between the molecules and as a
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result of that simple molecular
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structures always have low melting point
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now if we say why does anything any
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substance have a low melting point why
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does water carbon dioxide oxygen
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chlorine why do they have low melting
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point this is because of weak attraction
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forces between
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molecules we have weak attraction forces
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between molecules these are called
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intermolecular forces and these need a
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very small amount of energy to be broken
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so we heat it to just a little bit and
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the molecules separate that is what we
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call a low melting point so remember
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most substances have simple molecular
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structures and if they have simple
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molecular structures then they have low
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melting point why do they have low
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melting point because there is weak
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attraction forces between molecules or
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weak
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intermolecular forces that need a small
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amount of energy to be broken to
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separate these molecules so that they
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can either uh melt or they can
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boil so this question says carbon
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dioxide has a low melting point State
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the general term for the weak forces
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that cause carbon dioxide to have a low
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melting point we said molecules like
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carbon dioxide have low melting point
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and we said why do they have low melting
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point we said because they have weak
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attraction forces between molecules now
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what is the general term for the weak
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attraction forces between the molecules
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we call them inter MO molecular
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forces silicon tetrachloride has a low
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melting point because it has weak forces
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of attraction between particles now name
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the type of particles that are held
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together by the weak attraction forces
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so if I tell you that the Silicon
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tetrachloride has weak attraction forces
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between between what between molecules
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so these are the type of particles that
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are held together by these weak forces
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of
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attraction giant macromolecular
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structures are large threedimensional
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structure in which there are many atoms
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strongly bonded together so things or
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substances either have simple molecular
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structure like what we just talked about
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carbon dioxide water chlorine whatever
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or they have giant structures the word
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macromolecular means giant
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threedimensional
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structure in which many atoms are
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strongly bonded together now what
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examples do we have of giant
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macromolecular structures we will talk
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about the structures of ionic crystals
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which we're going to say are called uh
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Crystal Lati the metall structure so
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we're going to talk about the structure
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of metals metals are regarded as
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giant diamond and graphite are giant
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Cove valent structures and silicon
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dioxide also is a giant coent molecule
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so we either have giant ionic or giant
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metallic or giant calent like diamond
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graphite and silicon
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dioxide so an ionic compound what is the
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structure of any ionic compounds we've
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talked about ionic and calent compounds
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most calent compounds have the simple
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molecular
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structures the ionic compounds have a
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giant structure so they are in the form
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of ionic crystal latise in which we have
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giant threedimensional
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structure with regular arrangement of
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alternating positive and negative ions
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so we have when we have sodium chloride
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for example we don't just have one
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sodium next to one chloride ion no we
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have a giant threedimensional structure
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with many many positive negative
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positive negative in a regular
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arrangement of alternating positive and
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negative and that means each positive
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ion will have six negative ions around
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it and each negative ion is surrounded
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by six positive
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on now as a result of
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this what kind of melting point will it
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have it will have high melting point
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we're going to say that all giant
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structures have high melting in point so
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ionic crystals for example they have
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high melting points because they are
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held by strong electrostatic attraction
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forces between the oppositely charged
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ions all these positive negative
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positive negative when we have
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oppositely charged particles they are
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attracted to each other and this kind of
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Attraction is called
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electrostatic attraction forces so in
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the ionic Crystal latise it has a high
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melting point why because there is
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strong electrostatic attraction forces
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between
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what between positive and negative ions
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or between oppositely charged ions so
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this is in the ionic Crystal LTI now
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what about Metals now metals also have a
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giant structure because we said metals
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have regular rows of positive ions
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surrounded by a CA of delocalized
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electrons so if we're going to describe
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the structure of any metal he says
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describe structure of copper or zinc or
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sodium any metal it has giant
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threedimensional
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structure with rows of closely packed
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positive ions
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surrounded by a sea of delocalized
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electrons this is because each atom in a
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metal has one or two or three electrons
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in its outer shell it doesn't want it so
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these outermost electrons are really a
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little bit far away from each atom so
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now they are not atoms they're positive
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ions and the electrons in the outer
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shell are referred to as delocalized
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electrons because
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they can move around these rows of
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positive ions so it is giant
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threedimensional
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structure with what with rows of closely
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packed positive ions because these are
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solids of course so they are all closely
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packed surrounded by a sea of
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delocalized electrons or electrons that
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are free to move now why do metals have
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high melting and boiling points we're
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going to say because of the strong
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electrostatic attraction forces between
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what when we were talking about ionic we
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said between positive and negative ions
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but Metals do not have that metals have
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positive ions and negative
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electrons please pay
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attention so if we say okay if he asks
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for physical properties of all All
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Metals what are the physical properties
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of All Metals please remember all metals
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don't say they are
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hard because some metals are soft don't
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say they have high melting points some
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of them are actually we have a a liquid
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metal at room temperature don't say they
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all have a very high density but what
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applies to all metals is first first of
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all they all conduct electricity All
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Metals conduct electricity and you have
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to remember they conduct electricity
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both as a solid or when molten so as a
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solid or as a liquid All Metals conduct
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electricity now why do they conduct
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electricity due to the presence of free
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moving electrons remember we said what
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was the structure of metals there are
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rows of positive ions surrounded by
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delocalized electron so the fact that it
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has electrons that are free to move that
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is why Metals conduct electricity so if
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we say Metals conduct electricity first
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of all both as a solid and as a
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liquid why because they have free moving
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electrons you should also know that all
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metals are malleable and ductile
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malleable means they can be spread out
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into sheet
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like aluminium foil for example and
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ductile means they can be pulled into
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wires now why are metals malleable and
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docti you should know because the layers
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of positive ions can slide over each
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other when heated or hammered so they
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have layers of positive ions and these
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layers of positive ions can slide over
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each other so all metals can be shaped
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they are malleable and ductile and of
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course all metals are
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shiny so in this question he's saying
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titanium is a metal the diagram shows
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arrangement of particles in titanium
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State why Metals such as titanium are
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good conductors of
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electricity do you remember why is it
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that metals are good conductors of
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electricity because they have de
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delocalized electrons that are free to
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move or they have free moving
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delocalized
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electrons explain why Metals such as
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titanium are malleable again why are
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metals
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malleable layers of positive ions can
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slide over each other when heated or
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H okay another example of
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giant substance this is a giant Co
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valent element diamond is made of carbon
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graphite is also made of carbon so they
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are all elements but they are giant and
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they are calent because we have many
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many atoms coal bonded together so we
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have diamond we have graphite we have
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also a form of carbon which is called
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fine now what is Diamond so diamond we
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said it's a form of carbon so all the
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atoms are carbon but if we're going to
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explain the structure of course we're
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going to say it has a giant
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threedimensional
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structure in which each carbon atom is
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coal bonded to how
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many four other carbons and this kind of
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structure is is called a
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tetrahedral structure so to explain the
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structure of diamond giant
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threedimensional
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structure in which each carbon atom is
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coent bonded to four other carbons in a
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rigid
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tetrahedral
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structure what about graphite we're
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going to describe the structure of
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graphite we're going to say again it's a
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giant threedimensional structure
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in which
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what in which each carbon atom is coal
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bonded to how
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many to three other carbon atoms in
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layers of six-sided rings with weak
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attraction forces between the layers So
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within each layer we have strong calent
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bonds each carbon is covalently bonded
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to three other carbons but this is made
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up of of layers of six-sided rings and
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there are weak attraction forces between
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the
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layers so let's compare between diamond
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and
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graphite you know that we're going to
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say that all of them are forms of corbon
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so they are actually what we call
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allotropes they are different forms of
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the same element so they're different
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forms of carbon we know what diamond is
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and you should know that graphite is is
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for example the substance in your pencil
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that's a graphite okay so what is the uh
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difference between them if we're going
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to talk about which one is hard and
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which one is soft you should know that
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diamond is one of the hardest substances
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that we have why is it hard because of
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its
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structure because of the strong Calum
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bonds between carbon atoms in the rigid
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threedimensional
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tetra hedral structure so this makes it
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hard what about graphite we said
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graphite is soft why is it soft we said
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because there is weak attraction forces
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between the layers that allows them to
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slide past each other or allows the
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layers to slide over each
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other okay what else Diamond does not
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conduct Electric remember we said each
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carbon atom is covalently bonded to four
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other carbon atoms that means each
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carbon is in group four it has four
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electrons in its outer shell when it
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makes four bonds with four other carbons
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it has used up all its electrons so di
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one does not conduct electricity because
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of absence of free electrons it doesn't
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have any free electrons but graphite if
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you remember we said each corbon is
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cently bonded to three carbons carbon
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has four electrons in its outer shell it
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used the only three of them so each
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corbon has one free electron floating
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around so graphite conducts electricity
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because it has free
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moving
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electrons what is the use of each of
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them you should know that diamond is
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used in cutting and drilling equipment
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please don't say diamond is used as
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jewelry we don't say that diamond is
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used in what in cutting and drilling
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equipment why because it's hard why is
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it hard because it has strong coent
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bonds between carbon atoms in the rigid
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threedimensional
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tetrahedral structure so it is hard
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because of its structure now because
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it's hard we use it for what we use it
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for cutting and drilling
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what about graphite well graphite we
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said it's soft so because it is soft I
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can use it as a lubricant or lubricating
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agent now we also said that graphite
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conducts electricity so we can use it as
00:18:15
electrode and we will be talking about
00:18:17
electrodes when we talk about the
00:18:20
chapter on electrolysis so for now know
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that
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graphite is used as an electrode because
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it conducts
00:18:31
electricity so let's take a look at this
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question the lead in a pencil is made of
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a mixture of graphite and Clay when the
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percentage of graphite is increased the
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pencil moves across the paper more
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easily so the fact that we write with a
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pencil is because the graphite
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inside uh moves across the paper now
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Which statement explains why graphite
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moves easily over the paper of course
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it's not because it has high melting
00:19:04
point or because it's a p carbon we said
00:19:08
graphite is a lubricant it's a lubricant
00:19:12
it's soft its layers can slide over each
00:19:15
other because the layers have weak
00:19:18
attraction forces between them which
00:19:21
statement about graphite and diamond is
00:19:23
correct well let's take a look he's
00:19:25
saying Diamond has high melting point
00:19:27
but graphite does not is that
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correct remember that both of them are
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giant so both of them have high melting
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point he says graphite and Diamond both
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conduct electricity which One conducts
00:19:43
electricity graphite conducts
00:19:45
electricity not Diamond graphite and
00:19:48
Diamond both have giant structures yes
00:19:52
both of them are giant macromolecular
00:19:55
structures if he says graphite is ionic
00:19:58
that's wrong graphite is
00:20:02
coent okay another example of a giant
00:20:06
three threedimensional structure is
00:20:08
silicon dioxide so silicon dioxide is a
00:20:12
giant molecule with many many atoms but
00:20:16
here it is made up of silicon and oxygen
00:20:19
atoms so if we are going to describe the
00:20:22
structure of silicon dioxide silicon
00:20:25
dioxide has a giant threedimensional
00:20:28
tetrahedral structure so it has a
00:20:31
structure similar to that of diamond but
00:20:35
here we have each silicon atom is coent
00:20:39
bonded to four oxygen atoms and each
00:20:42
oxygen is bonded to two silicon atoms
00:20:46
this is the structure of silicon dioxide
00:20:50
so if we ask silicon dioxide compared to
00:20:54
carbon dioxide both silicon and carbon
00:20:57
are in the the same group but silicon
00:21:00
dioxide is a solid this is actually what
00:21:03
we call Sand while carbon dioxide is a
00:21:07
gas at room temperature why is that you
00:21:11
should realize that when we talked about
00:21:12
carbon dioxide we said it is made up of
00:21:16
molecules with weak attraction forces
00:21:19
between the molecules while silicon
00:21:22
dioxide we said is a giant
00:21:25
threedimensional
00:21:26
tetrahedral structure
00:21:28
so the fact that silicon dioxide is
00:21:30
solid while carbon dioxide is a gas this
00:21:33
is because carbon dioxide molecules
00:21:36
exist independently with weak attraction
00:21:40
forces between them so the molecules are
00:21:42
separate and they have only weak
00:21:45
attraction forces between the molecules
00:21:48
while silicon dioxide has a giant three
00:21:52
dimensional tetrahedral structure with
00:21:55
many strong calent bonds so this will
00:21:59
need a lot of energy to be broken so it
00:22:02
will have a high melting
00:22:05
point explain in terms of structure and
00:22:08
bonding why silicon dioxide has a high
00:22:12
melting point
00:22:14
again why does silicon dioxide have a
00:22:16
high melting
00:22:18
point because of its structure so
00:22:21
because it has a giant threedimensional
00:22:24
structure with many strong Calum bonds
00:22:28
that need a lot of energy to be
00:22:33
broken if he's asking diamond and
00:22:36
silicon dioxide both have giant
00:22:38
structures which of these statements are
00:22:41
correct well let's look at the
00:22:43
statements he's comparing Diamond to
00:22:46
silicon
00:22:47
dioxide both substances are compounds is
00:22:51
that
00:22:52
right we said diamond is made of what
00:22:56
diamond is made of carbon so actually
00:22:58
diamond is an element silicon dioxide is
00:23:02
made of silicon and oxygen so that's a
00:23:04
compound there are many strong covalent
00:23:07
bonds in Diamond yes that is correct
00:23:10
there are many strong covalent bonds in
00:23:12
Diamond silicon dioxide is bonded
00:23:15
ionically is silicon dioxide an ionic
00:23:20
compound no we said it's a giant coent
00:23:23
just like diamond both substances have
00:23:26
very high Mel points yes because both of
00:23:30
them are giant threedimensional
00:23:32
structures so which one was correct
00:23:36
statements two and
00:23:39
four three statements about Diamond
00:23:42
graphite and silicon dioxide are listed
00:23:44
and which statements are correct so
00:23:47
let's take a look at the statements
00:23:49
diamond and graphite both have giant
00:23:53
calent
00:23:55
structures yes that is correct diamond
00:23:57
and graphite both have giant coent
00:24:00
structures what about the second one in
00:24:03
silicon dioxide silicon and oxygen atoms
00:24:07
are joined together by calent bonds
00:24:10
throughout the whole
00:24:13
structure yes that is correct we said
00:24:15
it's a three-dimensional tetrahedral
00:24:18
structure in which uh this there is
00:24:21
calent bonds between all the atoms so
00:24:24
that is correct diamond and silicon
00:24:27
dioxide have similar
00:24:29
structures yes we said diamond and
00:24:32
silicon dioxide both have giant
00:24:35
threedimensional
00:24:36
tetrahedral structure so actually all
00:24:39
these statements are correct okay
00:24:43
another form of carbon is flines and
00:24:46
filines are made up of 60 carbon atoms
00:24:51
joined together in a structure of
00:24:53
pentagons and hexagons that is arranged
00:24:56
in a sphere so actually this is just a
00:24:59
molecule made of 60 carbon atoms this is
00:25:03
regarded as a simple molecular structure
00:25:06
so this is not a giant structure and as
00:25:09
such they have lower melting point than
00:25:13
graphite this is because they have
00:25:15
simple molecular structure with weak
00:25:18
attraction forces between molecules that
00:25:21
need a small amount of energy to be
00:25:24
broken so just keep in mind that fine is
00:25:27
is a form of carbon just like diamond
00:25:30
and graphite but the difference is
00:25:31
diamond and graphite are giant fine is a
00:25:36
simple molecular structure with weak
00:25:39
attraction forces between molecules so
00:25:42
it would have a lower melting
00:25:46
point so there is a question that says
00:25:50
doctors use C60 fine to deliver
00:25:54
medicines to certain parts of the body
00:25:57
so that the medicine does not damage
00:25:59
other parts of the body so just why C60
00:26:04
fine is suitable for this purpose
00:26:07
remember we said fine is a small
00:26:10
molecule and it's in the form of a
00:26:13
sphere so you can put a medicine inside
00:26:16
the fine and you can inject it into uh
00:26:22
certain parts of the body and that is
00:26:25
okay because ferin are are not reactive
00:26:29
they will not react with the medicine
00:26:32
and it is not toxic so that is useful
00:26:36
for this kind of uh medicinal
00:26:41
purposes what about this other question
00:26:43
he's saying describe in terms of
00:26:46
electrostatic
00:26:47
attractions the bonding between the
00:26:50
atoms in Copper and the bonding between
00:26:54
the atoms in graphite what what did we
00:26:58
say about copper copper is a
00:27:00
metal what kind of
00:27:02
Attraction
00:27:04
forces between the atoms do we have we
00:27:08
said in Copper we have layers
00:27:11
of positive ions because the outermost
00:27:15
electrons are floating around so the
00:27:17
atoms are in the form of positive ions
00:27:20
so the attraction forces that we have in
00:27:23
Copper or in any metal are strong
00:27:26
electrostatic attraction forces between
00:27:29
the positive ions or the positive
00:27:32
nucleus of the atoms and the de
00:27:36
localized negative electrons that are
00:27:38
floating around so that is the
00:27:40
interaction that is holding them
00:27:43
together what about graphite now you
00:27:45
should remember that graphite have Cove
00:27:48
valent bonds what kind of electrostatic
00:27:52
attractions do we have in a coent bond
00:27:56
so you're really actually explaining
00:27:59
coent bonds remember you're not
00:28:01
explaining the attractions between the
00:28:03
layers the calent bonds if you remember
00:28:07
when we were defining calent bonds we
00:28:09
were saying the calent bonds are strong
00:28:12
electrostatic attraction forces between
00:28:15
the positive nuclei of the atoms and the
00:28:19
bonding pairs of electrons in the
00:28:23
covalent
00:28:25
bond Explain how copper conducts
00:28:28
electricity remember copper is a metal
00:28:31
why do metals conduct electricity
00:28:34
because they have
00:28:36
delocalized electrons that are free to
00:28:39
move the C of delocalized electrons are
00:28:43
free to move explain why graphite has a
00:28:47
high melting point well graphite has
00:28:52
this kind of giant threedimensional
00:28:56
structure with strong coent bonds so the
00:28:59
strong covalent bonds between the carbon
00:29:02
atoms in the giant threedimensional
00:29:05
structure so we don't just have a few
00:29:07
bonds we have many many strong covalent
00:29:10
bonds so these need a lot of energy to
00:29:14
be
00:29:16
broken another question says titanium
00:29:19
chloride and titanium oxide are both
00:29:22
calent compounds but titanium chloride
00:29:26
is a liquid
00:29:27
while titanium oxide is a solid with
00:29:30
high melting point so he's saying
00:29:33
titanium chloride has low melting point
00:29:36
titanium oxide has high explain these
00:29:40
properties in terms of the structures so
00:29:43
if I tell you that titanium chloride has
00:29:47
low melting point we said anything with
00:29:51
low melting point has simple molecular
00:29:55
structure with weak attraction action
00:29:57
forces between the molecules that need a
00:30:00
small amount of energy to be broken
00:30:03
while if he tells me that titanium oxide
00:30:06
has high melting point then that means
00:30:09
it has a giant calent structure with
00:30:13
strong coent bonds that need a lot of
00:30:15
energy to be broken so please be able to
00:30:20
apply what we said to any other
00:30:23
examples then this question says the
00:30:26
table shows boiling points of some
00:30:28
compounds containing silicon all of
00:30:30
these compounds are coent they have
00:30:33
coent bonds and again he's saying
00:30:35
silicon Tetra fluoride and silicon Tetra
00:30:38
choride have simple molecular structures
00:30:42
while the silicon dioxide has a giant
00:30:45
calent stretch explain why the boiling
00:30:49
point of silicon Tetra chloride is
00:30:52
greater than the boiling point of
00:30:54
silicon Tetra fluide so if I tell you
00:30:57
that both of them are simple so both of
00:31:00
them have relatively low boiling point
00:31:04
now why would one have lower than the
00:31:07
other if both of them are simple
00:31:09
molecular structures that means that the
00:31:12
one that has higher uh boiling point so
00:31:17
silicon Tetra chloride has higher
00:31:19
boiling point that must mean that the
00:31:22
intermolecular forces or the attraction
00:31:25
forces between mole ules in si I4 is
00:31:30
stronger so both of them are coent both
00:31:34
of them are
00:31:35
simple so both of them have weak
00:31:38
intermolecular forces but if one has
00:31:40
higher boiling point than the other then
00:31:43
the one that has higher boiling point
00:31:45
has stronger intermolecular forces or
00:31:49
stronger attraction forces between
00:31:51
molecules that need more energy to be
00:31:55
broken what if he saying explain why the
00:31:58
boiling point of silicon dioxide is very
00:32:00
much
00:32:02
greater well if it has very high melting
00:32:05
point that is because it has strong
00:32:09
coent bonds in the giant structure that
00:32:13
need much more energy to be broken while
00:32:17
the Silicon tetrachloride has weak inter
00:32:21
molecular
00:32:23
forces and that's the end of this part
00:32:26
of the
00:32:27
chapter uh thank you for
00:32:30
listening
