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Chemistry Revision Unit 1

Unit 1
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Properties:
• High melting and boiling point because a lot of energy is required to
break the strong ionic bond
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Metallic Bonding
In metals, the electrons leave the outer shells of metal atoms, forming
positive metal ions and a ‘sea’ of delocalised electrons
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The bond type is
electrostatic attraction force between conduction electrons (in the
form of an electron cloud of delocalized electrons) and positively
charged metal ions
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The charge of the metal ion
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The size of the metal ion
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• Conduct electricity because of the sea of delocalised electrons which
can move through the structure to carry the charge
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Covalent Bonding
A covalent bond forms when two non-metal atoms share a pair of
electrons
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An atom that shares one or more
of its electrons will fill its outer shell
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• Do not conduct electricity because there are no free electrons
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(coordinate bonding is always
polar)

Electronegativity and Bond Polarity
Electronegativity: The power of an atom to attract electrons towards it
itself in a covalent bond
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Li and F’s electronegativity is so different that F would steal Li’s
electrons to form an ionic bond
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Electronegativity and Bond Polarity
In a covalent bond the electron pair is not usually shared exactly evenly
between the two atoms unless they are the same atom or have the
same electronegativity
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Electronegativity and Bond Polarity
Non-polar covalent bond:

Electronegativity and Bond polarity
Polar covalent bond:
A polar covalent bond is formed when the shared pair of electrons in a
covalent bond are not shared equally
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Intermolecular Forces
Intermolecular forces are forces that exist between molecules
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They affect melting and boiling points
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This can cause other molecules to do the same as the electrons
repel and the delta negative and delta positive are attracted
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This uneven distribution of electrons can make one side of the atom more
negatively charged than the other, thus creating a temporary dipole, even on
a non-polar molecule
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g
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A molecule with a permanent dipole moment
is called a polar molecule
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g
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A hydrogen bond is
formed when a charged part of a molecule having polar covalent bonds
forms an electrostatic (charge, as in positive attracted to negative)
interaction with a substance of opposite charge
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Hydrogen Bond
Happens with:
Oxygen:

Nitrogen:

Fluorine:

Lone pair

Hydrogen Bonds
Compounds containing hydrogen:
The boiling points increase as the compound goes down the group
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However this doesn’t apply to H₂O, HF or NH₃
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So H₂O, HF and NH₃ have higher boiling points because they have
hydrogen bonds

Hydrogen Bonds
Ice:
How does ice form:
Molecules are constantly moving because they have energy
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As it cools potential energy decreases and molecules move slower
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Why does ice float:
The formation of hydrogen bonds push the molecule apart
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This reduces the density of ice
compared to water which allows it to float
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g
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5°, e
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H₂O

Trigonal Planar: 3 bond pairs, 0 lone pair, 120°, e
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BF₃
Trigonal Pyramidal: 3 bond pairs, 1 lone pairs, 107°, e
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NH₃

Shapes of Molecules
Tetrahedral: 4 bond pairs, 0 lone pairs, 109
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g
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g

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