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A-Level Chemistry > Physical Unit 1.3: Bonding (inc. Shapes) > Flashcards

Physical Unit 1.3: Bonding (inc. Shapes) Flashcards

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1
Q

what is the structure of ionic compounds?

A

giant 3d lattice
+ve & -ve ions
often metal & non-metal
(metal atoms lose electrons & non-metal atoms gain electrons = transfer of electrons)
strong electrostatic forces of attraction b/w oppositely charged ions

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2
Q

why do ionic compounds have high mp & bp?

A

a lot of thermal energy is required to overcome strong electrostatic forces of attraction
b/w oppositely charged ions

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3
Q

why do ionic compounds not conduct electricity when solid but do when molten or aqueous?

A

when solid, ions are held in fixed positions so cannot move
when molten or aqueous, ions are free to move, carrying charge

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4
Q

what factors affect the strength of ionic bonds & how?

A

the greater the charge on the ions, the stronger the ionic bonding

the smaller the ions, the stronger the ionic bonding
(ions get bigger down a group)

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5
Q

describe the nature of metallic bonding

A

within metals
metal atoms lose their outer shell electrons
+ve metal ions surrounded by a sea of free-moving delocalised e-s

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6
Q

what is the structure of metals?

A

giant 3d lattice structure
+ve metal ions surrounded by a sea of free-moving delocalised e-s
+ve metal ions are in layers

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7
Q

explain the properties of metals

A

conduct electricity when solid & molten
delocalised e-s are free to move through the structure, carrying charge

high mp
a lot of thermal energy is needed to overcome the strong force of attraction b/w +ve metal ions & -ve delocalised e-s

soft & malleable
layers of +ve metal ions can slide over each other

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8
Q

what factors affect the strength of metallic bonds & how?

A

the smaller the metal ions
the greater the charge on the ions
& the more delocalised outer shell e-s
the stronger the metallic bonding

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9
Q

what is a covalent bond?

A

shared pair of e-s
attracted to & held b/w the nuclei of 2 non-metal atoms
to form full outer shells

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10
Q

what is a co-ordinate/dative covalent bond?

A

both e-s come from the same species
i.e. one species ‘donates’ 2 e-s
drawn with an –>

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11
Q

what is the structure of simple molecular substances?

A

very strong covalent bonds within molecules
relatively weak intermolecular forces b/w molecules

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12
Q

what are the properties of simple molecular substances & explain?

A

low mp & bp
little thermal energy needed to overcome weak intermolecular forces
often liquids & gases at room temp.

do not conduct electricity
do not have free-moving ions or delocalised e-s

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13
Q

what is the structure of giant covalent substances?

A

diamond
each C atom form 4 covalent bonds to other C atoms
giant covalent lattice

graphite
each C atom forms 3 covalent bonds to other C atoms
C atoms arranged in layers
delocalised e-s are free to move b/w layers

silicon dioxide
alternating silicon & oxygen atoms

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14
Q

do giant covalent substances conduct electricity?

A

diamond - no
does not contain free-moving ions or delocalised e-s

graphite - yes
delocalised e-s are free to move b/w layers, carrying charge

silicon dioxide - no
does not contain free-moving ions or delocalised e-s

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15
Q

why do giant covalent substances have high melting & boiling points?

A

a lot of thermal energy is needed to break the very many very strong covalent bonds b/w atoms

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16
Q

why is graphite soft & malleable?

A

C atoms are arranged in layers, which can easily slide over each other

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17
Q

what is e- pair repulsion theory & how does it determine the shapes of molecules (&ions) & bond angles?

A

e-s repel each other as far as possible
lone pairs repel more than bonding pairs

state:
total # e-s in outer shell of central atom
how many e-s from how many atoms bonded to it so total of 8 e-s in outer shell
# of bonding & lone pairs
shape of molecule
bond angles

18
Q

what are the basic shapes for each # of total e- pairs?

A

2 pairs - linear 180
3 pairs - trigonal planar - 120
4 pairs - tetrahedral 109.5
5 pairs - trigonal bipyramidal 120, 90
6 pairs - octahedral 90

19
Q

learn table for each # of lone & bonding pairs

A

.

20
Q

define electronegativity

A

the power of an atom to attract the 2 electrons
in a covalent bond

21
Q

what factors affect electronegativity?

A

as nuclear charge increases,
more protons
stronger attraction b/w nucleus & bonding pair of e-s

as atomic radius decreases,
e-s are closer to the nucleus
stronger attraction b/w nucleus & bonding pair of e-s

as shielding decreases,
fewer shells of e-s b/w nucleus & bonding pair of e-s
less repulsion
stronger attraction b/w nucleus & bonding pair of e-s

22
Q

state & explain the trends in en in the periodic table

A

en decreases down a group
atomic radius increases
shielding increases
so weaker attraction b/w nucleus & bonding pair of e-s

en increases across a period
atomic radius decreases
number of protons increases
same shielding
so stronger attraction b/w nucleus & bonding pair of e-s

23
Q

why are some covalent bonds non-polar?

A

the 2 atoms in the covalent bond have the same en
so the 2 e-s in the covalent bond are shared equally/equally attracted to each nucleus

24
Q

why are some covalent bonds polar?

A

the 2 atoms in the covalent bond have different en
so the 2e-s are not shared equally
the more en atom attracts the pair of e-s more strongly than the less en atom so gets a greater share of the e-s
e.g H-Cl

25
Q

why are some molecules non-polar & what intermolecular forces do they have?

A

VDW only

contains no polar bonds
or
contains polar bonds but dipole moments cancel out bc the molecule has a symmetrical shape

26
Q

why are some molecules polar & what intermolecular forces do they have?

A

contains polar bonds & dipole moments do not cancel out bc the molecule does not have a symmetrical shape

VDW & dipole-dipole attractions or H-bonds (depending on the molecule)

27
Q

state the 3 types of intermolecular forces

A

Van de Waal’s forces/induced dipole-dipole

permanent dipole-dipole attractions

Hydrogen bonding

28
Q

how do Van de Waal’s forces arise?

A

random e- movement causes uneven e- distribution & creates an instantaneous dipole
this induces a temporary dipole in a neighbouring molecule
the partially -ve part of one molecule is attracted to the partially +ve part of another molecule

weakest IMF

29
Q

what affects the strength of the VDW forces?

A

the bigger the molecule
the more e-s it has
so the stronger the VDWs

linear molecules (as opposed to branched) can pack closer together
greater surface contact area
so stronger VDWs

30
Q

how do permanent dipole-dipole attractions arise?

A

exist b/w 2 polar molecules

31
Q

how does hydrogen bonding arise?

A

H atom is bonded to an F, O or N atom, which are very en
dipole results from difference in en b/w H & F, O, N
strong attraction from lone pair to exposed H nucleus

strongest IMF

32
Q

how is H bonding drawn?

A

dotted line from H to lone pair
180 degrees
show all partial charges

33
Q

how is mp/bp influenced by IMFs?

A

non-polar molecules with VDWs only have lowest mp/bp
bc little thermal energy needed to overcome VDWs b/w molecules
the stronger the VDWs, the higher the mp/bp

substances with VDWs & permanent dipole-dipole attractions have higher mp/bp than VDWs only
bc permanent dipole-dipole is stronger than VDWs
so a lot of thermal energy is needed to overcome them

very big molecules with VDWs only can outweigh the effect of dipole-dipole so may have a higher mp/bp

substances with VDWs & H-bonds have highest mp/bp
bc H-bonds are stronger than VDWs & dipole-dipole
so a lot of thermal energy is needed to overcome them

34
Q

how is mp/bp affected by # of H-bonds formed?

A

the more H-bonds formed to other molecules, the greater the mp/bp

35
Q

a substance is soluble if

A

it forms H-bonds with water molecules

36
Q

why does bp increase down a group?

A

molecules are bigger
so have more e-s
so VDWs b/w molecules are stronger
so more thermal energy needed to overcome them

37
Q

explain the shape of molecules with no lone pairs of e-s

A

equal repulsion b/w bonding pairs of e-s

38
Q

what is a permanent dipole?

A

unequal sharing of electrons
causing a partially +ve side & a partially -ve side

39
Q

why is an HCl molecule (as an e.g.) polar?

A

chlorine is more en than H
e-s are attracted towards Cl atom

40
Q

define polar bond

A

bonding pair of e-s is shared unequally b/w the 2 atoms
there are partial charges on the atoms of the bond

A-Level Chemistry (14 decks)

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