Physical Unit 1.3: Bonding (inc. Shapes)

Question 1

what is the structure of ionic compounds?

Answer 1

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

Question 2

why do ionic compounds have high mp & bp?

Answer 2

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

Question 3

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

Answer 3

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

Question 4

what factors affect the strength of ionic bonds & how?

Answer 4

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)

Question 5

describe the nature of metallic bonding

Answer 5

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

Question 6

what is the structure of metals?

Answer 6

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

Question 7

explain the properties of metals

Answer 7

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

Question 8

what factors affect the strength of metallic bonds & how?

Answer 8

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

Question 9

what is a covalent bond?

Answer 9

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

Question 10

what is a co-ordinate/dative covalent bond?

Answer 10

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

Question 11

what is the structure of simple molecular substances?

Answer 11

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

Question 12

what are the properties of simple molecular substances & explain?

Answer 12

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

Question 13

what is the structure of giant covalent substances?

Answer 13

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

Question 14

do giant covalent substances conduct electricity?

Answer 14

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

Question 15

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

Answer 15

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

Question 16

why is graphite soft & malleable?

Answer 16

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

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

learn table for each # of lone & bonding pairs

Answer 19

.

Question 20

define electronegativity

Answer 20

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

Question 21

what factors affect electronegativity?

Answer 21

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

Question 22

state & explain the trends in en in the periodic table

Answer 22

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

Question 23

why are some covalent bonds non-polar?

Answer 23

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

Question 24

why are some covalent bonds polar?

Answer 24

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

Question 25

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

Answer 25

VDW only

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

Question 26

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

Answer 26

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)

Question 27

state the 3 types of intermolecular forces

Answer 27

Van de Waal’s forces/induced dipole-dipole

permanent dipole-dipole attractions

Hydrogen bonding

Question 28

how do Van de Waal’s forces arise?

Answer 28

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

Question 29

what affects the strength of the VDW forces?

Answer 29

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

Question 30

how do permanent dipole-dipole attractions arise?

Answer 30

exist b/w 2 polar molecules

Question 31

how does hydrogen bonding arise?

Answer 31

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

Question 32

how is H bonding drawn?

Answer 32

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

Question 33

how is mp/bp influenced by IMFs?

Answer 33

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

Question 34

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

Answer 34

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

Question 35

a substance is soluble if

Answer 35

it forms H-bonds with water molecules

Question 36

why does bp increase down a group?

Answer 36

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

Question 37

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

Answer 37

equal repulsion b/w bonding pairs of e-s

Question 38

what is a permanent dipole?

Answer 38

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

Question 39

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

Answer 39

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

Question 40

define polar bond

Answer 40

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