bonding & structure

Question 1

metallic bonding found?

Answer 1

in pure metals (sodium, iron) and in alloys (steel)
-metal atoms lose electrons to form + ions

these ions become surrounded by a sea of delocalised electrons- which binds the structure together.

Question 2

typical metal properties

Answer 2

1) most -solids at room temp with high melting points
2) have high electrical/thermal conductivity
3) are malleable and ductile

Question 3

ionic bonding found?

Answer 3

• in compounds containing metal and non metals

- metals lose electrons to form positive ions and non metals gain electrons to form negative ions

Question 4

properties of ionic compounds?

Answer 4

solids at very high melting points
-soluble- in polar solvents (water)
only conduct electricity when dissolved or molten

Question 5

covalent bonding found?

Answer 5

between non metal atoms

the non metals share outer shell electrons to form a stable structure

Question 6

properties of covalent substances?

Answer 6

usually gases, liquids, or solids with low MP

do not dissolve in water- but do dissolve in non polar solvents

do not conduct electricity

Question 7

metallic bond definition

Answer 7

is the electrostatic force of attraction formed between metal ions in a lattice and the sea of delocalised electrons between them

Question 8

why are metals malleable and ductile?

Answer 8

because of the layers of metal ions that can slide over one another without breaking the metallic bonds.

Question 9

comparing Na, Mg, Al variation in metallic bonding

Answer 9

1) MELTING POINTS increase as u go along:

a) the charges on ions increase from Na+, to Mg2+ etc
b) number of delocalised electrons increases
c) the ions get smaller- therefore closely pack together

2) ELECTRICAL CONDUCTIVITY increases:

because the number of delocalised electrons increases- so more electrons are able to move when PD is applied

Question 10

ionic compounds are stable because?

Answer 10

energy is released when they form.
-metals have low ionisation energies and lose electrons easily

-non metals have exothermic electron affinities and gain E easily

• this means that positive and negative ions can form when metals and non-metals react
• as these ions attract, they become arranged into a giant ionic lattice structure contain billions of IB

Question 11

THE STRENGTH OF IONIC BONDING

the force of attraction between ions in a lattice depends on

Answer 11

a) the charges on the ions:
high charge results in strong ionic bonds

b) the sizes of the ions:
small ions pack together more efficiently and form strong ionic bonds

Question 12

covalent bonding usually leads to the formation of

Answer 12

molecules in non metal atoms

the shared pair of electron is attracted to the nucleus of both atoms and therefore holds them together

Question 13

two types of covalent bonds?

Answer 13

normal and dative covalent bonds

Question 14

Dative covalent bonds?

Answer 14

a dative covalent bond is a shared pair of electrons formed when one atom donates both electrons to the bond

Question 15

dative covalent bonds are also formed when

Answer 15

metals dissolve in water

Question 16

THE STRENGTH OF COVALENT BONDS

why do small atoms produce strong covalent bonds?

Answer 16

because the shared pair of electrons lies close to both nuclei.
-the strength of the covalent bond is measured by how much energy is needed to break it.

Question 17

BONDING IN MOLECULAR IONS

Answer 17

molecular ions are basically molecules which have lost or gained electrons to become stable
-eg. Carbonate ions (CO3,2-)

In dot and cross diagrams, the triangle represents the extra electron gained from sodium.

Question 18

3 types of covalent structures:

Answer 18

1) simple molecules eg. CH4, H20,CO2
2) giant covalent lattices eg. diamond, graphite
3) Polymers eg. poly (ethene), poly (propene)

Question 19

SIMPLE MOLECULAR STRUCTURES;

Answer 19

• have low melting points (liquids, gases at RTP)

-because although covalent bonds inside the molecules are strong, there are only weak forces between the molecules
very little heat energy is needed to break these intermolecular forces.

• DONT CONDUCT AT ALL= BC NO CHARGE

Question 20

GIANT COVALENT LATTICES

Answer 20

all atoms across the whole structure are joined by strong covalent bonds.

therefore are mainly solids with extremely high melting points bc huge amount of energy needed to break the strong covalent bonds

Question 21

GIANT COVALENT LATTICE 2

What is the structure of diamond?

Answer 21

1) each and every C atom is covalently bonded to 4 others
2) does not conduct electricity (no free electrons)
3) pure silicon and silicon dioxide have similar structures to diamond

Question 22

what is graphene?

Answer 22

a single layer of graphite, composed of hexagonally arranged carbon atoms linked together by strong covalent bonds.

uses of graphene:

1) used in touch screen, to make them less brittle
2) is light, flexible and transparent and conducts (electronics)

Question 23

what is the structure of graphite?

Answer 23

each carbon atom has 3 covalent bonds to other carbon atoms in layers

• there are delocalised electrons between the layers which can move and conduct electricity
• feels greasy as weak forces between layers allow them to slide

Question 24

what is a polymer?

Answer 24

1) a long chain molecule made up of many smaller molecules (monomers) joined together.
- the chains themselves are strong as they are made with covalent bonds.
- however there are only weak intermolecular forces between the neighbouring chains and so many polymeric substances have LMP and are stretchy.

Question 25

what is the valence shell electron pair theory ?

what are its rules?

Answer 25

is used to explain why molecules have different shapes.

3 RULES:
1) basic shape arises from the number of electron pairs in the outer (valence) shell of the carbon atom in the molecule.

2) electron pairs repel eachother and therefore move as far apart as possible.
3) lone pairs have a greater repulsive effect than covalent bonding pairs, reducing the angle between any bonds

Question 26

Types of bonding pairs

Answer 26

1) 2 bonding pairs= linear molecule eg. BeCl2
have a 180* angle in between

2) 3 bonding pairs= trigonal planar molecule eg. BCl3
have a 120* angle in between

3) 4 bonding pairs= tetrahedral molecule eg. CH4 and silicon tetrachlroride CCl4

4) 5 bonding pairs= trigonal bipyramidal molecule
eg. PCl5

5) 6 bonding pairs= octahedral molecule eg. SF6
6) 3 bonding pairs + 1 lone pair= trigonal pyramid molecule eg. NH3, PCL3

7) 2 bonding pairs + 2 lone pairs= V-shaped molecule
eg. H20 and SCl2

Question 27

BONDING PAIRS

11) comparing methane, ammonia and water

Answer 27

all these molecules are tetrahedral shape as all have 4 pairs of electrons in the outer shell of the central atom

• however nitrogen in ammonia has one lone pair, oxygen in water has two lone pairs.
• this affects the bond angles because lone pairs carry a greater repulsive effect than bonding pairs.

Question 28

BONDING PAIRS

2) molecules containing double bonds

Answer 28

in VSEPR theory, a double bond is counted as a single bonding pair.

Question 29

INTERMOLECULAR FORCES

Answer 29

these forces are found between neighbouring molecules.

weak nature gives rise to low Melting and BP of covalent liquids and gases.

Question 30

INTERMOLECULAR FORCES

What are the three types of intermolecular forces?

Answer 30

1) london forces (induced dipole-dipole interactions)
2) permanent dipole-dipole forces
3) hydrogen bonds

Question 31

what are london forces?

Answer 31

• forces found between all atoms and molecules
• are the weakest of the intermolecular forces- arise bc electrons are always on the move.

for tiny fractions of a sec, there may be more electrons on one side of an atom, therefore the atom gains a TEMPORARY DIPOLE.

Question 32

LONDON FORCES

Whats happens when an atom has a temporary dipole?

Answer 32

it will attract the neighbouring atoms around it by inducing them with a dipole.
the more electrons present in an atom or molecule, the stronger the london forces.

Question 33

LONDON FORCES

boiling points of the noble gases?

Answer 33

increase down the group because the atoms have more electrons and stronger london forces and so more heat energy is needed to break them

Question 34

LONDON FORCES

boiling points of the alkanes?

Answer 34

increases as the length of the carbon chain increases because bigger molecules have more electrons and stronger london forces and more energy is needed to break them

Question 35

Permanent dipole-dipole forces

Answer 35

• these are found between molecules which have permanent dipoles.
• polar molecules arise from electronegativity differences in the atoms
• the + charge of one molecule is attracted to the - of another to form a dipole-dipole force.