structures

Question 1

coordination number of an ion

Answer 1

Gives number of its nearest neighbours

Question 2

Crystal coordination number

Answer 2

Number of anions around each cation in an ionic lattice

Question 3

ionic solids

Answer 3

Giant lattices of positive and negative ions
Sodium chloride and caesium chloride

Question 4

sodium chloride

Answer 4

Six sodium ions surround each chlorine ion and six chlorine ions around each sodium ion only
Giant structure as we can’t state how many ions there are

Question 5

caesium chloride

Answer 5

coordination number of 8:8
Cs+ is larger than Na+ ion and more cl- can fit around it

Question 6

properties of an ionic solid
melting temperature

Answer 6

high
giant lattices are held by strong electrostatic forces between the opposite charged ions
takes a large amount of energy to overcome these forces of attraction

Question 7

properties of ionic solids
Solubility

Answer 7

Often soluble in water, water molecules are polar- oxygen atoms have a partial negative charge and hydrogen atoms a partial positive charge
in solution the oxygen ends of the water molecule are attracted to the positive ions and the hydrogen ends to the negative ions

Question 8

properties of ionic structures
Hard but brittle.

Answer 8

When force is applied, layers of ions slide of each other causing ions of the same charge to be next to each other
Ions repel each other and the crystal shatters

Question 9

properties of ionic structures
Poor electrical conducttivity when solid

Answer 9

But good conductor when Molten or dissolved as electric current will flow if charge particles are free to move when a potential difference is applied
In solid- Ions are fixed in position by strong ionic bonds but in molten or dissolved ions are free to move and will move to the electrodes of opposite sign so will carry a current

Question 10

giant covalent structures

Answer 10

Consist of networks of covalently bonded atoms that stretch throughout the whole structure

Question 11

Allotropes

Answer 11

different forms of the same element in the same state

Question 12

Diamond

Answer 12

Each carbon atom is covalently bonded to four others
The atoms arrange themselves in a tetrahedral shape
Bonding forces are uniform throughout structure

Question 13

properties of diamond

Answer 13

Very high melting temperature. Energy needed to break the strong covalent bond is very high
Extremely hard due to strength of covalent bond and geometrical rigidity of the structure
Insoluble in water - no ions to attract polar water molecules
Poor conduct of electricity - no free electrons or ions present to carry charge

Question 14

Graphite

Answer 14

Consists of layers of hexagonal rings
Each carbon is joined to three others by strong covalent bonds
Fourth electron from each carbon is delocalised
Layers are held together by weak van der Waals forces

Question 15

delocalised

Answer 15

An electron that is not attached to a particular atom- it can move around between atoms

Question 16

Simple molecular solids

Answer 16

Have covalent bonds within molecules had held together by weak intermolecular forces

Question 17

properties of simple molecular solids

Answer 17

• low Mt and Bt: Although covalent bonds within molecules are strong the intermolecular forces holding molecules together are weak and do not need much energy to break
• soft: Weak intermolecular forces between molecules are easily broken
• normally insoluble in H2O: no ions to attract polar water molecules but compounds can form hydrogen bonds with water and be soluble
  -Poor conductor: No delocalized electrons or ions to move and carry charge

Question 18

Iodine

Answer 18

Atoms are covalently bonded in pairs to form diatomic molecules
These molecules are held together by weak van der Waals forces and are arranged in regular patterns

Question 19

ice

Answer 19

in ice molecules are arranged in rings of six held together by hydrogen bonds
In this ordered structure water molecules are further apart than they are in liquid state and structure creates large areas of open space inside the rings and as a result, at 0 degrees, Ice is less dense than liquid water

Question 20

metals

Answer 20

When metals are close to each other each atom loses control over its outer electrons
These electrons are no longer restricted to a particular metal atom but are delocalised leaving a positive cation

Question 21

arrangement of metals

Answer 21

Regular arrangement of metal cations (lattice) Surrounded by a sea of delocalised electrons

Question 22

properties of metals
- High melting temperatures

Answer 22

Large energy is needed to overcome strong forces of attraction between nuclei of metal cations and delocalised electrons
Melting temperature is affected by number of delocalized electron per cation and the size of the cation

Question 23

properties of metals
Hard

Answer 23

Metallic bond is very strong

Question 24

properties of metals
Insoluble

Answer 24

No ions to attract polar water molecules- each metal cation represents rest of the atom apart from outer electron
That electron has not been lost and still the in structure

Question 25

properties of metals
Good conductors

Answer 25

In both solid and molten
Delocalised electrons can carry a current because when a potential difference is applied across the ends of metal, electrons will be attracted to and move towards, to the positive terminal of the cell
Also good thermal conductors because denuclearize electrons can pass kinetic energy to each other

Question 26

properties of metal
Malleable (shaped)
Ductile (drawn into a wire)

Answer 26

When a forces applied to a metal the layers of cations can slide over each other
but delocalized electrons move with cations and prevent forces of repulsion forming between layers

Question 27

prop of graphite
melting temp

Answer 27

high
strong covalent bond in hexagon layers

Question 28

prop of graphite
soft Slippery feel

Answer 28

Weak forces between layers are easily broken so layers can slide over each other

Question 29

prop of graphite
Insoluble

Answer 29

No ions to attract polar water molecules

Question 30

prop of graphite
Good conductor of electricity

Answer 30

Delocalise electrons are free to move along the layers (not from 1 layer from next) so an electric current can flow and conduct parallel to layers

Question 31

prop of graphite
Low density

Answer 31

Relatively large amount of space between layers because length of covalent bonds in the layers is much shorter than length of van der Waals forces between layers
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