EL - Bonding and structure *01 *02

Question 1

what is ionic bonding?

Answer 1

when ions are stuck together by electrostatic attractions

ions are formed when electrons are transferred from one atom to another

overall charge zero

Question 2

what are electrostatic attractions?

Answer 2

the forces that hold positive and negative ions together

- very strong

Question 3

what is a giant ionic lattice

Answer 3

ionic crystals are giant lattices of ions

giant because made of the same unit over and over again

within the lattice, the ions with different charges attract each other and the ions with the same charge repel each other. the ions arrange themselves to maximise attractions and minimise repulsions

Question 4

examples of a giant ionic lattice?

Answer 4

Sodium chloride

Na+ Cl-

Question 5

Behaviour of ionic compounds

Answer 5

1. conduct electricity when molten or dissolves - the ions are free to move so charge can move
2. high melting points - giant ionuc lattices held together by strong electrostatic forces, it takes lots of energy to overcome these forces so melting point very high.
3. often soluble in water - water molecules are polar, the water molecules pull the ions away from the lattice and cause it to dissolve

Question 6

what is covalent bonding?

Answer 6

when atoms share electrons so they both have a full outer shell of electrons

both the +ve nuclei are attracted electrostatically to the shared electrons

Question 7

what are simple covalent molecules?

Answer 7

substances made up of small molecules

Question 8

properties of simple covalent molecules?

Answer 8

1. fairly low melting point (no giant structure that needs to be broken down)
   - don’t need to overcome covalent bonds that hold atoms together only the electrostatic forces between the molecules (these are weak)
2. don’t conduct electricity - no charge carriers
3. usually insoluble in water (very slightly) - polar water molecules more attracted to each other than the molecular substance

Question 9

what is dative covalent bonding?

Answer 9

when one atom donates both electrons to a bond

Question 10

covalent bonding: exceptions to full outer rule

Answer 10

BF3 (B 6 electrons in outer shell, F 8 electrons in outer shell)

SF6 (S 12 electrons in outer shell, F 8 electrons)

Question 11

what are giant covalent structures?

Answer 11

these structures have a huge network of covalently bonded atoms

the electrostatic forces holding the atoms together in these structures are much stronger than simple covalent molecules

Question 12

examples of giant covalent structures

Answer 12

carbon and sillicon

Question 13

giant covalent structures: carbon and silicon

Answer 13

each atom is bonded to its 4 neighbours in a tetrahedral arrangement

Question 14

giant covalent structures: silicon dioxide (SiO2)

Answer 14

each atom bonded to 4 neighbouring atoms with oxygen atoms between each silicon atom

Question 15

properties of giant covalent structures

Answer 15

1. very high melting points - need to break lots of very strong bonds before the substance melts which takes a lot of energy
2. extremely hard - very strong bonds all through lattice arrangement
3. good thermal conductors - vibrations travel easily through lattice arrangement
4. won’t dissolve - covalent bonds mean atoms are more attracted to their neighbours in the lattice than to solvent molecules (all insoluble in polar solvents shows they don’t contain ions)
5. cant conduct electricity - no charged ions or free (graphite can)

Question 16

what is metallic bonding?

Answer 16

the electrons in the outermost shell of the metal atoms are delocalised (free to move)

this leaves a +ve metal ion

the positive metal ion are attracted to the delocalised -ve electrons

they form a lattice of closely packed +ve ions in a sea of delocalised electrons - this is metallic bonding

so metals exists as GIANT METALLIC STRUCTURES

Question 17

properties of metals: melting point

Answer 17

1. melting points - generally high because of the strong metallic bonding. the number of delocalised electrons per atom affects the melting point.
   - the more electrons the stronger the bonding will be so the higher the melting point
   eg Mg2+ higher than Na+ as has two delocalised electrons per atom
   - size of the metal ion and the lattice structure also affects the melting point.

Question 18

properties of metals: ductile?

Answer 18

yes

metals can be shapes and are ductile as there are no bonds holding specific ions together, so metal ions can slide over each other when the structure is pulled

Question 19

properties of metals: thermal conductors?

Answer 19

good thermal conductors

delocalised electrons can pass kinetic energy to eachother

Question 20

properties of metals: electrical conductors?

Answer 20

good electrical conductors

delocalised electrons are free to move and can carry a charge

any impurities can dramatically reduce electrical conductivity by reducing the number of electrons that are free to move and carry charge –> the electrons transfer to the impurities and form anions.

Question 21

properties of metals: soluble?

Answer 21

insoluble

except in liquid metals because of the strength of the metallic bonds

Question 22

what does molecular shape depend on?

Answer 22

electron repulsion

electron pairs repel each other as much as possible

Question 23

Linear molecules

Answer 23

2 areas of electron density
both bonding pairs
bond angle 180

Question 24

Trigonal planar molecules

Answer 24

3 areas of electron density
all bonding pairs
bond angle 120

Question 25

Bent molecules

Answer 25

3 areas of electron density
2 bonding pairs
1 lone pair
bond angle 120

Question 26

Tetrahedral molecules

Answer 26

4 areas of electron density

all bonding pairs = 109.5

3 bonding pairs = 107

2 bonding pairs = 104.5

minus 2.5 for each lone pair

Question 27

trigonal bipyramidal molecules

Answer 27

5 areas of electron density
all bonding pairs

120 and 90

Question 28

octahedral

Answer 28

6 areas of electron density
all bonding pairs
bond angle = 90

Question 29

structure of compounds that have a sodium chloride type lattice

Answer 29

ionic bonding is the overall attraction in a lattice and is made up of attraction between ions of different charge and repulsion between ions of the same charge