2.2.2 bonding and structure

Question 1

Ionic bonding

Answer 1

Electrostatic attraction between oppositely charged ions formed by electron transfer

Giant ionic lattice

Ionic bonding between ions

Question 2

Properties of ionic compounds

Answer 2

High melting points - strong electrostatic forces between oppositely charged ions in lattice
- higher when ions are smaller and/or have higher charges

Non conductor of electricity when solid - ions held together tightly in lattice and can’t move so no charge conducted

Good conductor of electricity when in solution or molten - ions are free to move when in solution and molten so can carry a charge

Usually soluble in aqueous solvents

Question 3

Covalent bonding

Answer 3

Strong electrostatic attraction between a shared pair of electrons and nuclei of bonded atoms

Question 4

Dative covalent bonding

Answer 4

When the shared pair of electrons in covalent bond come from only one of the bonding atoms

Aka co-ordinate bonding

E.g. NH4+, H3O+, NH3BF3

Question 5

Average bond enthalpy

Answer 5

Measurement of covalent bond strength

The larger the value, the stronger the covalent bond

Question 6

Covalent bond structure

Answer 6

Simple molecular

Intermolecular forces (induced/ permanent dipole-dipole/ hydrogen bonds) between molecules

E.g. iodine, CO2, H2O

Question 7

Molecular (simple) boiling and melting points

Answer 7

Low as weak intermolecular forces between molecules (specify type)

Question 8

Molecular conductivity

Answer 8

Poor as no ions to conduct and electrons are in fixed positions so cannot move to carry a charge

Question 9

Linear

Answer 9

2 BP, 0 LP

180

Question 10

Trigonal planar

Answer 10

3BP, 0LP, 120

Question 11

Tetrahedral

Answer 11

4BP, 0LP

109.5

Question 12

Trigonal pyramidal

Answer 12

3BP, 1LP

107

Question 13

Bent

Answer 13

2BP, 2LP

104.5

Question 14

Octahedral

Answer 14

6BP, 0LP

90

Question 15

How to explain shape

Answer 15

State no. BP + LP

State electron pairs repel and try to get as far apart as possible

If no LPs, state electrons repel equally

If there are LPs, then state LPs repel more than BPs

State actual shape and bond angle

Question 16

Lone pairs

Answer 16

Repel more than bonding pairs

Reduce bond angles by 2.5 per lone pair

Question 17

Electronegativity

Answer 17

Relative tendency of an atom in a covalent bond in a molecule to attract electrons towards itself in a covalent bond

Question 18

Most electronegative atoms

Answer 18

F, O, N, Cl

Question 19

electronegativity across a period

Answer 19

Increase across a period as proton number increases

atom radius decreases as electrons are in the same shell

Question 20

Electronegativity down a group

Answer 20

Decreases down a group as distance between nucleus and outer electrons increases

Shielding of inner shell electrons increases

Question 21

Formation of permanent dipole

Answer 21

When the elements in the bond have different electronegativities

When there is an unequal distribution of electrons in the bond, a dipole forms.

Element with the larger electronegativity will have the negative dipole

Question 22

Symmetric molecules

Answer 22

Will not be polar even if all individual bonds are polar

No net dipole

Question 23

Induced dipole-dipole where

Answer 23

All molecular substances and noble gases, not in ionic

Question 24

How London forces occur

Answer 24

In any molecule the electrons are moving constantly and randomly

As this happens electron density fluctuates and parts of the molecule become more or less negative

Temporary dipoles from this cause dipoles to form in neighbouring molecules (induced dipoles)

Question 25

Factors affecting size of induced-dipole

Answer 25

The more electrons, the higher the chance the temporary dipole will form

This makes the induced dipole-dipole interactions stronger between molecules and so boiling point increases

Question 26

Group 7 boiling point

Answer 26

Increase down the group

Increasing number of electrons, increases the size of induced dipoles interactions

More energy needed to overcome

Question 27

Alkane homologous series boiling points

Answer 27

Increases down the group due to increasing electrons

Increase in size of induced dipole-dipole interactions between molecules

More energy needed to overcome

Question 28

Shape of molecule boiling point

Answer 28

Longer straight chain alkanes have a larger surface area of contact between molecules for induced dipole-dipole interactions

Higher boiling point

Question 29

Hydrogen bonding

Answer 29

Between hydrogen and N,O,F

Question 30

Ice

Answer 30

Lower density - Molecules are held further apart than in liquid water

Hydrogen bonding - high boiling point

Question 31

Iodine

Answer 31

Covalent bonds between I2 molecules

Crystals contain regular arrangement of I2 molecules held together by weak induced dipoles