Bonding and structure

Question 1

Ionic bonding

Answer 1

The electrostatic attraction between oppositely charged ions

Question 2

Ionic lattice

Answer 2

The oppositely charged ions attract each other and form a giant lattice in which each ion is surrounded by 6 oppositely charged ions. This gives ionic compounds great stability as the forces of attraction between the ions is very strong.

Question 3

Why do ionic lattices have a high melting point?

Answer 3

A lot of energy is needed to overcome the strong electrostatic forces of attraction between the oppositely charged ions. Melting pint increases with increasing ionic charge.

Question 4

Ionic compounds and solubility

Answer 4

The water molecules are attracted to the ions and surround the ions breaking it up.

Question 5

Ionic compounds and electrical conductivity

Answer 5

They do not conduct electricity when solid as the ions are in a fixed position and there are o mobile charge carriers. When it is liquid the ionic lattice breaks down and the ions are free to move and carry the charge.

Question 6

Covalent bonding

Answer 6

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 7

Dative covalent bond

Answer 7

This is when a shared pair of electrons has been supplied by only one atom. For example in Ammonia the hydrogen has no electrons

Question 8

Average bond enthalpy

Answer 8

A measurement of covalent bond strength, the larger the value the greater the strength.

Question 9

Linear

Answer 9

2 bonded pairs, 180 degrees

Question 10

Trigonal planar

Answer 10

3 bonded pairs, 120 degrees

Question 11

Bent

Answer 11

2 bonded pairs, 1 lone pair, 119 degrees

Question 12

Tetrahedral

Answer 12

4 bonded pairs, 109.5 degrees

Question 13

Trigonal pyramidal

Answer 13

3 bonded pairs, 1 lone pair, 107 degrees

Question 14

2 bonded pairs and 2 lone pairs

Answer 14

bent, 104.5 degrees

Question 15

6 bonded pairs

Answer 15

Octahedral, 90 degrees

Question 16

Why are molecules shaped the way they are

Answer 16

The electron pairs repel each other so that they are as far apart as possible. The arrangement of electron pairs minimalize repulsion and holds the atom in a definite shape. Also state the number of bonded pairs and lone pairs of electrons

Question 17

Electronegativity

Answer 17

The ability of an atom to attract the bonding electrons in a covalent bond, the higher the value on the pauling scale the more electronegative it is. It increases towards F on the periodic table, so top and to the right.

Question 18

Polar bonds and permanent dipole

Answer 18

The molecule contains covalently bonded atoms with different electronegativity. The bonded electrons are not shared equally. A polar molecule contains polar bonds with dipoles that do not cancel due to their direction.

Question 19

Types of intermolecular forces

Answer 19

London forces (induced dipole), permanent dipole and hydrogen bonding

Question 20

London forces

Answer 20

Weak intermolecular forces that exist between all molecules, they act between induced dipoles

Question 21

An induced dipole

Answer 21

Is caused by the movement of electrons which produces a changing dipole. At any moment an instantaneous dipole will exist due to the imbalance of electrons, this induces a dipole in a neighbouring molecule. These attract on another and there is a weak force of attraction between the 2 molecules. Induced dipoles are only temporary.

Question 22

What affects London forces

Answer 22

Molecules with more electrons have more ways of arranging their outer shell electrons, in any one moment an imbalance in the arrangement of electrons can occur and an instantaneous dipole is established. The more electrons there are the more chance of an instantaneous dipole. When there is a greater surface area, for example straight chain alkanes, there is a greater surface area on which the IMF can form, so they will have a higher boiling point.

Question 23

How London forces affect structure

Answer 23

In a solid state, simple molecular substances form a regular structure and are arranged in a regular lattice. The molecules are held in place by weak intermolecular forces and the atoms within each molecule are bonded together strongly by covalent bonds. The dipole is always in the same direction and they face the same way

Question 24

Lone pair repulsion

Answer 24

Each lone pair reduces the bond angle by 2.5 degrees

Question 25

Permanent dipole-dipole

Answer 25

Occurs between polar molecules, it is stronger then induced dipole interactions. It occurs in addition with induced dipole interactions.

Question 26

Hydrogen bonding

Answer 26

Occurs in compounds that have a hydrogen atom attached to either oxygen, nitrogen or fluorine, which must have an available lone pair of electrons. It occurs in addition to permanent and induced dipole-dipole interactions. It is the strongest type of intermolecular force.

Question 27

Why does H2O have such a high boiling point

Answer 27

Due to the hydrogen bonding

Question 28

Why is ice less dense then water

Answer 28

the hydrogen bonding holds water apart in an open lattice structure. The H2O molecules in ice are further apart then in water so it is less dense.

Question 29

Solubility of covalent substances in non polar solvents

Answer 29

When a simple molecular compound is added to a non-polar solvent, intermolecular forces form between the molecules and the solvent. These interactions weaken the intermolecular forces in the simple molecular lattice and the compound breaks down. So non polar substances are soluble in non-polar solvents.

Question 30

Solubility of non polar substances in polar solvents

Answer 30

Non polar substances tend to be insoluble in polar solvents. This is because the intermolecular forces between the polar solvent is too strong to be broken up.

Question 31

Polar substances solubility

Answer 31

They are soluble in polar solvents because they attract each other.

Question 32

Covalent compounds conductivity

Answer 32

There are no mobile charged particles in a simple molecular substances. This means that there is nothing to move and carry the charge

Question 33

Giant covalent

Answer 33

Many billions of atoms are held together by a network of covalent bonds to form a lattice. Silica, silicon, diamond, graphite, graphene, Buckminster fulerine and carbon nanotubes.

Question 34

Giant covalent melting point

Answer 34

Giant covalent lattices have a high melting point because covalent bonds are strong. High temperatures are needed to provide the large quantity of energy needed to break the many strong covalent bonds. As there is a strong electrostatic force of attraction between the shared pair of electrons and the nucleus.

Question 35

Giant covalent solubility

Answer 35

Insoluble as the covalent bonds holding the atoms in the lattice are too strong to be broken by the interactions with the solvent.

Question 36

Giant covalent conductivity

Answer 36

In diamond and silicon all outer shell electrons are involved in covalent bonding so none are available for conducting electricity. Graphene and Graphite can as they have free electrons which can move and carry the charge.

Question 37

Metallic bonding

Answer 37

The strong electrostatic forces of attraction between the positive lattice and the sea of delocalised electrons

Question 38

Metal conductivity

Answer 38

Metals are able to conduct electricity as the electrons are free to move and carry the charge.

Question 39

metal boiling point

Answer 39

High temperatures are needed to overcome the strong electrostatic forces of attraction between the positive lattice and the sea of delocalised electrons.

Question 40

Boiling point of simple molecular substances

Answer 40

Low due to the weak intermolecular forces which are easily broken. It is higher if they have hydrogen bonding or are polar as this is a stronger type of intermolecular force the London forces. The boiling point is also higher when there are more electrons as it means the London forces are stronger. When talking about boiling point nether refer to covalent bonding

Question 41

What metals have a higher melting point

Answer 41

Those with a higher charge as they have more delocalised electrons so there is a bigger electrostatic attraction between the positive lattice and the sea of delocalised electrons

Question 42

Melting point of metals as you go down the group

Answer 42

Going down the group, the size of the cation increases and the charge remains constant. The charge density thus decreases and the attraction between the cations and the delocalized electrons also decreases. The melting points and hardness therefore decrease.