L7 Ionic bonding

Question 1

What is a chemical bond?

- Why do atoms form bonds?

Answer 1

= the attractive force that holds two or more atoms together in a molecule.
They form bonds to gain stability:
- e- distribute themselves in orbitals for the most stable/lowest energy configuration
- rearranging e- between atoms allow the combined molecule to achieve even lower energy

Question 2

What is the Octet Rule?

Answer 2

= elements aim to become isoelectronic as Nobel gases - they adjust their valence shells by gaining/losing/sharing e- so they have full outer shells.
* Transition metals use an 18 e- rule instead

Question 3

What is electronegativity?

- what does it depend on?

Answer 3

= the ability of an atom to attract e- in a chemical bond towards itself
Depends on:
- the no. of protons in the nucleus 
- the size of the atom
- the amount of screening by inner e-

Question 4

What elements are considered highly electronegative?

Answer 4

Any element with an electronegativity greater than 3 on the Paulings scale = top RHS of the periodic table.
* Fluorine is the most electronegative element - small atom, high nuclear charge

Question 5

What is an ionic bond?

Answer 5

Electrostatic attraction between two oppositely charged ions, after one or more e- are fully transferred. Takes place between metals and non-metals and the formation of the bond involves a decrease in energy.

Question 6

What is a cation?

Answer 6

Positive ion formed by a metal atom losing e-.

Question 7

What is an anion?

Answer 7

Negative ion formed by a non-metal atom gaining e-.

Question 8

Define isoelectronic?

Answer 8

An atom having the same electronic configuration (same no. of electrons/electronic structure) as another atom.

Question 9

What are the properties of an ionic bond?

Answer 9

= electrostatic attraction

• Strong
• Non-directional
• Broken in polar solvents e.g. water -> dissolve
• Broken by physical changes e.g. melting

Question 10

What does non-directional mean?

Answer 10

That the strength of the ionic bond (the interaction between ions) is dependant on distance but not on direction.

Question 11

What are the features of ionic compounds?

Answer 11

• Formed between metals and non-metals
• Dissolve easily in water and other polar solvents - the bond is broken and the separated ions are solvated
• Conduct electricity whilst molten and in solution
• Form crystalline solids with high melting points

Question 12

What is an ionic lattice?

Answer 12

= Repeating 3D pattern of anions and cations in the solid-state - the ions are attracted to all other ions with the opposite charge.

• Giant structure
• Hard crystals - shatter (the structure deforms when ions with the same charge are forced together and then repel)

Question 13

What is lattice energy?

Answer 13

= The enthalpy of the formation when forming one mole of the ionic compound (solid) from its gaseous ions.

Question 14

What factors favour ionic bonding?

Answer 14

• Easy cation formation - low ionisation of the metal
• Easy anion formation - high electronegativity, small size and low charge of the non-metal
• Large electronegativity difference between the atoms
• High lattice energy

Question 15

How big are the ions?

Answer 15

• Cations (+) are smaller than the neutral, parent atoms: the remaining e- are held closer to the positive nucleus
• Anions (-) are larger than parent ions: larger e- clouds

Question 16

What is polarisation?

Answer 16

= The distortion of the e- cloud of an atom, that results in non-spherical ions and covalent character in the bond.

• The larger the ion & the greater no. of e-, the higher its polarisability
• Anions tend to be more polarisable

Question 17

What is polarising power?

Answer 17

= An atoms ability to distort the e- cloud of another atom.

• The smaller an ion & the higher its charge, the more polarising power it has
• Cations tend to have more polarising power

Question 18

What is Fajan’s Rule?

Answer 18

= predicts covalent character in ionic bonds, that ionic compounds are likely to have some covalent character if:

• The cation is small and/or has a high charge = highly polarising
• The anion is large and/or has a high charge = highly polarisable

Question 19

What are the features of purely ionic compounds v. ionic compound with covalent character?

Answer 19

Purely ionic:
- Low positive charge
- Large cation
- Small anion
Covalent character:
- High positive charge
- Small cation
- Large anion

Question 20

If a melting point is lower than expected, what is happening?

Answer 20

Covalent character/directionality weakens the strength of the ionic lattice.

Question 21

What is a polyatomic ion?

Answer 21

= ions made up of more than one type of atom

• The bonding between the atoms in the ion is generally covalent
• The no. of e- means the group has an overall charge

Question 22

How do you name ionic compounds?

Answer 22

1st word = Cation - usually the same name as the parent atom
(oxidation state of the metal)
2nd word = Anion:
- polyatomic = name of the ion
- one element = name of the element with suffix -ide
e.g. Copper (II) chloride