1.5 Ions and Ionic Bonding

Question 1

Ions

Answer 1

An atom or group of atoms with a positive or negative charge. For example:
Cations
A cation is a positively charged ion which is formed when an atom or group of atoms loses one or more electrons

Cations usually form from hydrogen or metals:
Group 1 atoms lose 1 electron to form ions with one positive charge, +
Group 2 atoms lose 2 electrons to form ions with two positive charges, 2+

Anions
An anion is a negatively charged ion which is formed when an atom or group of atoms gains one or more electrons

Anions usually form from non-metals
Group 7 atoms gain 1 electron to form ions with one negative charge, -
Group 6 atoms gain 2 electrons to form ions with two negative charges, 2-

Question 2

Numbers of protons, neutrons and electrons in ions when given the atomic number and mass number

Answer 2

If there is a Calcium ion, Ca2+ (mass number 40, atomic number 20), this means that:
Protons = 20
Neutrons = 40 - 20 = 20
Electrons = 20 - 2 = 18

There would be 18 electrons since 2 electrons are lost to get to 2+ charge

Question 3

Ionic bonding

Answer 3

Ionic bonds are formed when electrons are transferred from one atom to another, resulting in oppositely charged ions that are attracted to each other due to electrostatic forces.

Question 4

Formation of ions in ionic compounds and the names of ions

Answer 4

Positively charged ions formed form hydrogen or metal atoms take the name of the element

Negatively charged ions formed from single non-metal atoms take the name of the element, but end in -ide

Negatively charged ions in compounds containing three or more elements, one of which is oxygen, end in -ate

Question 5

Properties of an ionic compound

Answer 5

The ions in an ionic compound form a lattice structure which has a regular arrangement of ions. There are ionic bonds between oppositely charged ions.

Melting and boiling points
Ionic compounds usually have high melting and boiling points since there are many strong ionic bonds and large amounts of energy must be transferred to the lattice structure to break these bonds.

Solubility in water
Ionic compounds are often soluble in water. They dissolve to form aqueous solutions.

Question 6

Deducing the formulae of ionic compounds

Answer 6

Oxide - involves O2- ion (e.g. sodium oxide Na2O)
Hydroxide - involves OH- ion (e.g. sodium hydroxide NaOH)
Halide - involves a -1 halide ion (e.g. sodium chloride NaCl)
Nitrate - involves NO31- ion (e.g. sodium nitrate NaNO3)
Carbonate - involves CO₃²⁻ ion (e.g. sodium carbonate NaCO3)
Sulfate - involves SO4²⁻ ion (e.g. sodium sulfate NaSO4)

Question 7

Ionic Formulae Rules

Answer 7

Ions should have the same number of charge, because then it is much easier to balance.

For example:
Hydrogen (H+) forms with Chlorine (Cl-)
the ionic formula would be HCl because the charges cancel out.

However, if hydrogen (H+) forms with oxygen (O2-)
the ionic formula would be H2O because you need to multiply hydrogen by 2 so the charges can cancel out.