Positive Ions

Section 1 of 8From atom to ion

1Neutral atom

• Neutral atom Equal numbers of protons (positive) and electrons (negative), so no overall charge.

2Energy absorbed

• Energy absorbed An outer electron gains enough energy, for example from radiation, to escape the attraction of the nucleus.

3Electron lost

• Electron lost The atom now has more protons than electrons.

4Positive ion

• Positive ion The overall charge is positive: losing one electron gives a +1 ion, losing two gives +2.

Section 2 of 8Counting particles

Particle	Protons	Electrons	Charge
Sodium atom, Na	11	11	0
Sodium ion, Na+	11	10	+1
Magnesium ion, Mg2+	12	10	+2
Aluminium ion, Al3+	13	10	+3

Section 3 of 8Working out the charge

1

Count the protons from the atomic number; this never changes during ionisation.

2

Count the electrons the particle actually has, e.g. 10 for a sodium ion.

3

Subtract: charge = number of protons − number of electrons.

4

For sodium, 11 − 10 = +1, so the ion is written Na⁺. For magnesium with 12 protons and 10 electrons, the charge is +2, written Mg²⁺.

Section 4 of 8Ionisation and radiation

Ionising radiation

Alpha particles

• Alpha particles Strongly ionising because they have a large charge and mass, but they are stopped by paper.

Beta particles

• Beta particles Moderately ionising; they travel further, penetrating a few millimetres of aluminium.

Gamma rays

• Gamma rays Weakly ionising but very penetrating, requiring thick lead or concrete.

Section 5 of 8Metal atoms and positive ions in chemistry

Full outer shell

• Full outer shell A metal atom loses its outer electrons so that the remaining shell is full, which is a stable arrangement like a noble gas.

Group number

• Group number Group 1 metals form +1 ions, Group 2 metals form 2+ ions and Group 3 metals form 3+ ions, matching the number of outer electrons lost.

Ionic compounds

• Ionic compounds Positive ions are attracted to negative ions by strong electrostatic forces, forming a giant ionic lattice such as sodium chloride.

Section 6 of 8Negative ions for comparison

Gaining electrons

• Gaining electrons Non-metal atoms such as chlorine and oxygen tend to gain electrons,
  • giving more electrons than protons and an overall negative charge, e.g. Cl⁻ and O²⁻.

Why it matters

• Why it matters Positive and negative ions together make ionic compounds, and the total positive charge always equals the total negative charge.

Section 7 of 8Key terms

Term	Meaning
Ion	An atom or group of atoms with an overall electric charge.
Ionisation	The process in which an atom loses or gains electrons to become an ion.
Positive ion	An atom that has lost one or more electrons.
Ionising radiation	Radiation with enough energy to remove electrons from atoms.
Electron shell	An energy level in which electrons surround the nucleus.
Electrostatic force	The force of attraction between oppositely charged particles.

Section 8 of 8Exam technique

1

Saying an atom becomes positive by gaining protons; the number of protons never changes in ionisation.

2

Describing the loss of an electron as making the atom a different element.

3

Mixing up chargeslosing electrons gives a positive ion, gaining electrons gives a negative ion.

4

Stating that gamma is the most ionising radiation because it is the most penetrating; it is the least ionising of the three.