9.06.1 Ions

Syllabus

When a metal atom reacts with a non-metal atom electrons in the outer shell of the metal atom are transferred.
Metal atoms lose electrons to become positively charged ions.
Non-metal atoms gain electrons to become negatively charged ions.
The charge on the ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 relates to the group number of the element in the Periodic Table.
The ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 have the electronic structure of a noble gas (Group 0).
Students should be able to
1. work out the charge on the ions of metals and non-metals from the group number of the element, limited to the metals in Groups 1 & 2, and non-metals in Groups 6 & 7.

What does this mean?

Atoms and Ions

In the Atomic Structure topic you learned that all atoms are neutral.

So they must contain equal numbers of negative electrons and positive protons.

However, protons are found in the nucleus, whereas electrons are in shells around the outside.

So it would be very difficult to add or remove protons, but much easier to add some extra electrons or take some away.

But gaining or losing electrons would mean that the number of positives and negatives is no longer equal.

This is no longer an atom. Any charged particle is an ion.

Why do atoms gain or lose electrons?

Atoms need to fill their outside (valence) shell for electronic stability.

If the outside shell contains 6 or 7 electrons then it may be able to gain enough electrons to become full.

If the outside shell contains 1 or 2 electrons then it may be able to lose these electrons, leaving a full outside shell below.

Gaining electrons makes an atom become a negative ion (an Anion).

Losing electrons means an atom has more protons than electrons - it becomes a positive ion (a Cation)

Atoms gain or lose electrons until their outside shell is full - like a Noble Gas (Group 0 element).

Noble Gases never form ions - their shells are already full.

Oxidation and Reduction.

O.I.L.R.I.G. - stands for Oxidation Is Loss, Reduction Is Gain

Metals (at GCSE) are found in Group I, II or III.

Their outer shells contain 1, 2 or 3 electrons.

So they become 1+, 2+ or 3+ ions by losing electrons - this OXIDATION.

Non-Metals (at GCSE) are found in Group V, VI or VII.

Their outer shells contain 5, 6 or 7 electrons.

So they become 3-, 2- or 1- ions by gaining electrons - this REDUCTION.

Predicting the charge of ions from their position on the Periodic Table

It's possible to predict the charge of the ions formed by many elements of the Periodic Table, except the Transition Elements.

Elements in Group 0 don't form ions - their outer (valence) shell is already full.

Other non-metals form negative ions (anions).

Elements in Group VII all require 1 more electron to fill their shells.

Eg. ₉F has electronic structure = ( 2. 7); ₁₇Cl is (2.8.7)

So all elements in Group VII will become 1^- anions.

Elements in Group VI all require 2 more electrons to fill their shells.

Eg. ₈O has electronic structure = ( 2. 6); ₁₆S is (2.8.6)

So all elements in Group VI will become 2^- anions.

Elements in Group V all require 3 more electrons to fill their shells.

Eg. ₇N has electronic structure = ( 2. 5); ₁₅P is (2.8.5)

So all elements in Group V will become 3^- anions.

Since non-metals undergo Reduction by gaining electrons, it's no surprise that metals lose electrons (Oxidation) to become positive cations.