9.05.2 Metals and Non-Metals

Syllabus

Elements that react to form positive ions are metals.
Elements that do not form positive ions are non-metals.
The majority of elements are metals.
Metals are found to the left and towards the bottom of the Periodic Table. Non-metals are found towards the right and top of the Periodic Table.

Students should be able to:

explain the differences between metals and non-metals on the basis of their characteristic physical and chemical properties.
explain how atomic structure of metals & non-metals relates to their position in the Periodic Table
explain how the reactions of elements are related to the arrangement of electrons in their atoms and hence to their atomic number.

We know what we think a metals should look like, but an element that is a metal should also behave like a metal and react like a metal.

So what would we look for in a new element to decide whether it was a metal or non-metal?

A good guideline is that the metals should be good conductors of Electricity and heat; non-metals should be insulators.

Metals are generally malleable; non-metals brittle.

Metals are ductile (can be drawn into wires) and sonorous (make a ringing noise when struck).

They should be grey, lustrous (shiny) and have high melting-points and boiling points.

These are the Physical Properties of metals, Non metals should have almost the opposite physical properties.

Non-metals should be dull and have low melting points (if still solid at room temperature ) though half of them are gases even at room temp.

But there are exceptions: Mercury is a metal that is liquid at room temp; Carbon (Graphite) is a grey, shiny non-metal that can conduct.

So physical properties of metals/non-metals aren't the only thing we should think about.

We must also consider chemical properties - how elements react.

For this reason, we look at the OXIDES of elements to help decide whether they are metals or non-metals.

Metal Oxides are bases - they dissolve in water to form Alkalis.

Non-metal Oxides are Acidic.

Atoms gain or lose electrons to achieve a full shell.

Metals lose electrons, usually one, two or three depending on where they are on the Periodic Table.

So Group 1 metals lose one electron

₁₁Na (2.8.1) Na --> Na⁺ + e^-

Group 2 metals lose two electrons

₂₀Ca (2.8.8.2) Ca --> Ca²⁺ + 2e^-

Group 3 metals lose three electrons

₁₃Al (2.8.3) Al --> Al³⁺ + 3e^-

Losing one electron is generally easier than losing two, so Group 1 elements will be more reactive (react faster) than Group 2 elements.

Non-Metals gain electrons, usually one, two or three depending on where they are on the Periodic Table.

So Group 7 non-metals gain one electron

₁₇Cl (2.8.7) Cl + e^- --> Cl^-

Group 6 Non-metals gain two electrons

₈O (2.6) O + 2e^- --> O^2-

Group 5 Non-metals gain three electrons

₁₅P (2.8.5) P + 3e^- --> P^3-

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