Students should be able to:
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- --> O2-
Group 5 Non-metals gain three electrons
15P (2.8.5) P + 3e- --> P3-