Metals and non-metals have contrasting physical properties
Malleable
Able to be hammered or pressed into shape without breaking.
Ductile
Able to be drawn out into a thin wire.
- Metals are usually shiny, strong and dense, with high melting points.
- Metals are good conductors of electricity and heat.
- Copper is used for electrical wiring because it conducts well and is ductile.
- Aluminium can be rolled into thin foil because it is malleable.
- Non-metals are usually dull, brittle when solid and poor conductors, with low melting and boiling points.
- Graphite is an exception, because it is a non-metal that conducts electricity.
Mercury is a metal that is liquid at room temperature and diamond is a non-metal with a very high melting point, so these properties are general patterns with exceptions.
Metals lose electrons while non-metals gain or share them
Ion
An atom or group of atoms that carries an overall electric charge.
- When they react, metal atoms lose electrons to form positive ions, such as Na+\text{Na}^{+}Na+ and Mg2+\text{Mg}^{2+}Mg2+.
- Non-metal atoms gain electrons to form negative ions, such as Cl−\text{Cl}^{-}Cl− and O2−\text{O}^{2-}O2−, when they react with metals.
- Non-metal atoms can also share electrons with other non-metals to form molecules, such as H2O\text{H}_2\text{O}H2O.
- Metal oxides are basic, and those that dissolve in water form alkaline solutions.
- Non-metal oxides are often acidic, so sulfur dioxide and carbon dioxide form acidic solutions in water.
Do not say that metals gain electrons when they react, because metal atoms lose their outer electrons to become positive ions.
Electron arrangement gives an element's group and period
Electron arrangement
The way an atom's electrons are distributed between the shells around its nucleus, written as numbers such as 2.8.1.
Group
A vertical column of the Periodic Table.
- Elements are placed in order of atomic number, so each element has one more proton and one more electron than the one before.
- Electrons fill the shells in order, with up to 222 in the first shell and up to 888 in each of the next two.
- For Groups 1 to 7, the group number equals the number of electrons in the outer shell.
- The period number equals the number of occupied shells.
- Sodium, atomic number 111111, has the arrangement 2.8.12.8.12.8.1, so it is in Group 1 and Period 3.
- Find the group and period of chlorine, atomic number 171717.
- Fill the shells: 2.8.72.8.72.8.7.
- Seven outer electrons place chlorine in Group 7.
- Three occupied shells place chlorine in Period 3.
Few outer electrons place metals left and centre
- Atoms of metals usually have 1, 2 or 3 outer electrons, which they lose relatively easily.
- This places most metals on the left-hand side and in the centre of the table.
- Aluminium, with the arrangement 2.8.32.8.32.8.3, is a metal in Group 3.
- Atoms of non-metals usually have 4 to 7 outer electrons, or a full outer shell in Group 0.
- This places the non-metals on the right-hand side of the table.
- A staircase line running from boron down to astatine roughly divides the metals from the non-metals.
The atomic number sets the number of outer electrons, which decides both where an element sits and whether it behaves as a metal or a non-metal.
- Give three physical properties that distinguish metals from non-metals.
- What type of ion does a metal atom form, and why?
- What is the electron arrangement of magnesium, atomic number 121212?
- How do the group and period of an element relate to its electron arrangement?
- Why are most non-metals found on the right of the Periodic Table?
