Physical Properties of Metals and Metallic Bonding
We use metals in all our daily activities, from the metal in cars and aeroplanes to the knives and forks that we eat our meals with. Metals are shiny when cut, dense, strong, malleable and ductile. Metals are good conductors of heat and electricity.
At room temperature all metals except mercury are solid. Mercury is a liquid at room temperature. The physical properties can be related to the structure of metal.
Structure of Metals
Metal atoms that are positively charged are strongly attracted to the negative electrons.The outer electrons are free to move through the metal lattice.
The following table illustrates the physical properties and relates this to the structure of the metal.
|Physical Property||Quality or Appearance||Structural Explanation|
|Dense||Most are heavy.||Densely packed large atoms.|
|Ductile||Appears as a thin wire.||Atoms can slide over one another when drawn out to a wire.|
|Very Strong||Hard to bend and can hold large weights.||Strong attraction between the positive|
|Usually very high.||Strong attraction between the positive atoms and electrons.|
|Lustre||Shiny when cut.||Metal lattice reflects nearly all the light from an external source.|
|Electrical Conductivity||Conducts electricity well.||Outer electrons are free to move Conductivity through the metal lattice.|
|Heat Conductivity||Conducts heat well.||Densely packed atoms can vibrate and bump into one another easily, thereby heating up.|
|Malleable||Appears as a thin sheet.||Atoms can move past one another when beaten.|
Reactivity and Reactions of Metals with Oxygen, Water and Acid Reactivity
Metals vary in their reactivity. Some metals exist as the element in the ground whereas others exist as
a metal ore.
The order of reactivity is:
Na > Li > Ca > Mg > Al > Zn > Fe > Pb > Cu > Au
This means that Na is the most reactive and Au is the least reactive.
This reactivity depends on how easily a metal loses its electrons. Aluminium is very reactive; however, it forms a tough oxide layer which protects the metal.
When a metal reacts with oxygen, it forms a metal oxide. Rusting is the process where iron forms iron oxide.
The metal loses electrons to form the metal ion which is positively charged. The oxygen gains
electrons to be negatively charged.
Metal + Oxygen —> Metal Oxide
e.g. Iron + Oxygen —> Iron Oxide
Combustion is fast oxidation. Tarnishing is slow oxidation.
Some metals react with water. Like oxidation a metal ion is formed. When a metal reacts with water, a metal hydroxide and hydrogen forms.
Metal + Water —> Metal Hydroxide Hydrogen Gas
e.g. Sodium + Water —> Sodium Hydroxide + Hydrogen Gas
Metals vary in their reactivity with acids. Common acids are: hydrochloric, sulphuric, nitric, acetic (vinegar).
The aids are all sources of H+ ions which remove the electrons from the metals. The metal then forms a positive ion.
e.g. Magnesium + Hydrochloric Acid —> Magnesium Chloride + Hydrogen Gas
The metal has combined with the acid to form a salt.
Reactions of Metal Oxides, Hydroxides, Carbonates
and Hydrogen Carbonates
Metals easily form metal ions by losing electrons. They can then combine with other compounds
• Oxide, O2-
• Hydroxide, OH–
-• Carbonate, CO32-
Hydrogen carbonate. \HCO3–
The metal compounds can then react with water and acids to form other compounds.
A metal oxide is any metal that is combined with oxygen. Most metals form oxides easily — they can be formed by heating the metal in air. Most metal oxides are insoluble. However, the metal oxides that do dissolve in water form a metal hydroxide.
e.g. Sodium Oxide Water —> Sodium Hydroxide
Metal hydroxides are solids. Some dissolve in water, when they do they form:
e.g. Metal Oxide Water — Metal Hydroxide
Soluble metal hydroxides are alkaline, i.e. their pH is greater than 7. When a metal hydroxide reacts with an with water and salts are formed.
e.g. Metal Oxide + Acid – Water —> Salt
Sodium Hydroxide + Hydrochloric Acid —> Sodium Chloride + Water
This means a metal hydroxide can neutralise an acid, i.e. return it to a neutral pH.
Metal Carbonates and Hydrogen Carbonates
Metal carbonates and metal bicarbonates (hydrogen carbonates) are common compounds.
e.g. Calcium carbonate (CaCO3) is limestone; Sodium bicarbonate (NaHCO3) is baking soda.
They undergo two types of common reactions:
- With an acid
Metal Carbonate + Acid —>Salt + Carbon Dioxide + Water
e.g. Magnesium Carbonate Sulfuric Acid Magnesium Sulfate+Carbon Dioxide Water
- Decomposition with heat:
Metal Carbonate + Heat —> Carbon Dioxide + Metal Oxide
e.g. Copper Carbonate + Heat —> Copper Oxide + Carbon Dioxide
(green powder) (black powder) (gas)