Category :
8th Class
Materials: Metals and Non-metals
Synopsis
- Metals occur in combined state or in the form of compounds.
- Most of the metals are solids at room temperature except mercury which is a liquid.
- Most of the metals have high densities because their atoms form close clusters.
- Most of the metals shine and can be easily polished.
- Metals are malleable, so they can be hammered into thin sheets. They are also ductile and hence, can be drawn into thin wires.
- Metals are sonorous because they produce sound when struck.
- Most of the metals are good conductors of heat and electricity.
- Metals combine with oxygen to produce basic oxides. \[4Na+{{O}_{2}}\to 2N{{a}_{2}}O\]
- Metals react with water to form oxides and hydroxides.
\[Mg+{{H}_{2}}O\to MgO+{{H}_{2}}\]and\[2Na+2{{H}_{2}}O\to 2NaOH+{{H}_{2}}\]
- Metals react with dilute hydrochloric and sulphuric acids to produce respective salts and hydrogen.
\[2Na+2HCl+{{H}_{2}}\]and\[2Na+{{H}_{2}}S{{O}_{4}}\to N{{a}_{2}}S{{O}_{4}}+{{H}_{2}}\]
- Metals displace one another from their salts.
\[Mg+2HCl\to MgC{{l}_{2}}+{{H}_{2}}\]
- Metals react with chlorine to form chlorides.
\[Ca+C{{l}_{2}}\to CaC{{l}_{2}}\]
- Non-metals occur in Free State as well as in combined state.
- Many non-metals are solids or gases at room temperature.
- Non-metals look dull. Many of them are coloured.
- Non-metals are neither malleable nor ductile.
- Non-metals do not produce sound when struck.
- Non-metals are bad conductors of heat and electricity except graphite.
- Non-metals combine with oxygen to produce acidic or neutral oxides.
\[2{{N}_{2}}+{{O}_{2}}\to 2{{N}_{2}}O\]and \[S+{{O}_{2}}\to S{{O}_{2}}\]
- Non-metals cannot displace hydrogen from dilute acids and water. Thus, they do not react with them.
- Non-metals react with hydrogen to form covalent compounds. \[{{H}_{2}}+S\to {{H}_{2}}S\]
- Non-metals react with chlorine to form covalent chlorides. \[{{P}_{4}}+6C{{l}_{2}}\to 4PC{{l}_{3}}\]
- Corrosion of metals and its prevention
The slow destruction of some metals by chemical reactions is called corrosion. It can be prevented by
(i) applying paint or grease to avoid the contact with air on corrosive metals.
(ii)coating corrosive metal with non-corrosive metal.
(iii) mixing corrosive metals with non-corrosive metals by alloying.
