The elements in Periodic table are arranged in increasing order of their atomic numbers. All elements in the periodic table are also arranged in their metallic and non-metallic nature. Infect initially when there are few elements known, elements were classified as metal and non-metals.
Today we know that metals have tendency to lose their valence electron and form metal cation. They have loosely held valence electrons which can be easily released at normal temperature. On the contrary, non-metals have 5, 6 or 7 electrons in their valence shell so they have tendency to accept electrons to complete their octet.
Metal ions are bonded with their valence electrons by an electrostatic force attraction that is called as metallic bond. Because of metallic bonds between metal ions and free electrons, metals show some unique properties like malleability, ductility, electrical conductivity etc. Electron sea model of metallic bonding purposed that metal atoms lose their valence electrons and these free electrons move freely in metallic lattice.
Malleability is one of the unique properties of metals which allow them to deform by hammering or pressing to form sheets. Such substances are malleable substances. Non-metals are brittle and hard in nature. They cannot deform by hammering or pressing as they are hard and amorphous in nature. So metals are best examples of malleable substances.
The attraction force between metal ions and free electrons is nothing but metallic bond. Due to presence of free electrons, metals show unique properties compare to non-metals.
The substances that can deform into sheets by hammering are called as malleable substances like gold, silver, aluminum can be hammered into thin foils. Some other examples of malleable substances are lead, copper, tin, platinum, zinc, iron and nickel.
Materials which can deform under compressive stress can show malleability. Malleability of gold and silver metals makes it useful in manufacturing of ornaments.
It is one of the unique qualities of metals. Some of the metals require more pressure to compress like iron whereas some of the metals can be deformed by hitting under less stress. Metals from group 1 to 12 in periodic table show malleability. Another property of metals is ductility which is a related plasticity and such materials can be stressed into wires.
Gold is most malleable metal. We know that metals have tendency to lose their valence electrons and change to metal ions with positive charge. These positively charge metal ions are bonded with free valence electrons through electrostatic force of attraction.
Metals have close packed structure in which each metal ion is surrounded with other metal ions. For example in 12 coordinated metallic structures, each metal atom is surrounded with other 12 metal atoms. Similarly in 8-co-ordination, each metal atom is surrounded by eight other metal atoms. Such type of structure is common in Group-1 metals.
In both of the crystal structures, free electrons are moving randomly and as we apply external stress on metallic crystal, one layer of metal atoms slides over next layer but bonding remain same due to free electrons in crystal.
Metals are malleable and can be beaten into sheets because metal atoms can roll over each other into new positions without breaking the metallic bond when we apply some stress on metallic crystal. When a small amount of stress is applied onto metal, the layers of atoms will start to roll over each other. But at the same time, when we remove stress, metals atoms will fall back to their original positions. So we can say that metals are elastic in nature.
When we apply large stress, metal atoms roll over each other but cannot back to their original position and changed permanently. Since the layers of metal atoms do not arrange properly, so rolling of layers is hindered by boundaries. Boundaries are such place between metal atoms where atoms are not in contact with other atoms.
So as the area of boundaries increases, metal becomes harder and brittle. Some of the metals are not malleable but soft and can cut with knives like sodium, potassium etc. They are soft because they have less number of valence electrons or less number of metallic bonds so metal atoms are not closely packed and can cut with knife.