Metals and non–metals
What do we understand by the terms “metals and non-metals”? For that we will first learn about the elements. An element is scientifically defined as a substance that is made of atoms of only one kind. It is the simplest form of matter that cannot be split into simpler substances or built from simpler substances by any ordinary or chemical or physical method. There are total 118 elements with their atomic number from 1 to 118. Out of which 92 occur naturally while the rest are prepared artificially in the laboratories.The periodic table houses these elements. The periodic table is an arrangement of elements on the basis of certain chemical properties. It starts with Hydrogen as the first element and ends with Ununoctium as the last one. Elements are classified as metals, non-metals and metalloids.
Classification of elements into metals, non-metals and metalloids
The elements are thus classified into 3 categories viz. Metals, non-metals, metalloids. They are classified on the basis of their physical and chemical properties. The periodic table co-relates their placements and properties. Metals occupy the left side of the table and non-metals occupy the right side. A zigzag line of metalloids separates metals from non-metals. Out of the 118 elements of the periodic table, 84 are metals, 7 are metalloids and rests of them are non-metals. The number is inexact as the boundaries between metals, nonmetals, and metalloids fluctuate slightly due to a lack of universally accepted definitions of the categories involved.
Metals and non-metals have particularly distinguishing characteristics which separates them from one another. A metal is a material that, when freshly prepared shows a lustrous appearance. Non-metals, on the other hand, are materials lacking these properties. Metalloids are materials or elements with properties intermediate to both metals and non-metals. Almost 25% of the earth’s crust is made of metals whereas two non-metals namely, Hydrogen and Helium, make up to almost 99 percentage of the universe and Oxygen nearly makes half of the earth’s crust in either elemental or compound form. So, it is necessary that we study both metals and non-metals along with their properties.
Occurrence of metals:
The crust of the Earth provides metals and it is a good source to extract metals. Metals exist in two states depending on their electropositive nature:
- In free or native state: Noble metals such as gold, silver platinum etc. which have least electropositive character occur in nature in free state.
- In combined state: Most of the metals occur in nature as their compounds. These metallic compounds occur in earth’s crust along with number of rocky and other impurities known as minerals.
Physical properties of metals:
- State: Metals are generally solid at room temperature. The solid or liquid state of metal depends upon the capacity of the metal to readily lose their outer shell electron to form metallic bond. Though we have an exception i.e. mercury which is in liquid state at room temperature.
- Luster: Metals are shiny and lustrous. They have the quality of reflecting light from their surface and have smooth surfaces. E.g. Gold, Silver etc.
- Ductility: Metals are ductile. This property of metals allows them to be stretched into thin wires.
- Malleability: Metals are malleable i.e. they can be beaten into thin sheets. Gold is the most malleable of all.
- Hardness: All metals are hard except sodium and potassium, which are soft.
- Conduction: Metals are generally good conductors of heat and electricity. Silver and copper are the best conductors. Lead is the poorest conductor of heat.
- Density: Metals generally have high densities and are heavy. Lithium has the lowest density whereas Iridium and Osmium has the highest density.
- Melting and boiling points: Metals generally have high boiling and melting points.
Chemical properties of metals:
- Electropositive character: Metals tend to have low ionization energies, and typically lose electrons when they undergo chemical reactions. They form cations with 1,2,3 charges.
- Metal oxides are generally basic in nature.
- Metal oxides react with acid to give salt and water.
- Metals act as a good reducing agent.
- They are easily corrosive.
Occurrence of non-metals:
Non-metals are extracted from Brine: Cl, Br, I; liquid air: N, O, Ne, Ar, Kr, Xe ; minerals and ores.
Non-metals show more variability in their properties than do metals.
- Physical state: Most of the non-metals exist in gases or solid. Bromine is in liquid state.
- Malleability and Ductility: Non-metals are brittle and cannot be roll into wires or sheets.
- Conduction: They are poor conductors of heat and electricity.
- Luster: These have no metallic luster and do not reflect light.
- Non-metals react with metals to form ionic compounds and with other non-metals to form co-valent compound. They are electronegative i.e. they gain electrons when bonding with metals except for noble gases they have completely filled orbits.
- Non-metals react with oxygen to form oxides. These oxides are acidic in nature and react with base to form salt and water.
The table above shows the trends in metallic and non-metallic character.