CBSE Class 8 Science Metal and Non metals Chapter Notes. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.
METALS & NON-METALS
There are 118 chemical elements known at present on the basis of their properties all these elements can be broadly divided into two main groups metals and non-metals.
A majority of the known elements are metals. All metals are solid except mercury, which is a liquid metal. There are 22 non metals, out of which 10 nonmetals are solids, one nonmetal (bromine) is a liquid and remaining 11 nonmetals are gases.
The elements which are hard, lustrous and polished, drawn into thin wires (ductile), hammered into sheets (malleable) and good conductor of heat and electricity are called metals. Such as gold, silver, copper, aluminium (Al is the most abundant metal) and zinc.
Exceptions :- Sodium and potassium are soft metals which can be cut with a knife.
The elements which are usually brittle and can not be used to make sheets or wires, can not be polished and bad conductor of heat and electricity (except graphite) are called non-metals. Such as sulphur, phosphorus, oxygen, nitrogen etc. Oxygen is the most abundant element on the earth.
Generally, metals and non-metals occurs in nature in free as well as in combined state. The metals which can not be affected by air and water are occur in native or free state and such metals are known as native metals. For example, gold and platinum. The reactive metals such as sodium, potassium, calcium, aluminium, copper etc. are found in nature in combined state in the form of compounds. The silver and copper metals occur in nature, in free as well as in the combined state. The non-metals, which are usually reactive are found in the form of compounds, and other which are less reactive, found in free state. For example, oxygen and nitrogen (Air). Thus most of the metals and non-metals are formed in nature in the form of compounds. These are
as follows :
OCCURRENCE OF METALS
POSITION OF METALS AND NON-METALS IN THE PERIODIC TABLE
The elements which are placed on the left hand side and in the centre of the periodic table are called metals. Such as sodium potassium, magnesium and calcium. Exception hydrogen, it shows the some characteristic properties of metals and some of non-metals. So, it is also called notorious element. The elements which are placed on the right hand side of the periodic table are called Non-metals. Such as oxygen, nitrogen, chlorine, fluorine etc.
In the periodic table metals and non-metals are separated from each other by a zig-zag line. The elements which are placed in the zig-zag line show some properties of metals and some properties of non-metals are called metalloids. Such as boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and Astatine (At).
The position of metals, non-metals and metalloids are shown in a simple form in fig. of periodic table –
The metals which are present at the extreme left are known as light metals while those present in the centre of the periodic table are called heavy metal or transition metals. In general, the metallic character of element decreases on going from left to right side in the periodic table.
For Example :
Sodium is more metallic than aluminium because sodium is on the left hand side of aluminium. However, on going down the group the metallic character increases.
For Example :
Carbon is non-metal while lead is metal due to their position, carbon placed at the top and lead placed at the bottom in the 14th group of the periodic table.
DO YOU KNOW
1. What are metals ?
2. What are non-metals ?
3. What are native metals ?
4. Which non-metal is most abundant element on the earth ?
5. Which metals & non-metals are found in free state in nature ?
6. Which element (metals & non metals) are found in combined state in nature ?
7. Why copper and silver metals occur in nature, in free as well as in the combined state while sodium
potassium , calcium etc. are found in combined state ?
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