Define atomic radius. how does it vary in a group and in a period?
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Answers
Answer:
The distance between the centre of the atom and the outermost shell of atom is called atomic radius.
Explanation:
1. Atomic radius is distance between centre of atom and valence shell.
2. Atomic radius is expressed in the unit picometre ( pm ). [ 1 pm = 10 ¯¹² m ].
3. The size of an atom depends upon the number of shells.
4. More the number of shells, larger is the atomic size.
Variation or atomic radius in a group:
1. The vertical columns in the modern periodic table are called as groups.
2. When we go from top to the bottom of a group, atomic radius goes on increasing.
3. This is because the lower elements in a group contain more shells than the upper elements.
4. As a result of this, the distance between the outermost shell and nucleus increases.
5. The nuclear force of attraction goes on decreasing.
6. Hence, the atomic radius increases in a group from top to bottom.
Variation in atomic radius in a period:
1. The horizontal rows in the modern periodic table are called as periods.
2. When we go from left to right in a period, atomic radius goes on decreasing.
3. Also, the atomic number of the elements increases one by one.
4. As a result of this, the positive charge on the nucleus increases by one unit.
5. The electron gets added to the same outermost shell.
6. Due to the increased nuclear power, the electrons are pulled towards the nucleus.
7. Hence, the atomic radius goes on decreasing while going from left to right in a period.