Explain what you understand by covalent radius van der Waals radius , ionic radius and atomic radius How do they vary in a period and in a group ?

Explanation

### Step-by-Step Solution:

1. **Definition of Covalent Radius**:
- The covalent radius is defined as half the distance between the nuclei of two identical atoms that are bonded together by a covalent bond. It represents the size of an atom when it forms a covalent bond with another atom.

2. **Definition of Atomic Radius**:
- The atomic radius is the distance from the nucleus of an atom to the outermost shell of electrons. It can be determined by measuring the distance between the nuclei of two non-bonded atoms of the same element and dividing it by two.

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