When we go left to right in an atomic table we can see that the electron num in the last orbit of an attom increase .So attraction between nucleus and electron increases. So the orbit/orbits come/ comes closer to nucleus. So when we go left to right in an atomic table.. we can see the radius of an attom decreases

Atomic Radius on Going from Left to Right in a Period

Introduction:
The atomic radius is defined as the distance between the nucleus of an atom and its outermost electron. It is an important property of an atom as it determines the size of the atom. In a periodic table, the atomic radius generally decreases from left to right in a period.

Explanation:

1. Definition of Atomic Radius:
The atomic radius is a measure of the size of an atom. It is usually expressed in picometers (pm) or angstroms (Å). The atomic radius can be determined by measuring the distance between the nuclei of two adjacent atoms that are chemically bonded together.

2. Factors Affecting Atomic Radius:
The atomic radius is influenced by two main factors:
- The number of electron shells: As the number of electron shells increases, the atomic radius also increases.
- The effective nuclear charge: The attractive force between the positively charged nucleus and the negatively charged electrons affects the size of the atom. As the effective nuclear charge increases, the atomic radius decreases.

3. Trend of Atomic Radius in a Period:
In a period of the periodic table, the atomic radius generally decreases from left to right. This can be explained by the following factors:

a) Increasing Effective Nuclear Charge:
As we move from left to right in a period, the number of protons in the nucleus increases, resulting in a higher effective nuclear charge. The increased positive charge in the nucleus attracts the electrons more strongly, pulling them closer to the nucleus. This leads to a decrease in the atomic radius.

b) No Significant Increase in Electron Shells:
In a period, the number of electron shells remains relatively constant. The additional electrons added to the outer shell as we move from left to right do not significantly offset the increased positive charge in the nucleus. As a result, the attractive force between the nucleus and electrons becomes stronger, causing the atomic radius to decrease.

4. Exceptions:
There are a few exceptions to the general trend of decreasing atomic radius across a period. For example, the atomic radius of noble gases remains relatively constant within a period as they have completely filled electron shells and do not readily gain or lose electrons.

Conclusion:
In conclusion, the atomic radius generally decreases from left to right in a period of the periodic table. This is due to the increasing effective nuclear charge and the absence of a significant increase in the number of electron shells. However, there are exceptions to this trend, such as noble gases. Understanding the trend in atomic radius is important in predicting and explaining the chemical behavior of elements.