Why the size of atoms does not decreases regulary in a period
Answers
In the Periodic Table, there are a number of physical properties that are not really "similar" as it was previously defined, but are more trend-like. This means is that as you move down a group or across a period, you will see a trend-like variation in the properties. There are three specific periodic trends that we will discuss. The first lesson of this chapter is devoted to the trend in atomic size in the Periodic Table. The two following this lesson will discuss ionization energy and electron affinity. Each of these trends can be understood in terms of the electron configuration of the atoms.
The actual trends that are observed with atomic size have to do with three factors. These factors are:
1: The number of protons in the nucleus (called the nuclear charge).
2: The number of energy levels holding electrons (and the number of electrons in the outer energy level).
3: The number of electrons held between the nucleus and its outermost electrons (called the shielding effect).