Question

What is the nuclear charge on the periodic table?

Answer 1

We know that atoms are composed of a nucleus which consist of positively charged ions known as protons and neutral species known as neutrons and the nucleus is surrounded by a cloud of negatively charged ions known as electrons. These electrons are arranged into different energy levels known as shells which form layers surrounding the nucleus. The electrons present in the outermost shell of an atom are known as valence electrons.

Complete answer:
In an atom, a measure of the effect of the number of positively charged ions i.e., protons in the nucleus and their tendency to attract the negatively charged ions i.e., electrons in orbits around the nucleus is known nuclear charge.
The nuclear charge for each electron present in different orbits is not the same because the negatively charged ions present at different energy levels repel each other and negate some of the positive charge from the nucleus. The presence of electrons in the inner shell of an atom provides a shield to the valence electron and the nuclear charge experienced by the valence electron is less than the value expected. This is known as effective nuclear charge.
Knowing the effective nuclear charge of an atom, we can determine the minimum amount of energy which is required to remove an electron from the outermost electrons which is known as ionization energy. In the modern periodic table, effective nuclear charge decreases on moving down the group whereas it increases across the period.

Note:
Remember that the shielding effect on an atom is defined as a reduction in the effective nuclear charge on the electron cloud because of the different attractive forces on the electron in an atom. Effective nuclear charge can be represented in terms of screening constant as ${Z_{eff}} = Z - \sigma$.