Question

What is the number of core and valence electrons for I?

Answer 1

Hint: To find out the number of core and valence electrons for I, we need to first write down the electronic configuration of iodine. Electronic configuration depicts how the electrons in an ion, atom, or a molecule are distributed and arranged in its atomic shells, subshells and orbitals. The atomic number of Iodine is 53.

Complete answer: The atomic number Z of an element can be defined as the number of protons that are present in the nucleus of every atom of that element. Every element has a unique atomic number.
When an element is neutral and has no charge, the number of electrons present in an atom is equal to the atomic number.
Since the atomic number of iodine is 53, hence it has 53 electrons around its nucleus.
Valence electrons are the electrons that are present in the outermost shell of an atom.
Valence shell electrons have the highest energy level and can be determined by the shell which has the highest principal quantum number (n).
All the electrons in an atom except valence electrons are known as core electrons.
Total number of electrons = number of core electrons + number of valence electrons
Valence electrons of an element can be calculated using two simple steps.
1. First, electronic configuration of the element must be written. This will help us figure out how many electrons are there in the outermost shell.
$${}^{53}I:1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{6}5s^{2}4d^{10}5p^5$$
2. Determine the number of electrons in the outermost shell.
Here we can see that the outermost shell is the 5th shell for which the principal quantum number n=5.
The 5th shell in iodine has 7 electrons, 2 from s subshell and 5 from p subshell. Hence the number of valence electrons in iodine is 7.
So, the number of core electrons in iodine is 53-7=46.

Note: It should be noted that the electrons present in the outermost shell, or the valence electrons are the ones that participate in molecule or chemical bond formation. Where core electrons do not participate in molecule or chemical bond formation.