Question

An atom has the following electron configuration.

Answer 1

Answer: A. 2

Explanation: The outermost energy level shell is 4s2.

Answer 2

Answer:

This atom have 2 valence electrons.

Explanation:

The Electronic Configuration of the elements is the arrangement of all electrons of an element in energy levels and sub-levels (orbitals).

There are 7 energy levels, numbered from 1 to 7, and in which electrons are distributed, logically in order according to their energy level. Electrons with less energy will be spinning at level 1. Each level is divided into sub-levels. These sub-levels into which each level is divided can be up to 4. These 4 sub-levels are called: s, p, d, f. In the sub-level s there can only be a maximum of 2 electrons, in p there can be a maximum of 6 electrons, in the sub-level d 10 electrons and finally in the sub-level f there can be a maximum of 14 electrons.

In level 1 there is only one sub-level, which will be the s. In level 2 there are 2 sub-levels, the s and the p. At level 3 there are 3 sub-levels s, p and d. And at level 4 there are 4 sub-levels, the s, the p, the d and the f.

Then, you have the following electronic configuration:

$1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{3}$

Each number in front of each letter indicates the level to which the electrons belong, each letter (s, p, d) indicates the sub-level and each super-index indicates the number of electrons at that level and that sub-level.

Valencia electrons are the electrons found in the last electronic layer (called valence orbitals). These electrons are what determine the ability of the atom to form bonds. When an element joins another it does so through its valence electrons.   Remember that the last electronic layer belongs to the furthest level.

Looking at the previous electronic configuration, it can be seen that the last layer belongs to the last level, this being level 4. In this case this level has only one sub-level (sub-level s), which has 2 electrons.

So, it is possible to say that this atom have 2 valence electrons