Write the electronic configuration of the atom

What is the electronic configuration of an atom described in in the article, the algorithm will be described here.

Determine the number of electrons

The first thing we need is to determine the number of electrons in a given atom, the number of electrons is equal to the ordinal number of the element. For example, for chromium - 24, for hydrogen - 1, and for chlorine - 17.

If the atom has no specified charge, it is considered zero, if there is a positive or negative the charge of the atom is indicated accordingly:

Cr²⁺ - positive charge
Cl^- - negative charge

We add the specified number to the ordinal number if it is a minus and subtract it if it is a plus:

Cr²⁺ → 24 - 2 = 22
Cl^- → 17 + 1 = 18

This is the only correct way to determine the number of electrons in an atom.

Write down the order of energy sublevels

If you forget in what order the energy sublevels go, make this drawing:

Figure 1. The order of filling energy levels

The order of energy sublevels is as follows: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

Fill energy sublevels with electrons

The number of electrons at the energy sublevels: for s is 2 electrons, for p - 6, for d - 10, for f - 14. If you don't understand why - read the article carefully (link at the beginning of the page).

We take the number of electrons and fill them alternately, for 1s - 2, for 2s - 2, for 2p - 6 and so on, until the electrons they won't end.

How to fill the last energy level correctly

Each sublevel is filled first with one electron per orbital, then the remaining ones are distributed.

For example, an oxygen atom has eight electrons, the configuration looks like this: 1s²2s²2p⁴. At the 2p level, there are two electrons in one orbit, on the other two one at a time!

Exceptions

What is the rule without exception? The following have deviations in the normal filling of the electronic configuration elements: ₂₄Cr, ₂₉Cu, ₄₁Nb, ₄₂Mo, ₄₄Ru, ₄₅Rh, ₄₆Pd, ₄₇Ag, ₇₈Pt, ₇₉Au. You need to remember their configuration! (grayed out in electronic configuration table)