The number of electrons in the outer electron layer of an atom with a nuclear charge of +9.

The charge of the nucleus of a chemical element is due to the presence of protons. If the charge of the nucleus is +9, then the number of protons is p = +9. The sign of a chemical element is equal to the charge of an atom, the number of protons. The 9th number is fluorine. He stands in the second period in the seventh group. Finding fluorine in the second period shows that it has two layers. The second is external. The group number indicates that there are 7 electrons on the outer layer of fluorine.

1 layer – 2 electrons

2nd layer – 7 electrons.

If formula 1S22S22P5.

On the second layer, S – 2 and P – 5. 2 + 5 = 7.

Answer: this element is fluorine, on the outer layer it has 7 electrons.

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