Question

Fluorine has an atomic number 9. It is in period 2 of the periodic table. The diagram shows the electron dot diagram of a fluorine atom.

F with 2 dots each above, right, below and 1 dot left.

How many valence electrons are in an atom of fluorine?

two
seven
nine
seventeen

Answer 1

Fluorine has an atomic number of 9, which means it has 9 electrons. The electron configuration of fluorine is \(1s^2 2s^2 2p^5\). The valence electrons are the electrons in the outermost shell, which for fluorine are the 2s and 2p electrons.

In this case, the outermost shell (second shell) contains 2 electrons in the 2s subshell and 5 electrons in the 2p subshell, for a total of:

\[ 2 + 5 = 7 \]

So, the number of valence electrons in an atom of fluorine is **seven**.