# In the diagram, how are valence electrons illustrated? How many valence electrons does each element have?

Jul 4, 2017

Well, I would think that the electrons on the outside being DARKER are a good sign that they are important.

And in fact they are; the valence electrons are crucial to effective chemical bonding, and are usually the sole participants in chemical reactions (as opposed to core participation).

Thus, there are $\boldsymbol{4}$ valence electrons in silicon atom, and $\boldsymbol{5}$ in phosphorus atom.

For simplicity, you can find valence electrons for main-group elements (i.e. not transition metals and not $f$-block elements) via their group number if it is less than $10$, or their group number minus $10$ if the group number is greater than $10$.

So, in principle (at least for non-transition metals and non-$f$-block elements), one can easily look across the periodic table and predict that oxygen has $16 - 10 = 6$ valence electrons, or boron has $13 - 10 = 3$ valence electrons.