How can you use the periodic table to determine the number of valence electrons an element has?
Elements are located on the periodic table based off of their atomic number, but the vertical columns they are in (groups) show how many valence electrons they have. If an element were in Group 3 of the periodic table, it would have 3 valence electrons, and so on. This doesn't apply to the Transition Metals, so one should skip straight to Group 14, where the elements all have 4 valence electrons. Group 15 has 5, Group 16, 6, etc. The one exception to this is Helium, which is in Group 18 but only has 2.
Rarely. The number of valence electrons of an element depends on it's position on the periodic table. Any given element can have between 1-8 valence electrons. The number of valence electrons increases left to right on the periodic table, while the number of protons, which determine the atomic mass and identity of an element, increase in general. Therefore the number of valence electrons can only equal the number of protons at the 8th element and…
You can determine how many valence electrons an atom has by what family the element of the atom is in. For instance, if the element is in family 8A, the number of valence electrons will be 8. Or, if the element is in family 2A, the number of valence electrons for the atom will be 2. So, whatever number family the atom is in, the number of valence electrons equals that.