How is the periodic table useful?
The information on the periodic table can be used to figure out other things about the elements that aren't already given to you. Here are just a couple of examples, can you find more?
Periods and Groups
We now know that the period tells us how many electron shells an element has and the group tells us how many electrons are in that outer shell. Now we can use this information to do something else: make compounds.
We know from science class that elements can be put together to make compounds. This can only happen if one element is "missing" the same number of electrons on its outer shell as the other element has. They do not have to be in the same period.
For example, from the periodic table we can see that lithium is in group 1, which means it has 1 electron in its outer shell. Look to the right of the table - fluorine is in group 7. You can see that 8 electrons can fit on its outer shell, so it is missing 1. Since lithium has one electron on its outer shell, they can go together to "complete" the outer electron shell and become a compound, lithium fluoride. Try it with another 2 elements!
Atomic Mass and Atomic Number
On the last page, we learned that the atomic number is the same as the number of protons (which is also the same as the number of electrons) the element has. We also learned that the atomic mass is equal to the number of protons and neutrons put together.
Only knowing these 2 numbers, we can figure out how many protons, electrons, and neutrons any atom has.
- Protons = atomic number
- Electrons = protons = atomic number
- neutrons = atomic mass - protons = atomic mass - atomic number