# Can I get help understanding the periodic table?

in science we're doing stuff to do with the periodic table.. atoms, electrons, neutrons and also stuff like making some formulaes the same. It never seems to make sense to me.. And I have a test on it next week.. Anyone who knows what I'm going on about can you help me please?

Number of protons = atomic number. That's the big number on the periodic table. This determines which atom it is.

# Protons + # neutrons ~= atomic weight. Atomic weight is the little number on the table. So # neutrons ~= atomic weight - # protons. Round off the answer, you can't have half a neutron.

Number of electrons = number of protons, unless the atom is charged. If it has a +1 charge then it has 1 less electron (protons are positive, electrons are negatiive). If it has a -1 charge then it has 1 more electron.

Protons and neutrons are stuck strongly in the nucleus. Electrons orbit around the nucleus. So while electrons might come and go, the number of protons or neutrons should almost never change. Unless there's a nuclear reaction or radiation.