Click on highlighted words to go to the vocabulary page for definitions. Every page has links to the other pages at the bottom of the page.
Most pages will not open a another browser or tab, only the vocabulary and help and hints page links will open another tab. You can open the page in a new tab by right clicking the link and selecting "open link in new tab."
An elements atomic number, number of protons, and number of electrons are all the same, so once you know one you know all three.
Subtract the atomic number from the mass number to get the number of neutrons in an atom of the element.
Ions are atoms with the same amount of protons and neutrons