Different atoms contain specific numbers of protons, neutrons, and electrons. Isotopes have different weights. Oppositely charged protons and electrons are attracted to each other. Atom's proton number determines atom's number of electrons and its chemical properties. Arrangement of atom's electrons is determined by total number of electrons and electron shell they occupy.
Energy is the ability to do work.
Bohr model helps determine number of electrons in outer shell. How atoms react with one another is dependent upon number of electrons in outer shell. In atom with one shell, outer shell is filled when it contains two electrons. Orbital is a volume of space where rapidly moving electrons are predicted to be found. An orbital has a characteristic energy state and a characteristic shape.