Matter refers to anything that takes up space and has mass. Elements cannot be broken down to substances with different chemical or physical properties. 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.