Water, H 2 O, is a compound composed of molecules. The formula shows that water is made up of hydrogen and oxygen. The symbol for the element chlorine is Cl. The number of protons in an atom is called the atomic number. The number of protons plus the number of neutrons is the mass number.
Scientists lists the elements in the periodic table in order of atomic number.
Aluminum oxide is a dull looking coating on the outside of aluminum metal. The number of protons in an atom is called the atomic number. The number of protons plus the number of neutrons is the mass number. When an acid is added to a base, a chemical reaction occurs. The reaction produces water and a salt.