The atomic weight is the number of atoms in one mole of the element. The electron and proton have charges of equal magnitude and opposite sign. The atomic number is the number of protons in the nucleus. An atom is the smallest particle of an element that maintains the chemical identity of that element. The number above the element symbol on the periodic chart is the atomic number.
Some elements exist in pure form as polyatomic molecules.
All atoms of a given element have identical properties, which differ from those of other elements. Compounds form when masses of different elements combine in small whole-number ratios. The relative numbers and kinds of atoms are constant in a given compound. An alkene hydrocarbon with an empirical formula of CH 2 has a molecular weight of 98.2 amu. Balance the following chemical equation with the smallest whole number coefficient.