Pure substance definition in chemistry?

 A pure substance is a sample of matter with both definite and constant composition with distinct chemical properties. To avoid confusion, in chemistry a pure substance is often referred to as a "chemical substance".

If a hydrogen atom is neutral, it must also have  one electron. an oxygen atom (o) has an atomic number of eight (8). this means a neutral oxygen atom has eight protons and eight electrons. the element actium (ac) has an atomic number of 89, so it has 89 protons and 89 electrons in a neutral atom