has unique chemical properties and is made of one kind of atom
The nucleus of an atom contains positively charged particles called
and particles with no charge called neutrons.
are negatively charged particles that orbit the nucleus.
Atoms are electrically neutral: they always have an equal number of protons
The number of protons
of an atom is its atomic number, and gives the element unique chemical properties.
The sum of the number of protons
make up its mass number.