Subatomic Particles

• Atoms are very, very small and typically have an atomic radius of about 0.1nm
• Atoms contain 3 types of subatomic particles: proton, neutron and electron
• Almost all of the mass of an atom is in the nucleus
• The radius of the nucleus is less that 1/10000 of the atomic radius of the atom
• Atoms have no overall charge because they contain an equal number of protons and electrons
• An atom of a particular element have the same number of protons
• Atoms of different elements have different numbers of protons
• The number of protons in an atom is called its atomic number
• The sum of the protons and neutrons in an atom is called its mass number
• In the modern periodic table, elements are arranged in order of increasing atomic number
• number of neutrons = mass number - atomic number