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Proton One unit of positive charge
Electron One unit of negative charge
Valence electron The electron in the outer most energy level
Neutron No charge
Atom Smallest part of an element
Subatomic particles The 3 particles that make up an atom: proton, electron, neutron
Nucleus The place where protons and neutrons are located in an atom
Energy level Place where electrons are located. Also called shells or rings
Mass number Number of protons and neutrons in the nucleus. Atomic Mass is the term relating to the average number of protons and neutrons in nucleus (usually a decimal number)
Atomic number Number of protons in the nucleus
2-8-8 Relating to energy levels, 2 maximum electrons in 1st energy level; 8 maximum in the 2nd energy level; 8 maximum in the 3rd energy level
Isotope Atoms with the same number of protons but different number of neutrons
Ion Atoms that lose or gain electrons
Matter Anything that has mass and takes up space

ATOMS

Take a look around you. What do you see? A wall, a friend, a science book, money? All of these things are different in how they look, but the same in what they are made of. All of the above mentioned things are made of matter Matter is anything that has mass and takes up space. All matter is made of atoms. All atoms are made of 3 subatomic particles: protons, neutrons, and electrons. So really, all matter is made of protons, neutrons and electrons. No matter what object you hold in your hand, clothing you wear, or hair gel you use, they are all made out of the same subatomic particles.

If all matter is made of atoms, containing only those 3 subatomic particles, why doesn't all matter look basically the same? Simply because the atoms are different. Atoms have different numbers of subatomic particles, but the factor that distinguishes one atom from another is the number of protons an atom has in its nucleus. The number of protons is the atom's atomic number.

In order for atoms to be the same element, they must have the same number of protons. But atoms can be different in that they have different numbers of neutrons and electrons. An atom with different numbers of neutrons, but the same number of protons is called an isotope. An atom that loses or gains electrons is called an ion.

Atoms are put together in an orderly fashion. Most of an atoms mass is in its nucleus, the central most place in the atom. Protons and neutrons make up most of this mass, with each particle having a weight of 1 atomic mass unit (amu). The electrons are arranged around the nucleus in energy levels or rings. Each energy level can hold a certain amount of electrons. The first energy level can only hold 2 electrons. The 2nd energy level can hold up to 8, and the third energy level can hold up to 8 (for elements 11-18). An atoms outer most energy level can only hold up to 8 electrons. These outer most electrons are called valance electrons.

An easy was to remember proton number, neutron number, electron number and mass number is APE-MAN. No, not the hairy man that we all want to get a selfie with, but an acronym that helps us remember a little math trick.
Atomic# = Proton# = Electron#      Mass# = Atomic# + Neutron#

The atomic number is also called the proton number. The electron number (in a perfect atom) is always equal to the proton number. The mass number is the total number of protons and neutrons in an atom's nucleus