ATOMS Basic building blocks of all matter. Matter – everything that has mass. The smallest particles into which an element can be divided and still be the same substance.

Atomic Structure Protons – positively charged particles inside the nucleus. Neutrons – neutral particles inside the nucleus that have No charge. Electrons – negatively charged particles in atoms found around the nucleus.

Atomic Mass Unit (amu) Unit of measurement for the mass of subatomic particles. 1 amu = 1.7 X 10 -24 They are TINY!!! .000000000000000000000017 grams Proton = 1 amu Neutrons = 1 amu Electrons = almost zero (TINIEST particle with the least mass) Most mass is in the nucleus with protons and neutrons Otherwise atoms are mostly EMPTY SPACE

Atomic Number The number of protons inside the nucleus of the atom. Determines the element. All atoms of an element have the same atomic number. Atoms have no charge because the # of protons (+ charge) is = to the # of electrons (- charge).

Isotopes Atoms of elements that have the same number of protons (atomic number) but a different number of neutrons inside the nucleus.

Mass Number The total number of protons and neutrons in an atoms nucleus. Protons + Neutrons = Mass Number

Atomic Mass The weighted average of the masses of all the naturally occurring isotopes of an element. Average of Protons + Neutrons of all an elements Isotopes = Atomic Mass

ELEMENTS Are atoms Identified by it’s atomic # (# of protons) Arrangement of electrons determines the elements properties such as conductivity and reactivity.

Energy Levels - Electron Clouds Regions around the nucleus where electrons are arranged. Electrons further away from the nucleus have more and more energy. Each level or cloud can hold a specific # of electrons. 1st level - 2 electrons 2nd level - up to 8 electrons

Valence Electrons The electrons in the outermost energy level (electron cloud). Very important because they determine how an element will react with other substances