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