Chapter 3: Atoms and The Periodic Table

Outer level holds up to..

8e- (called valence electrons)

What are atoms?

Atoms are the smallest part of an element that still has the element's properties.

John Dalton's Theory (Disproved)

Atoms are the smallest particles and cannot be subdivided. Atoms of the same element are exactly alike in mass.

Nucleus

Center of an atom. Positively charged. Makes up 99.9% of the atom's mass.

Protons

Charge (+). Mass is equals to atomic mass unit (amu). Identifies the element/atom.

Electrons

Charge is negative (-). Mass is equal to 0 amu. Found outside the nucleus, in the electrons.

JJ Thomson

Credited with discovering the negative charged particles called electrons.

Rutherford

Credited with discovering the nucleus. Also concluded that atoms are mostly empty space.

1800's John Dalton's Theory (Still Accepted)

Every element is made of tiny unique particles called atoms. Atoms of different elements can join and form molecules.

Today's Theory

It has been determined that it is impossible to pinpoint an electron's exact position due to its tremendous speed. Electrons do not move around in definite paths.

Neutrons

Net charge (0) -neutral. Mass is equal to 1 amu. Helps to hold the nucleus together.

Niels Bohr

Suggested that electrons move around atoms in set paths around the nucleus. He said each path is an energy level.

Atomic Number

Tells you number of protons. Identifies the atoms.

Mass Number

The mass of an atom. # of protons +

Atom's Charge

They are neutral. All atoms have the same number of protons and electrons. Charges cancel each other out.

Energy level (1st level holds...)

up to 2e-

Energy level (3rd level holds...)

up to 8 or 18e-

Energy level (4th level holds...)

up to 8, 18, or 32e-

Energy level (2nd level holds...)

up to 8e-