Atoms of the same element with different mass number.  These have the same number of protons but a different number of neutrons.

Atomic Mass Units

1/12 of mass of carbon-12 atom mass

(mass)(%) + (mass)(%)

100

Thomson

A sphere of positive charge with electrons able to be removed from it.

[image]

Most of atom's mass was concentrated in the nucleus which lay in the center of atom.  Electrons revolved around the nucleus.

[image]

Bohr

Electrons orbit the nucleus like planets around the sun.

In the center of the atom.  Contains the protons and neutrons.

Atom is a solid sphere and is indivisible (cannot be broken down into smaller pieces).  Atoms of the same element are identical.

Positive ion.  Formed when an atom loses electrons.  Typically metals

Negative ion.  Formed when an atom gains electrons.  Typically a nonmetal.

Came up with math equations that describe where an electron might be (the probability) at a certain period of time.