Scientists Protons, Neutrons, Electrons

Energy Levels

Certain amount of electrons fit on each energy level in the electron cloud (2, 8, 18, 32, 50...) It is the outermost energy level that effects the chemical properties of the atom. The electrons at this level are called the valence electrons.

J.J. Thomson

Discovered electrons-the negatively charged particles in atoms. Since he knew that atoms were neutral, he inferred that a positively charged subatomic particle must exist to mediate the electrons. He described as atom as "plum pudding," or a chocolate chip cookie.

John Dalton

Early 1800's. Matter is made up of small particles called atoms, which cannot be split into smaller particles. Atoms cannot be created or destroyed. While atoms of the same element have the same properties, atoms of different elements have different properties. Atoms of different elements combine to make new substances.

Neutron

No charge (0)

Ernest Rutherford

1911. Did the gold foil experiment (on the test), from which he found out that there is a positive core to the atom called the nucleus (has the protons making it positive). Nucleus has most of the mass, and the electron whirl around the nucleus. Additionally, atoms are mostly empty space.

Niels Bohr

1913. He knew that atoms lose and absorb energy. Stated that electrons move in paths around nucleus called energy levels. Electrons in energy levels have a certain amount of energy. The farther an electron is from the nucleus, the more energy it has. Moreover, adding energy to an electron pushes it farther away from the nucleus.

James Chadwick

1932. Discovers that the neutron is the other subatomic particle in the nucleus. Neutron has no charge but is roughly same size/mass as proton. Neutrons help buffer the positive charges (protons) in the nucleus, since like charges repel.

Isotopes

Atoms of the same element that have the same number of protons, but different numbers of protons.

Erwin Schrodinger

Electron Cloud Theory: Instead of knowing exactly where the electron is, there's a probability of finding an electron on a certain energy level.

Democritus

Greek philosopher from 2000 years ago. All matter is made of tiny invisible atoms called atomos, which means "indivisible." There is a different kind of atom for each different type of substance.

Neutral Atom

In a neutral atom the number of protons is the same as the number of electrons.

Electron

Negative Charge (1-)

Proton

Positive Charge (1+)

Atomic Number

The number of protons in the atom. This distinguishes what element you are, and is how the periodic table is arranged.

Mass Number

The sum of protons and neutron is an atom. This is done there are different isotopes of atoms within an element with different numbers of neutrons.