Atoms Lab

Proton (+)Lives in the nucleus. How many protons you have decides which element you are.

Neutron (0)Also in the nucleus. No charge. Adds mass. Changing neutrons makes an isotope.

Electron (−)Tiny and fast, outside the nucleus. Gaining or losing electrons makes an ion.

proton neutron electron outer (valence) electron

Controls

Protons 1 to 20

Neutrons 0 to 30

Electrons 0 to 30

Do each one with the controls. A check mark appears when you get it.

Drag the slider to add electrons to a neutral atom, one at a time.

Shell (1, 2, 3, ...): a floor of the building. Higher number means more energy and farther from the nucleus.
Subshell (s, p, ...): a type of room on that floor. Floor 1 has only s. Floor 2 has s and p.
Orbital: one box. Each box holds at most 2 electrons, and they must spin in opposite directions (up arrow and down arrow).
An s subshell has 1 box. A p subshell has 3 boxes.

Lowest energy first: 1s, then 2s, then 2p, then 3s, 3p, 4s.
Hund's rule: in a subshell with several boxes, put one up arrow in each box before pairing any. Watch this happen on nitrogen, oxygen and fluorine.

An orbital is not a track like a planet's orbit. It is the region where the electron is likely to be found.

The three p orbitals point along three perpendicular directions: x, y and z. The picture squashes z into the page.

Show shared pairs as:

Valence electrons are the electrons in the outer shell. They are the ones that make bonds.
A line between atoms is a shared pair of electrons (2 electrons). One line is a single bond, two lines a double bond, three lines a triple bond.
Dots next to one atom are a lone pair: two electrons that belong to that atom only.
Atoms are happy with a full outer shell: 8 electrons (the octet rule), or 2 for hydrogen. Count a shared pair for both atoms.

Switch to dots and every line turns into the pair of dots it stands for. Same electrons, two ways to draw them.

Lewis diagrams are flat bookkeeping. Real molecules are 3D.