# Electrons in Atoms

## Electron Configuration

where electrons are located within an atom

-Energy level

-sublevel

-orbital

-spin of each electron

electron configuration is used by using the diagonal rule with the diagram (below), starting at the top and making your way down based on the number of electrons in the atom.

for example: Oxygen [O], has 8 electrons. So in order to show the electron configuration, you would start at 1s, and use it for 2 electrons. Then to 2s, and 2p. Each level holds a maximum number of electrons, and this is what makes you go down the line. So, 1s(2),2s(2),2p(4), because the numbers add up to 8.

## Orbital Notation

-lowest energy to higher energy

-full orbitals are the best situation

-adding electrons can change energy of the orbital

-half-filled orbitals have a lower energy and are next best which makes them more stable and changes the filling order

Orbital notation is based off of the electron configuration you have written (above). You write orbital notation using arrows, which is another way to show the amount of electrons in the atom. Each line holds 2 arrows, and you always fill the lines with "up" arrows first. Each level has a certain number of lines filled as well. S holds 1 line with 2 arrows because s holds 2 electrons. P holds 3 lines with 2 arrows each because p holds 6 electrons, and so forth. So as shown (below), [O] has 8 electrons which means not every line will be filled in the p sublevel. The first two lines are filled because they are s lines, and the last 3 lines have the "up" arrows first, so it is in order.

## Noble Gases and Ions

Ions are atoms gaining or losing electrons to be like noble gases, because noble gases are stable. So when an atom has a positive or negative number at the top, the atom is gaining or losing electrons.