Chemistry (for biologists)

atomic mass

Protons + neutrons of an element

Atomic number

Number of protons

Number of neutrons (how to calculate)

Mass number - atomic number

Lewis electron dot structure

Like the Bohr model, but only showing valence shell electrons

Bohr model of the atom

Simplified method of viewing an atom with showing electrons going around the nucleus

Ionic bonds

Formed when one atom gives up an electron to another atom and they come together due to the charge difference

Covalent bonds

Formed when atoms share electrons amongst themselves

When ionic vs covalent bonds form

Delta EN (change in electronegativity between atoms) <1.7 is covalent, else ionic

What elements always form covalent bonds amongst themselves

CHNOPS (Carbon Hydrogen Nitrogen Oxygen Phosphorus Sulfur)

Electronegativity

the “pulling power” of an atom to pull electrons to itself

ion

Charged atoms

isotope

Atoms of the same element with differing amounts of neutrons.

octet rule

Atoms with 2 or more shells are most stable when the valence shell has 8 electrons.

duet rule

The first five elements are most stable when the valence shell has 2 electrons.

“Crossing over” of elements example

2Li⁺¹+O^-2→Li₂O

Ionization example (sulfur)

S+2e^- → s^-2

Ionization example (lithium)

Li → Li^+1 + e^-

How to know the number of electrons

If the atom is not an ion, the atomic number is the number of electrons. If it is an ion, add or subtract electrons as indicated by the superscript

be familiar with the general organization of the periodic table ex.(where the metals  are, non-metals, highest and lowest electronegativities, etc. 

Metals on left, and the non metals on the right. The left has the lowest electronegativities (because they want to be rid of their electrons) while the right has higher electronegativities (except the noble gases) because they want to gain electrons. If it is near the top of the periodic table, it has a higher electronegativity, while if it is lower, it has a lower electronegativity.