CHEM UNIT 1:

Atomic number: the number of protons and/or electrons
- when an atom loses electrons: positively charged ion (cation)
- when they gain electrons: negatively charged (anion)
*atomic mass: sum of protons + neutrons (mass # - atomic # = # neutrons) *
- atomic number increases as you move down a group
Isotopes: atoms that have different neutrons
- ex: carbon-12 or carbon-14
- when isotopes undergo change, the process is called radioisotopes average atomic mass: what is it?
- the average natural abundance of all isotopes of an atom.
- what is natural abundance? “measures how relatively common (or rare) the element is, or how much of the element is present in a given environment by comparison to all other elements” basically the average of all the isotopes

AVERAGE ATOMIC MASS = (pna1)(mass#1) + (pna2)(mass#2) + …
*all pna’s add to 100%* pna = percent natural abundance
- remember to change each pna to a decimal (100% - 1, 35% - 0.35)

Atomic radius:
- size is dependant on how many energy levels there are
- the more protons than neutrons than there is stronger bonding between nucleus and electrons - makes the atom smaller because the electrons are tightly held
- this is a positive charge because the electrons are negative and the nucleus (positive) is more dominant than the electrons
VS. an atom with more electrons than protons, making it a negatively charged atom. metals have a large atomic radius due to the fact that there are more electrons, making it easier for them to lose them aka react.
*remember metals react by losing electrons (cation) and nonmetals react by gaining (anion)* the more reactive a metal is, the more metallic. Reactivity increases when you go down the periodic table (vertical)
- ionization energy is the energy required to remove valence electrons from an atom. - this means that nonmetals have a higher ionization energy - metals have lower ionization energy b/c little energy is needed to remove electrons - the more protons, the higher the ionization energy
- Electronegativity is the atom’s ability to attract electrons (the chart below is the same for ionization energy)

Lewis Diagrams:
- shows only the valence electron

ionic compounds:

covalent compounds:

REMEMBER!
- ionic compounds conduct electricity when dissolved in water, or in molten form (it’s liquid state)
- covalent compounds cannot conduct electricity because they don’t have free electrons to carry the electricity. clevage: when you break a structure w/ enough pressure and it’ll break into a smooth flat surface. octect rule: atoms bond in order to get a full valence electron shell

Polarity of molecule:
- a bond is polar when the two atoms have two very different electronegativities but not enough to