September 30th
Hand out tests
Periodic table:
Bohr shells; marble model
Outer shell is where the action is. Outer shell electrons are the ones
involved in bonding. The driving force behind bonding is the greater
stability of a full outer shell.
We call the outer shell electrons "valence electrons" (sec. 3.8).
Periodic table:
- Mendeleev
- Gaps: gallium
- First by atomic weights
- Later by atomic number
Bohr shells; marble model
Outer shell is where the action is. Outer shell electrons are the ones
involved in bonding. The driving force behind bonding is the greater
stability of a full outer shell.
We call the outer shell electrons "valence electrons" (sec. 3.8).
Chemical formulas
A chemical formula shows the elements in a compound and
their relative proportions in that compound.
A# of A B# of B C# of C
Note: when the number is "1", we just don't put it in.
The formula is for a unit, and changing any part of the formula
changes the compound: e.g. water to hydrogen peroxide.
Parentheses indicate that the stuff inside the parentheses is a unit.
A number after and below the closing parenthesis indicates
multiples of the unit inside the parentheses.
their relative proportions in that compound.
A# of A B# of B C# of C
Note: when the number is "1", we just don't put it in.
- Table salt: NaCl
- Carbon monoxide: CO
- Carbon dioxide: CO2
- Water: H2O
- Hydrogen peroxide: H2O2
- Monosaccharide sugars: C6H12O6
The formula is for a unit, and changing any part of the formula
changes the compound: e.g. water to hydrogen peroxide.
Parentheses indicate that the stuff inside the parentheses is a unit.
A number after and below the closing parenthesis indicates
multiples of the unit inside the parentheses.
- Mg(CO3)
- Li2(SO4)
- Ca(HCO3)2
- Ga(NO3)3
You can put a number in front of a formula (a "coefficient") to
indicate multiple units.