Key Terms
Example
Al3+ and O2- combine as Al2O3. Two aluminums give 6+ total charge.
Law of Multiple Proportions
When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are
Conclusion
Atoms contain small, negatively charged particles. Called electrons.
Isotopes
Atoms of the same element that differ in the number of neutrons; same atomic number, different mass number.
Atomic Number (Z)
Number of protons in the nucleus. Defines the element.
Mass Number (A)
Total number of protons plus neutrons.
Neutral atom
Protons = electrons.
Ion
Protons do not equal electrons.
Written as
(mass number)(element symbol)(atomic number optional as subscript)
Reading
"Carbon-12" or "C-12."
Formula
Average atomic mass = sum of (isotope mass x fractional abundance) for each isotope.
Rule
Only the first letter is capitalized. Co = cobalt; CO = carbon monoxide compound.
Molecular Formula
Gives the exact number of each type of atom in one molecule. Example: C6H12O6 (glucose has 6 carbons, 12 hydrogens, 6 ox
Empirical Formula
Gives the simplest whole-number ratio of atoms.
Structural Formula
Shows which atoms are connected and how. Lines represent bonds.