CHEM 090 Lecture Notes - Lecture 2: Atomic Number, Mass Number, Bromine
Chemistry 90 Chapter 2 Lecture Notes
ā¢ Molecules
o Heteroatomic: composed of different atoms
āŖ Ex: CO2, H2O
o Homoatomic: composed of the same atoms
āŖ Ex: P4
o Diatomic: made of 2 atoms (some molecules exist only as such)
āŖ Ex: N2, Cl2
o Polyatomic: made of many atoms covalently bonded, sharing overall charge
āŖ Ex: S4
ā¢ Atoms
o Atomic number = number of protons
o Mass number = number of protons + number of neutrons
o AZO A= atomic mass; Z= atomic # 168O
ā¢ Isotopes
o Same element, different mass
o Proton number cannot change; the difference comes from change in number of
neutrons
āŖ Ex: 3517Cl (17 protons, 18 neutrons, mass=35) vs. 3717Cl (17 protons, 20
neutrons, mass=37)
ā¢ Ions
o Atoms with charges: negative charge= gained electron; positive charge= lost
electron
Eī: Broī
µiī
¶e ā 7935Br (35 protons, 44 neutrons, 35 electrons, mass=79)
Eī: Nitrogeī
¶ ā 147N3- (7 protons, 7 neutrons, 10 electrons, mass=14)
Eī: Oīīgeī
¶ ā 168O2- (8 protons, 8 neutrons, 10 electrons, mass=16)
ā¢ Periodic Table
o Groups/ family: vertical columns, have similar properties
o Atomic weight: mass of average atom of an element expressed in atomic mass
unit (amu)
o Molecular weight: adding together all atomic weights of a molecule
Ex: CO2 = (12.011) + 2(15.9994) = 43.99
Ex: (NH4)3PO4 = 3(14.01) + 12(1.008) + 130.97 + 4(15.9994) = 149.1
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