Chemistry Unit 2 Cheat Sheet

Unit 2: Atoms and Atomic Theory
Parts of an Atom: Calculations:
Proton(+1): determines the Proton: Atomic Number
element Neutron: Mass Number -
Neutron(0): Stabilizing Atomic Number
nucleus Charge: Protons - Electrons
Electron(-1): Determines
how the atoms bonds with Definitions:
other atoms Atomic Number: Number of protons in atom
Mass Number: Protons + Neutrons
Important Scientist: Isotope: Elements with different numbers of
Democritus: First to propose neutrons
the idea of an atom as an Isotopic Notation: “A” is the Mass
uncuttable piece of matter Number, “Z” is the Atomic Number
Marie Curie: Discovered and “X” is the element symbol
radioactivity
John Dalton: Proved atoms Average Atomic Mass:
existed Calculation:
JJ Thompson: Discovered Σ(relative abundance x mass of isotope)
electrons through the *REMEMBER to convert relative abundance
cathode ray tube percentage into a decimal(move 2 places)
Ernest Rutherford: and that this is a WEIGHTED AVERAGE*
Discovered the nucleus Example Problem:
through the gold foil Find the atomic mass of C-12 (98.9% abn.)
experiment and C-13 (1.1% abn.).
Niels Bohr: discover
electrons are located in (12x.989)+(13+.011) = 12.011
energy levels Answer: 12.011 amu
Erwin Schrodinger:
Introduced the idea of Types of Nuclear Decay:
electrons in space Penetration
Type: Symbol: Change:
James Chadwick: Power
Discovered the Neutron 4 Mass: -4
Alpha 2
He Atomic Number: -2 Low

0 Mass: No Change
Beta -1
e Atomic Number: +1 Medium

0 No Change
Gamma 0
y High