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Atoms Notes (Foldable)
Law of Conservation of Mass Lab: Matter cannot be created or destroyed.
Reactants
Products
CaCl2 + Na2SO4 → CaSO4 + 2NaCl
A
+ B
→
C
+ D
300.23grams = 300.23grams
Law of Definite Proportions: A given chemical compound always contains the
same proportion by mass of its constituent elements. We show the law of
definite proportions by writing correct chemical formulas (H20, CO2, SO3...)
 27.0 grams of HgO will produce 25.0 grams of mercury and 2.0 grams of
oxygen.
 54.0 grams of HgO will produce 50.0 grams of mercury and 4.0 grams of
oxygen.
Law of Multiple Proportions: Multiple compounds can form from the same
elements.
 H2O and H2O2 are both compounds containing hydrogen and oxygen
atoms.
Dalton Proposed the 1st Atomic Theory
Electron 1st subatomic particle discovered by Thomson (Plum Pudding Model)
Proton (along with nucleus) 2nd subatomic particle discovered by Rutherford
(Gold Foil Experiment)
Neutron 3rd subatomic particle discovered by Chadwick
Nuclear Symbol Notation:
A charge
A = Mass Number = #protons + #neutrons
X
X = symbol from periodic table
Z
Z = Atomic Number = #protons (identifies the atom)
Charge = #protons - #electrons
(Atoms do NOT have a charge, ions do have a charge.)
Example Atom:
27
Al
13
Example Ion:
27 3+
Al
13
Hyphen Notation (atoms only):
Name or Symbol - A
Example Atom: Aluminum-27
Practice: How many electrons, protons, and neutrons are present in
Potassium-39?
Isotopes: atoms with the same atomic # but with a different mass # or a
different # of neutrons. Example:
Name in
Hyphen
Notation
H– 1
Number
of
protons
1
Number of
electrons
Number of
neutrons
Mass
Number
1
0
1
H–2
1
1
1
2
H–3
1
1
2
3
Nuclear
Symbol
Notation
Ions: when an atom has lost or gained electrons it becomes an ion. Ions have
either a positive or negative charge. Atoms do not have a charge because in an
ATOM the #protons = #electrons.
To calculate the charge of an ion = #protons - #electrons
Example: Write the nuclear symbol for an ion with 10 electrons, 11 protons,
and 12 neutrons.
When solving problems go to the MOLE!
Avogadro’s #
Molar Mass
Example: Write the nuclear symbol for an ion with 18 electrons, 16 protons,
and 16 neutrons.
Average Atomic Mass: the weighted average of the masses of all the isotopes
of that element. The average atomic mass of an element is reported on the
periodic table. A weighted average reflects both the mass and the abundance
of the isotopes as they occur in nature.
isotope
Atomic mass
abundance (%)
H-1
1.0078amu
99.985%
H-2
2.0141amu
0.015%
H-3
3.0160amu
negligible
The average atomic mass of hydrogen is 1.0079amu.
Multiply each atomic mass by the percent abundance and add them up
(1.0078amu)(.99985) + (2.0141amu)(0.00015) = 1.0079amu
Example: Three isotopes of argon occur in nature – Ar-36, Ar-38, Ar-40.
Calculate the average atomic mass of argon to two decimal places, given the
following relative atomic masses and abundances of each of the isotopes: Ar-36
(35.97amu; 0.337%), Ar-38 (37.96amu; 0.063%), and Ar-40 (39.96amu;
99.600%).
Mole Problems:
Example 1: ?g O2 → 25.0mol
Example 2 ?mol H2O→ 3.29X1025 molecules
Example 3 ?atoms Cu→ 107.1g