Counting Atoms

Atoms
Atomic Number (z) – Number of Protons
 In neutral atom – Number of Electrons
 Mass Number = Protons + Neutrons
 Isotopes – Same Element/Different Number of
Neutrons – still have same chemical behavior

Name
Protons
Neutrons
Electrons
Abundance
Protium
1
0
1
99.985%
Deuterium
1
1
1
0.015%
Tritium
1
2
1
Trace

Two Forms

Hyphen notation
 Element’s name – Mass Number
 Carbon – 14

Symbol Notation
 Ex.
 Ex.
MassNumber
AtomicNumber
ElementSymbol
14
6
C


How many protons, neutrons and electrons are
in Carbon -13?
What is the symbol notation for Oxygen-16?




Standard is Carbon-12 – mass is 12.00 atomic
mass units (amu)
Hydrogen – 1 is 1.007825 amu
Oxygen – 16 is 15.994915 amu.
Used for the masses of single atoms


Most Elements exist as a mixture of isotopes.
Separate isotopes and find abundance with a mass
spectrometer



Used in most calculations
Found on the Periodic Table
Calculated by:
AverageAtomicMass  ( MassIsotop e1 )  ( AbundanceIsotope1 ) 
( MassIsotop e2 )  ( AbundanceIsotope2 )  ........
Isotope

Mass (amu)
Abundance
Product
Oxygen-16
15.96
99.762%
15.957 amu
Oxygen-17
17.00
0.038%
0.0065 amu
Oxygen-18
18.00
0.200%
0.0360 amu
Total
16.00 amu
Note:


Abundance must be a decimal for the calculations
Always use atomic mass to 2 decimal places!!!!



Mole – the amount of substance which contains
the same number of particles as in 12 g of
Carbon – 12.
Avogadro’s Number – 6.022 x 1023 particles in a
mole (Just a number like dozen, gaggle, gross
or ream
Molar mass – the mass of one mole of a pure
substance – grams/mole. Numerically
equivalent to the atomic mass but in grams
rather than amu.

What is the mass in grams of 3.6 moles of C?

How many moles of Cu are in 3.22 g of Cu?


How many moles of C are in 2.25 x 1022 C
atoms?
How many moles of O are in 2,000,000 atoms of
O?


What is the mass in grams of 5.0 x 109 atoms of
Ne?
How many atoms of C are in 0.020 g of C?

How many grams of Ag contain the same
number of atoms as 10.0 g of B?