Transcript The Mole - RC Schools

Atomic Mass and Intro to the Mole
 How do isotopes of the same element differ from each
other?
 To define atomic mass and to demonstrate how the
average atomic mass of an element is determined
 To introduce the concept of the mole
Atomic Mass
 Decimal number listed on the periodic table.
 Weighted average of all the naturally occurring
isotopes of that element.
 No atom has this exact mass.
 You will notice that the average atomic mass of an
element is often closest to the atomic mass of the most
abundant element.
 Chlorine has two naturally occurring isotopes,
chlorine-37 and chlorine-35. Which isotope is more
abundant? How do you know?
 The average atomic mass of an element depends on
both the mass and the relative abundance of each of
the element’s isotopes. Naturally occurring copper
consists of 69.15% copper-63, and 30.85% copper-65.
 To calculate the atomic mass, take the mass times the
decimal form of the percent abundance of each. Then
you add the numbers together to get the number that
appears on the periodic table.
Naturally occurring copper consists of 69.15% copper-63,
and 30.85% copper-65
0.6915 x 62.9296= 43.52
0.3085 x 64.9278= 20.03
63.55 (This is what appears on
the periodic table)
 Naturally occurring carbon consists of 98.93% carbon-
12 with an atomic mass of 12.00, and 1.07% carbon -13
with an atomic mass of 13.00. Calculate the atomic
mass.
An Introduction to Chemistry’s Favorite Number
 Imagine trying to count
all the grains of sand in
the castle
 Easier way:
 Count all the grains of
sand in 1 gram of sand
 Weigh all the sand and
convert using your
previous measurement
 Another easy way:
 Count all the grains of
sand in 1 liter of sand
 Measure the volume of
the sand and convert
using your previous
measurement
 Chemicals react in fixed
ratios at the atomic level
 In order to predict how
reactions will occur,
chemists need to know
how many atoms or
molecules they have
 Imagine you want to burn
the spoonful of sugar on
the right
 Every sugar molecule
reacts with a fixed number
of oxygen molecules
 In order to know how
much carbon dioxide and
water will be produced,
you need to know how
many molecules of sugar
you start with
 SI unit for amount of substance is called mole.
 A mole measures the number of particles
within a substance.
 A mole refers to a specific number of particles.
(Counting Unit)
 Particles can be atoms, ionic compounds, or
molecules
 1 mole = 6.02 x 1023 particles
 6.02 x 1023 is also known as Avogadro’s Number
1 mole aluminum = 6.02 x 1023 Al atoms
1 mole copper
= 6.02 x 1023 Cu atoms
1 mole lead
= 6.02 x 1023 Pb atoms
 Although 1 mole always contains the same number of
particles, the mass of one mole varies depending on
the substance.
 Molar Mass – mass of one mole of a substance.
 Mass of one mole of an element is equal to its
ATOMIC MASS expressed in grams.
 1 mole of aluminum
= 26.98 grams
 1 mole of copper
= 63.55 grams
 1 mole of lead
= 207.2 grams
 Molecular mass is the sum of the atomic masses of the
component elements
 H2O = 2 hydrogen, 1 oxygen = 2(1) + 1(16) = 18
 CH4 = 1 carbon, 4 hydrogen = 1(12) + 4(1) = 16
 NaCl = 1 sodium, 1 chlorine = 1(23) + 1(35) = 58
 1 mole of molecules will have a weight that equals the
molecular mass
 1 mol H2O = 18 g
 1 mol CH4 = 16 g
 1 mol NaCl = 58 g
Representative Particles and Moles
Substance
Representative
particle
Chemical
formula
Representative
particles in 1.00 mol
Copper
Atom
Cu
6.02 × 1023
Atomic nitrogen
Atom
N
6.02 × 1023
Nitrogen gas
Molecule
N2
6.02 × 1023
Water
Molecule
H2O
6.02 × 1023
Calcium ion
Ion
Ca2+
6.02 × 1023
Calcium fluoride
Formula unit
CaF2
6.02 × 1023