Transcript Atoms and Moles - Belle Vernon Area School District

Atoms and Moles – Chapter 3
Substances are made of
atoms 3.1
Atomic Theory
Atomic Theory – Atoms are the
building blocks of all matter.
Research into this theory led to
three laws that all compounds
share…
What does an atom look like?
Law of Definite Proportions
A given compound contains the
same elements in exactly the
same proportions by mass,
regardless of the size of the
sample or the source of the
compound.
Law of Definite Proportions
 Sodium chloride is
an example. All
samples of pure
NaCl will be 39.34%
Na by mass and
60.66% Cl by mass
no matter where the
NaCl comes from.
Sodium Chloride
Chlorine
Sodium
Law of Conservation of Mass
The mass of the products of a
reaction equals the mass of the
reactants.
Applies when elements combine to
produce a compound, decompose,
or when atoms in a compound
rearrange.
Law of Conservation of Mass
S
32.07
amu
+
+
O
O O
32.00
amu
S
O
64.07
amu
E=mc²
When you combine sulfur and
oxygen, 296,800 J of energy are
given off as heat.
According to E=mc²…
296,800kg•m²/s² = m(2.998 x 108m/s)²
Rearranging this equation gives the
mass to be 3.302 x 10-12 kg
Where does this mass go?
The Law of Multiple Proportions
States that the mass ratio for
one of the elements in a
compound that combines with a
fixed mass of another element
can be expressed in small
whole numbers.
Dalton’s Atomic Theory
Dalton used the three laws.
Elements and compounds
differ b/c of the types of
atoms.
Properties differ because of
atoms.
His Theory
Dalton proposed 5 principles
that make up his theory on
the atomic structure of
matter.
Dalton’s Five Principles
1.
All matter is composed of
extremely small particles called
atoms, which cannot be subdivided,
created, or destroyed.
2. Atoms of a given element are
identical in their physical and
chemical properties.
Dalton’s Five Principles
3. Atoms of different elements
differ in their physical and
chemical properties.
4. Atoms of different elements
combine in simple wholenumber ratios to form
compounds.
Dalton’s Last Principle
5. In chemical reactions atoms
are combined, separated, or
rearranged, but never
created, destroyed, or
changed.
Are they still true?
At the time, this explained
the chemical data that they
had.
Two invalid principles.
Is it still a theory?
Concept Check
According to Dalton, what is
the difference between an
element and a compound?
What are the five principles
of Dalton’s atomic theory?
Atomic Mass
Atomic Mass – the mass of an
atom in atomic mass units (amu)
Averages
Atoms of an element have
different masses.
AKA: the Dalton (Da)
The mass of C is 12.011 amu
The mole!
The mole is
the SI unit for
amount.
Why the
mole?
6.023 x 1023
THE MOLE!
Based on an isotope of carbon.
A mole is exactly the number
of atoms in 12 grams of the
carbon-12 atom.
Mole
1 mole of atoms of any element
has a mass in grams that is
equal to the atoms mass in
amu’s.
18.9984 amu of F = 18.9984
g/mol of F
Avogadro's Number
6.022 x 1023 is Avogadro’s #.
It’s the # of particles in 1 mole.
If 6 billion people were to count the
atoms in 1 mole, it would take them
over 3 million years to count them
all if counting at the rate of 1
atom/second.
Section Review
Complete the section review on
page 81. Do problems 1-7.