Download Atoms: The Building Blocks of Matter

Atoms: The Building
Blocks of Matter
Chapter 3
• Nature’s basic particle
is atom
• Based on the Greek
word for indivisible
• Did not believe in atoms
• Thought all matter was
continuous
• View held for almost 2000
years
Basic Laws of Chemistry
Law of Conservation of Mass – mass is
neither created nor destroyed in an ordinary
chemical or physical change
Law of Definite Proportions – chemical
compounds contain the same elements in
the same proportions regardless of the
sample
Law of Multiple Proportions – elements may
combine in small whole number ratios to
form different compounds
Dalton’s Atomic Theory - 1808
1. All matter is composed of tiny indivisible
particles called atoms
2. Atoms of a given element are identical.
Atoms of different elements differ in some
fundamental way.
3. Atoms cannot be subdivided, created, or
destroyed.
4. Atoms of different elements combine in
small whole number ratios to form
compounds
Dalton’s Atomic Theory
4. Atoms of different elements combine in
small whole number ratios to form
compounds
5. In chemical reactions, atoms are
combined, separated, or rearranged
Structure of the Atom
Discovery of the electron – 1897
Joseph John Thompson
Discovery of the Nucleus
Ernest Rutherford - 1911
Discovery of the Nucleus
Ernest Rutherford - 1911
Discovery of the Nucleus
Ernest Rutherford - 1911
The Nuclear Atom
The Nuclear Atom
Subatomic Particles
Particle
Electron
Proton
Neutron
Symbol
Relative
Charge
Mass
Number
Relative Mass
(amu)
Actual
Mass (kg)
0
−1𝑒
1
1H
1
0𝑛
-1
0
0.0005486
9.109 x 10-31
+1
1
1.007276
1.673 x 10-27
0
1
1.008665
1.675 x 10-27
Atomic Number
•
•
•
•
Atoms of different elements have different
numbers of protons
Atoms of the same element have the
same number of protons
Atomic # is the number of protons in the
nucleus of an atom
Defines the element
Isotopes
•
•
•
Atoms with the same number of protons
but different numbers of neutrons.
Show almost identical chemical properties;
chemistry of atom is due to its electrons.
In nature most elements contain mixtures
of isotopes.
Isotopes
Isotopes of Hydrogen
Isotope
Nuclear
symbol
Number of
protons
Number of
electrons
Number of
neutrons
Hydrogen-1
1
1H
2
1H
3
1H
1
1
0
1
1
1
1
1
2
Hydrogen-2
Hydrogen-3
Atomic Masses
Mass Spectrometer
Atomic Masses
Isotope
Atomic mass
(amu)
Hydrogen-1
1.007825
Hydrogen-2
2.014102
Hydrogen-3
3.016049
Average Atomic
Mass (amu)
1.00794
Atomic Masses
Isotope
Percent
abundance
Atomic mass
(amu)
Hydrogen-1
99.985
1.007825
Hydrogen-2
0.015
2.014102
Hydrogen-3
negligible
3.016049
Average Atomic
Mass (amu)
1.00794
Average Atomic Mass
The average atomic mass depends on
1. Mass of the individual isotopes
2. Relative abundance of each of the
element’s isotopes
Weighted average
Calculating Avg. Atomic Masses
Isotope
Percent
abundance
Atomic mass
(amu)
Hydrogen-1
99.985
1.007825
Hydrogen-2
0.015
2.014102
Hydrogen-3
negligible
3.016049
Average atomic
mass (amu)
1.00794
Avg. Mass = (0.99985*1.007825) + (0.00015*2.014102)
Avg. Mass = 1.0079
Calculating Avg. Atomic Masses
Isotope
Percent
abundance
Atomic mass
(amu)
C-12
98.90
12
C-13
1.10
13.003355
C-14
negligible
14.003242
Calculate the average atomic mass.
Avg. Mass = (0.9890*12) + (0.0110*13.003355)
Avg. Mass = 12.0111
Average atomic
mass (amu)
?
Calculating Avg. Atomic Masses
Isotope
Percent
abundance
Atomic mass
(amu)
Average atomic
mass (amu)
Cu-63
69.17
62.929599
?
Cu-65
30.83
64.927793
Calculate the average atomic mass.
Avg. Mass = 63.546
Average Atomic Mass
The average atomic mass reported on the periodic table
can be thought of from two points of view
• The very small – an average carbon atom weighs
12.01 amu
• The very large – one mole of carbon atoms weighs
12.01 g
Counting by Weighing
• In most experiments, atoms are much too small to
count individually
• The relative atomic mass scale makes it possible to
know how many atoms are present in a sample
without counting them
Counting by Weighing
• Represents the mass of one mole of
calcium atoms in grams
• 40.08 g of Ca = 1.000 mol Ca atoms
• 40.08 g of Ca = 6.02 x 1023 atoms
• 20.04 g of Ca = 0.5000 mol Ca
• 20.04 g of Ca = 3.01 x 1023 atoms
Counting by Weighing
• Use dimensional analysis for conversions between
grams, moles, and numbers of atoms.
Counting by Weighing
Perform the following conversions.
1. 0.357 mol gold = ? g
2. 10.0 g silicon = ? mol
3. 1 carbon atom = ? g
4. 20.0 g tungsten = ? atoms
Counting by Weighing
Perform the following conversions.
1. 4.0 x 1022 atoms of boron = ? mol boron
2. 1.5 x 10-3 mol sodium = ? atoms sodium
3. 3.5 x 10-2 g lithium = ? mol lithium
4. 4.25 g nickel = ? atoms nickel