Download Symbols of Elements

Chapter 4 Lecture
History of the Atomic Model
Basic Chemistry
Fifth Edition
Chapter 4
Atoms and Elements
4.3 The Atom
• Democritus (400 B.C.)
• Believed that matter was composed of
invisible particles of matter he called
atoms.
• Antoine Lavoisier (1700’s)
• Law of Conservation of Mass – Matter
is not created or destroyed.
• Joseph Proust (1700’s)
Learning Goal Describe the electrical charge and
location in an atom for a proton, a neutron, and an
electron.
History of the Atomic Model
• John Dalton (Late 1700’s)
• First atomic theory explaining chemical reactions
• Law of constant composition –
compounds are composed of atoms in
definite ratios.
History of the Atomic Model
• Henri Bacquerel (1896)
• While studying the effect of x-rays on
photographic film, he discovered some
chemicals spontaneously decompose and
give off very penetrating rays.
• J.J. Thomson (1897)
• Discovered the electron using cathode
ray tubes.
• Proposed the Electron Cloud model, or
more commonly called the “Plum
Pudding” model
Thomsen’s “Plum Pudding”
Model of the Atom
J.J.Thomsen
• discovered that cathode rays
were streams of small
negatively charged particles
called electrons
• proposed the “plum pudding”
model of an atom in which
protons and electrons were
distributed throughout the
atom
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History of the Atomic Model
• Marie Curie (1898)
• Studied uranium and thorium and called
their spontaneous decay process
"radioactivity,” leading Rutherford to
discover the alpha particle.
• Hantaro Nagaok (1903)
• Postulated a "Saturnian" model of the
atom with flat rings of electrons revolving
around a positively charged particle.
• Robert Millikan (1909)
• Found the charge and mass of the electron
in his famous “oil-can” experiment.
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Milikan Oil Drop
Experiment (1909)
History of the Atomic Model
• Ernest Rutherford (1911)
• Discovered the nucleus in his famous
“gold foil” experiment.
• Using voltage and change
in the rate of fall of
charged oil drops, he was
able to determine the
charge on each drop.
• From Thompson’s charge
to mass ratio, Milikan
determined the charge and
mass of an electron.
Particles of Radioactivity
• Three types of radiation were discovered by
Ernest Rutherford:
  particles
  particles
  rays
Rutherford’s Gold Foil
Experiment (1911)
Since some particles
were deflected at large
angles, Thompson’s
model could not be
correct.
• Data from his experiments led
Rutherford to propose a planetary
model in which a cloud of electrons
surrounded a small, compact nucleus
of positive charge. Only such a
concentration of charge could produce
the electric field strong enough to cause
the heavy deflection of alpha particles
observed.
Rutherford’s Gold Foil
Experiment (1911)
Ernest Rutherford
shot  particles at
a thin sheet of
gold foil and
observed the
pattern of scatter
of the particles.
James Chadwick (1932)
Further developed the
atomic model by theorizing that
alpha and beta radiation results
from the decomposition of a
neutral particle found in the
nucleus, the neutron
• H atoms - 1 p; He atoms - 2 p
• mass He/mass H should = 2
• measured mass He/mass H = 4
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Subatomic Particles
Atoms contains subatomic particles:
• protons have a positive (+)
charge
• electrons have a negative (-)
charge
• like charges repel and unlike
charges attract
• neutrons are neutral
Structure of the Atom
An atom consists
• of a nucleus that contains protons and neutrons
• of electrons in the large empty space around the
nucleus
In an atom, the protons and
neutrons are in the nucleus,
whereas the electrons are
contained in the large space
outside the nucleus.
Like charges repel, and unlike
charges attract.
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Atomic Mass Scale
•
•
•
•
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Particles in the Atom
On the atomic mass scale for subatomic
particles,
1 atomic mass unit (amu) is equal to 1/12 of
the mass of the carbon-12 atom
a proton has a mass of 1.007 amu
a neutron has a mass of about 1.008 amu
an electron has a very small mass of
0.00055 amu
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Chapter 4 Lecture
Learning Check
Basic Chemistry
Fifth Edition
Is each of the following statements true or false?
A. The mass of an electron is greater than the mass
of a proton.
B.
Protons have a positive charge, and electrons
have a negative charge.
C.
The nucleus of an atom contains only the protons
and neutrons.
Chapter 4
Atoms and Elements
4.4 Atomic Number and
Mass Number
Learning Goal Given the atomic number and the mass
number of an atom, state the number of protons,
neutrons, and electrons.
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Atomic Number
Atomic Numbers and Protons
The atomic number
• is specific for each element
• is the same for all atoms of an element
• is equal to the number of protons in an atom
• appears above the symbol of an element
11
Na
Atomic Number
Symbol
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Learning Check
B. A sulfur atom
1) 32 protons 2) 16 protons
3) 6 protons
C. A barium atom
1) 137 protons 2) 81 protons
3) 56 protons
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• Hydrogen has atomic number 1, every H atom
has one proton.
• Carbon has atomic number 6, every C atom
has six protons.
• Copper has atomic number 29, every Cu atom
has 29 protons.
• Gold has atomic number 79, every Au atom
has 79 protons.
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Electrons in an Atom
State the number of protons in each atom.
A. A nitrogen atom
1) 5 protons
2) 7 protons
3) 14 protons
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Examples:
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An atom of any element
• is electrically neutral; the net charge of an atom is
zero
• the number of protons is equal to the number of
electrons
Example:
An atom of aluminum Group 3A (13) has 13 protons
and 13 electrons. It has a net charge of zero.
13 protons (13 +) + 13 electrons (13 -) = 0
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Mass Number
Learning Check
The mass number
• represents the number of particles in the nucleus
• is equal to the
Number of protons + Number of neutrons
An atom of zinc has a mass number of 65.
A. How many protons are in this zinc atom?
1) 30
2) 35
3) 65
B. How many neutrons are in the zinc atom?
1) 30
2) 35
3) 65
C. What is the mass number of a zinc atom that
has 37 neutrons?
1) 37
2) 65
3) 67
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Chapter 4 Lecture
Learning Check
Basic Chemistry
Fifth Edition
An atom has 14 protons and 20 neutrons.
Chapter 4
A. Its atomic number is
1) 14
2) 16
3) 34
Atoms and Elements
4.5 Isotopes and Atomic Mass
B. Its mass number is
1) 14
2) 16
3) 34
2) Ca
3) Se
C. The element is
1) Si
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Learning Goal Determine the number of protons, neutrons,
and electrons in one or more of the isotopes of an element;
calculate the atomic mass of an element using the percent
abundance and mass of its naturally occurring isotopes.
Isotopes
Nuclear Symbol
Isotopes
A nuclear symbol
• are atoms of the same element that have
different mass numbers
• represents a particular atom of an element
• have the same number of protons, but different
numbers of neutrons
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• gives the mass number in the upper left corner
and the atomic number in the lower left corner
Example: An atom of magnesium with an atomic
number of 12 and a mass number of 24 has the
following atomic symbol:
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Information from Nuclear
Symbols
Learning Check
• The nuclear symbol indicates the number of
protons (p+), neutrons, (n), and electrons (e -) in
a particular atom.
Naturally occurring carbon consists of three
isotopes, 12C, 13C, and 14C. State the number of
protons, neutrons, and electrons in each of the
following.
16
31
8
15
O
8 p+
8n
8 e-
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P
15 p+
16 n
15 e-
65
30
Zn
30 p+
35 n
30 e-
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12C
6
13C
6
6
protons
______
neutrons
______
______
______
electrons ______
______
______
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______
14C
______
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Learning Check
Learning Check
Write the nuclear symbols for atoms with the
following subatomic particles:
A. 8 p+, 8 n, 8 e-
___________
B. 17 p+, 20 n, 17e-
___________
1. Which of the following pairs are isotopes of the
same element?
2. In which of the following pairs do both atoms have
8 neutrons?
A.
15X
8
C. 47 p+, 60 n, 47 e-
___________
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12X
C.
15X
16X
7
8
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B.
6
31
15X
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14X
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Isotopes of Magnesium
Atomic Mass
The atomic mass of an element
• is listed below the symbol of each
element on the periodic table
11
Na
22.99
In naturally occurring magnesium,
there are three isotopes.
• gives the mass of an “average” atom
of each element compared to 12C
• is not the same as the mass number
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Examples of Isotopes and Their
Atomic Masses
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Calculating Atomic Mass
The calculation for atomic mass requires the
Most elements
have two or more
isotopes that
contribute to the
atomic mass of
that element.
• percent(%) abundance of each isotope
• atomic mass of each isotope of that element
• sum of the weighted averages
mass isotope(1) x (%) + mass isotope(2) x (%) + …
100
100
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Atomic Mass of Magnesium
Calculating Atomic Mass
Isotope Mass
The atomic mass of Mg
• is due to all the Mg
isotopes
• is a weighted average
• is not a whole number
Abundance
24Mg
= 23.99 amu x 78.70/100
25Mg
= 24.99 amu x 10.13/100
= 2.531 amu
26Mg
= 25.98 amu x 11.17/100
= 2.902 amu
= 18.88 amu
Atomic mass (average mass) Mg
= 24.31 amu
Mg
24.31
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Learning Check
__________
B. aluminum
__________
C. lead
__________
D. barium
__________
E. iron
__________
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Atomic Mass for Cl
Using the periodic table, specify the atomic mass of
each element:
A. calcium
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• The atomic mass of
chlorine is the
weighted average of
two isotopes 35Cl and
37Cl.
Chlorine, with two naturally occurring
isotopes, has an atomic mass of 35.45.
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Calculating Atomic Mass for
Cl
35Cl
has atomic mass 34.97 (75.76%) and
37C
atomic mass 36.97 (24.24%).
• Use the atomic mass and percent of each
isotope to calculate the contribution of each
isotope to the weighted average.
34.97 x 75.76 = 26.49 amu
100
35.97 x 24.24 =
8.962 amu
100
35.45 amu
has
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Learning Check
Gallium is an element found in lasers used in
compact disc players. In a sample of gallium,
there is 60.11% of 69Ga (atomic mass 68.93)
atoms and 39.89% of 71Ga (atomic mass 70.92)
atoms.
What is the atomic mass of gallium?
• The sum is the weighted average or atomic
mass of Cl. 35.45 amu
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