Download Chemistry Atoms Learning Objectives Atoms Essential knowledge

Chemistry
Atoms
Learning Objectives Atoms
Essential knowledge and skills:
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Determine the atomic number, atomic mass, the number of protons, and the number of electrons of any atom of a
particular element using a periodic table.
Determine the number of neutrons in an isotope given its mass number.
Perform calculations to determine the “weighted” average atomic mass.
Perform calculations involving the half-life of a radioactive substance.
Differentiate between alpha, beta, and gamma radiation with respect to penetrating power, shielding, and composition.
Differentiate between the major atom components (proton, neutron and
electron) in terms of location, size, and charge.
Identify key contributions of principal scientists including:
atomos, initial idea of atom – Democritus
first atomic theory of matter, solid sphere model – John Dalton
discovery of the electron using the cathode ray tube experiment, plum pudding model – J. J. Thomson
discovery of the nucleus using the gold foil experiment, nuclear model – Ernest Rutherford
discovery of charge of electron using the oil drop experiment – Robert Millikan
energy levels, planetary model – Niels Bohr
periodic table arranged by atomic mass – Dmitri Mendeleev
periodic table arranged by atomic number – Henry Moseley
quantum nature of energy – Max Planck
uncertainty principle, quantum mechanical model – Werner Heisenberg
wave theory, quantum mechanical model – Louis de Broglie.
Differentiate between the historical and quantum models of the atom.
Essential understandings:
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The periodic table is arranged in order of increasing atomic numbers.
The atomic number of an element is the same as the number of protons. In a neutral atom, the number of electrons is
the same as the number of protons. All atoms of an element have the same number of protons.
The average atomic mass for each element is the weighted average of that element’s naturally occurring isotopes.
The mass number of an element is the sum of the number of protons and neutrons. It is different for each element’s
isotopes.
An isotope is an atom that has the same number of protons as another atom of the same element but has a different
number of neutrons. Some isotopes are radioactive; many are not.
Half-life is the length of time required for half of a given sample of a radioactive isotope to decay.
Electrons have little mass and a negative (–) charge. They are located in electron clouds or probability clouds outside
the nucleus.
Protons have a positive (+) charge. Neutrons have no charge. Protons and neutrons are located in the nucleus of the
atom and comprise most of its mass. Quarks are also located in the nucleus of the atom.
Discoveries and insights related to the atom’s structure have changed\ the model of the atom over time. Historical
models have included solid sphere, plum pudding, nuclear, and planetary models. The modern atomic theory is called
the quantum mechanical model.
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History of the Atom (find answers from Power point in VISION)
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Democritus proposed: _______________________________________________________________
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These “particles” were thought to be indivisible
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Which person did not accept Democritus’ atom, he was of the “_______________ ________________”
philosophy
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Because of Aristotle’s popularity his theory was adopted as the standard
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By the 1700’s nearly all chemists had accepted the modern definition of an element as a
__________________________________________.
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It was also understood at that time that _______________________________
____________________________________________________________ However, these understandings
were based on ______________________ not ______________________ (empirical = comes from
observation)
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There was controversy as to whether elements always combine in the same proportion when forming a
particular compound.
In the 1790’s, chemistry was revolutionized by a new emphasis ____________________ because of new and
improved ________________.
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This new technology led to the discovery of some new scientific understandings
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The ___________________________________________:
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Proposed by Antoine Lavoisier
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States that
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Which means the _______________________________________________
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The _______________________________:
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The fact that a _______________________________________
______________________________________________________________________________________
______________________
Ex: ________, _________, _________, _______
Atomic Theory:
In 1808, John Dalton proposed an explanation for each of the proposed laws
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He reasoned that ___________________________________________
_________________________________________________________
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His ideas are now called the __________________________________
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All matter is composed of extremely small particles called _________
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Atoms of a given element are identical in ________, _______, and other properties; atoms of
______________ elements differ in size, mass, & other properties
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Atoms cannot be __________________, _________________, or________________
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Atoms of different elements combine in simple __________________________ to form chemical
compounds
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In chemical reactions, atoms are _____________, _____________, ____________________.
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Through these statements, evidence could be gathered to confirm or discount its claims
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Not all of Dalton’s claims held up to the scrutiny of experimentation
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Atoms _________ be divided into even smaller particles
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Not every atom of an element has an _____________.
Ex:
Dalton’s Atomic Theory of Matter has been modified.
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What remains is:
___________________________________________________________________________
___________________________________________________________________________
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One of the disputed statements of Dalton was that atoms are ________ indivisible
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In the 1800’s it was determined that
__________________________________________________________ like
_____________________________________________________________________
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It’s the _______________ and ________________ of these particles that determine the atom’s chemical
properties.
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The definition of an atom that emerged was:
______________________________________________________________________________________
__________________________________________________________
Structure of an Atom
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All atoms consist of 2 regions that contain the subatomic particles
________________________________________________________________
________________________________________________________________
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The nucleus is a very small region located near the center of the atom
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In every atom the nucleus contains at least 1 _________, which is _________________ charged particle
and usually contains 1 or more _______ particles called __________.
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The electron cloud is the region that surrounds the nucleus
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This region contains 1 or more _______________, which are _______________ charged subatomic
particles
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The volume of the electron cloud is ____________________ than the nucleus
Discovering the Electron
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The discovery of the first subatomic particle took place in the late 1800’s.
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A power source was attached to two metal ends of an evacuated glass tube, called a
______________________________.
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A beam of “light” appears between the two electrodes called a _________________
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Investigators began to study the ray and they observed that…
An object placed in the path of the ray cast a shadow on the glass
Cathode rays were _________________________________________
The rays were deflected away from a __________________________.
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The first 2 observations support the idea that the ray is composed of ________
_______________________________________________________________
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The second set of observations support the evidence that the ray is composed of a
_________________________________________________________________.
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J.J. Thomson studied the rays with cathode tube and proved that they were
____________________________ being emitted from the metal atoms. Dubbed these tiny particles
“___________”
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Devised the________________________ Model
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Each atom was a sphere filled with a _________________________. The fluid was called the "______."
Scattered in this fluid were __________ known as the "_________."
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Robert Millikan then used an ingenious investigation to calculate
___________________________________________________________________
In his Oil Drop Experiment, he determined that
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______________________________________________
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Charge of Electron= ______________________________
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Mass of Electron = _______________________________
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What can their work help us conclude about the atom?
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atoms are composed of smaller particles, and one of these components is
________________________________
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atoms are neutral, so there must be an opposing _____________________
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because electrons are essentially mass-less, there must be an
__________________________________________________________________
Discovering the Neutron
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In 1932, the English physicist James Chadwick discovered yet another subatomic particle.
–
the ____________________ is electrically neutral
–
It’s mass is nearly _________________as that of the proton
New Structure of Atoms
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In 1911, Ernest Rutherford et al. provided a more detailed picture of the internal structure of the atom
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Gold Foil Experiment: In his experiment, Rutherford directed a narrow beam of __________________
at a very thin sheet of ______________.
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Alpha particles (α) are _______________________________________.
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According to Thomson’s model, the heavy, positive alpha particles
______________________________________________________________________________________
__________________________________________________________
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However, Rutherford found _________________________________________________
________________________________________________________________________
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Rutherford suggested a new structural model of the atom.
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He stated that ________________________________________
___________________________________________________
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And that the atom is mostly ____________________________.
___________________________________________________ like planets around the sun.
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Rutherford’s planet system model was an improvement over earlier models, but it was still not complete.
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Physics says that _________________________________________
_______________________________________________________
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Losing energy would cause the electron to spiral into the nucleus.
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The attraction of the electron to the nucleus would cause it to spiral into the nucleus as well
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Niels Bohr proposed a new model that would allow the _______________________________________
and _________________________
____________________________________________________________________.
His model coupled Rutherford’s model with a new concept of energy in Physics called
_____________________________________________________________________
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Bohr proposed that the electrons aren’t on any random orbit around the nucleus, they are on
_________________.
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Bohr’s Model restricts the orbits on which an electron can be found
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The bases for what orbit an electron is allowed is entirely based on
_________________________________________
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If it has any more energy or any less energy it would be forced to be on a different path of different energy
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Each path or level of energy that the electron is on is given a label of “n”
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Such that n=1 is the closest energy level to the nucleus
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Each energy level can only hold a certain number of electrons (2n 2)
n=1 can hold ____ electrons
n=2 can only hold ____ electrons
n=3 can hold ____ electrons
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Summary of the main ideas in chronological oder
NAME
CONTRIBUTION
Atomic Theory:
1.
JOHN DALTON
2.
3.
4.
5.
All matter is made
of atoms (atoms are
indivisible and
indestructible)
All atoms in an
element are
identical to each
other in mass and
properties
Compounds are
formed by a
combination of 2 or
more different kinds
of atoms in different
ratios
A chemical reaction
is a rearrangement
of atoms
In reactions, matter
is neither created or
destroyed (law of
conservation of
matter)
MODEL OR EXPERIMENT
Solid Sphere – “Billiard Ball Model”
-different atoms were drawn at
different sizes
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J. J. THOMSON
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ERNEST
RUTHERFORD
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NIELS BOHR
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Discovered
electrons
Used cathode rays
to show how
electrons were
deflected by
magnetic forces
Gold Foil
experiment –
proved nuclear form
Discovered a
positively charged
nucleus (99.9% of
mass of atom)
Atoms are mostly
made up of empty
space
Discovered electron
motion
Said that electrons
orbit around the
nucleus
Light emissions
- Negative electrons set in a sponge of
“+” charge
-“Plum Pudding” Model
- “Nuclear” Model
- Protons in nucleus with electrons
floating outside nucleus
- “Solar System” Model
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Subatomic Particles
In ancient times, people believed that all matter is a variation of earth, air, fire and water. Until early 20th century
people believed that the basic building block of matter is an atom, visualized as a sphere. Nowadays, we know that
atoms are made of even more fundamental entities. The diagram below shows an increasing magnification of an
imaginary microscope on an ordinary matter.
For a given atom, it is consisted of a nucleus occupies a very small volume of space, and a collection of electrons
that are attracted to the nucleus by electromagnetic forces. The lump is called the nucleus of an atom while the
extension of electrons in space defines the size of an atom. The more number of electrons the larger the size of the
atom. Electrons are incredibly small. No one knows the actual size, but it is estimated at the lower scale of 10 -18 m,
almost a point-like. Electrons are one of the most fundamental particles. In other words, they are not made of
anything smaller (so we think).
However, the nucleus is made of a mixture of protons and neutrons. The size of a proton and a neutron are similar,
in the order of 10-15 m. We now know that they are not the fundamental particles. Take, for example, a proton. It is
now believed a proton is made of three fundamental particles called quarks. There are six different types of quarks,
of which only up (u) quark and down (d) quark made up of protons: 2 up and 1 down. This is often written as 'duu'.
On the other hand, a neutron is made of 'ddu': two down quarks and one up quark. Once again, to our current
understanding, a quark is a fundamental particle. These quarks are held very tightly by the strong force carrier called
gluon.
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The Strong force
This force acts between quarks. Its operation involves the exchange of particles called gluons (which are neither
quarks nor leptons).
• The force does its work in a very short time (~ 10 -23s), so can bring about interactions between particles colliding
at high kinetic energies (and close to each other for only very short times).
The Weak force
Both quarks and leptons can ‘feel’ the weak force. It is involved in certain decays and interactions, and its
involvement – in all common cases – is signalled by
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interaction times in the order of 10-12 s or longer
neutrino (or antineutrino) involvement
change of quark flavour (that is u number and d number are not conserved)
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The Electromagnetic force
This acts between all charged particles and is signalled by photon emission or absorption. It may be involved in the
internal re-arrangement of, for example, quarks within a hadron, or electrons within an atom. Some particleantiparticle annihilations occur via this force. A typical interaction time would be 10 -17s.
Summary Table
Sub Atomic
Particle
Proton
Neutron
Electron
Mass (kg)
1.672 x 10-27
1.675 x 10-27
9.109 x 10-31
Relative Atomic
Mass (amu)
1
1
1/1840
Charge (C)
1.60 x 10-19
0
-1.60 x 10-19
Relative charge
(C)
+1
0
-1
Where?
nucleus
nucleus
clouds
Distinguishing Between Atoms
Atomic Number
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Elements are different because they contain different numbers of protons
The atomic number of an element is the number of protons in the nucleus
o Atomic number identifies an element
o Since atoms are neutral, number of protons = number of electrons
o The number of protons never changes for an element
o The number of electrons might change for an element (forms an ion)
o Elements on the periodic table are organized according to increasing atomic number, or increasing
number of protons
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Mass Number
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Total number of protons and neutrons in an atom is called the mass number
Number of neutrons can be determined by
o Number of neutrons = mass number – atomic number
Shorthand notation for an element
A
Z
X
X = Element symbol from the periodic table
A = Mass Number (p + n)
Z = Atomic Number (p)
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Usually abbreviate the names of the element by saying the name of the element followed by its atomic mass,
“carbon-12.”
Isotopes
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Isotopes are atoms of the same element that have different masses. The number of protons and electrons is the
same for all isotopes of an element, but the number of neutrons is different, causing each isotope to have a
different atomic mass. Atomic number does not change.
o Hydrogen-1 has no neutrons, mass number of 1
o Hydrogen-2 (deuterium) has one neutron, mass number of 2
o Hydrogen-3 (tritium) has two neutrons, mass number of 3
Isotopes are chemically alike because they have identical numbers of protons and electrons which are the
subatomic particles responsible for chemical behavior
Why can there be more than one possible number of neutrons in an atom? For many atoms, there can be several
different numbers of neutrons that serve to stabilize the positive charge in the nucleus.
Atomic Mass or Atomic Weight
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Atomic mass is measured in atomic mass units (amu), defined as 1/12 the mass of a carbon-12 atom. (Carbon12 is the standard reference.)
1 amu = 1.67 x 10-27 kg
Atomic mass is not always a whole number because of the relative abundance of the naturally occurring
isotopes of the element.
Most elements occur as a mixture of two or more isotopes
Each isotope of an element has a fixed mass and natural percent abundance
The atomic mass of an element is the weighted average mass of the atoms in a naturally occurring sample of
the element.
How to calculate atomic mass:
o Need the number of stable isotopes of the element
o The mass of each isotope
o The natural percent abundance of each isotope
Example:
Chlorine-35 occurs 75.77% (34.969 amu)
Chlorine-37 occurs 24.23% (36.966 amu)
Convert percentages into decimals (75.77% = 0.7577)
(0.7577 x 34.969) + (0.2423 x 36.966) = 35.453 amu
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Closer to the mass of Chlorine-35 since that’s the more abundant isotope. Note the correct number of
significant figures.
Atoms
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The number of protons in an atom determines the identity of the atom. Atomic number = number of Protons
In a neutral atom, the number of positive protons equals the number of negative electrons.
Protons and neutrons both have a mass of 1 amu. The mass of the electron is negligible compared to the mass
of the proton and neutron. Thus the mass number, or the mass of the atom, is the sum of the number of protons
and neutrons. Mass number = number of Protons + number of Neutrons
Name
Symbol
Atomic #
Mass #
# Protons
Selenium
# Neutrons
# Electrons
46
222
86
118
11
79
12
Isotopes
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The number of neutrons in any specific type of atom can vary. Atoms of the same element with different
numbers of neutrons are called isotopes.
Isotopes are distinguished from each other by including the mass number with the name or symbol.
Name
Symbol
Atomic #
Mass #
# Protons
# Neutrons
# Electrons
235
U
238
U
Carbon-12
Carbon-13
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Ions
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As we have seen, in a neutral atom, the number of protons and the number of electrons is equal.
Atoms can gain or lose electrons to become ions. Ions are charged atoms resulting from the difference in
number of positive protons and negative electrons.
A cation is a positive ion. A cation results when an atom loses electrons. Number of Protons > Number of
Electrons
An anion is a negative ion. An anion results when an atom gains electrons. Number of Electrons > Number of
Protons
Ions are distinguished from atoms by including the ion charge as a superscript in the symbol.
Name
Symbol
Atomic #
Mass #
# Protons
# Neutrons
Al3+
56
23
15
F-
&
Cation or
Anion?
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Ferric Ion
IS O TO P E S
# Electrons
15
18
19
A VE RA G E
A TO M IC
M A SS
1.
What is the average atomic mass of silicon if 92.21 % of its atoms have a mass of 27.977 amu, 4.07 % have a
mass of 28.976 amu, and 3.09 % have a mass of 29.974 amu?
2.
Calculate the average atomic mass for neon if its abundance in nature is 90.5% neon-20 (19.922 amu), 0.3%
neon-21 (20.994 amu), and 9.2% neon-22 (21.991 amu).
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3.
4.
Calculate the average atomic mass of chromium.
Isotope
Mass (amu)
Chromium – 50
49.946
Chromium – 52
51.941
Chromium – 53
52.941
Chromium – 54
53.939
Which of the following are isotopes of element X, with atomic number of 9? (Circle)
19
9
5.
Relative Abundance
0.043500
0.83800
0.095000
0.023500
X , 209 X , 189 X ,
21
9
X
The element Eu occurs naturally as a mixture of 47.82% 151Eu, whose mass is 150.9 amu and 52.18% 153Eu,
whose mass is 152.9 amu. Calculate the average atomic mass of Eu.
Atomic Structure Review
The table below contains information about several elements. In each case, enough information has been provided
for you to fill in the blanks. Assume all atoms are neutral.
Isotope name
6.
Nuclear
Symbol
Atomic
Number
Mass
Number
12
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# of
Electrons
# of
Neutrons
calcium-40
7.
1
8.
9.
# of
Protons
197
79
2
Au
26
10.
16
30
201
11.
17
12.
1.
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Please use the following table to calculate the average atomic mass of chlorine. Correct significant digits
required.
Isotope
% Abundance
Mass (amu)
35
75.78%
34.969
37
24.22%
36.966
Cl
Cl
2.
80
Raiderium (Cv) has three naturally occurring isotopes. Raiderium is 74.655% 44Cv, which has an atomic
mass of 43.064 amu, 24.958% 46Cv, which has a mass of 46.125 amu, and 0.387% 48Cv, which has an
atomic mass of 47.982 amu. Please calculate the average atomic mass of Raiderium to the correct number
of significant digits.
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Nuclear Chemistry: Types of Ionising Radiation
Mass
Type of
radiation
Alpha
radiation
Charge
g mol-1
+2
4
Nature
Symbol
2 protons
4
2𝐻𝑒
2 neutrons
Deflection in
magnetic or
electric fields
Relative
penetration
power
Some deflection
towards negative
plate
Paper or a few
centimetres of air
Large deflection
towards positive
plate
Aluminium plate
1-2 cm thick
No deflection
Lead 1 cm thick
or 2 m of concrete
(α particle)
helium nucleus
Beta
radiation
-1
1/1840
4
2𝛼
0
−1𝛽
high energy
electron
0
−1𝑒
(β particle)
Gamma
radiation
(  rays)
0
0
Short wavelength
electromagnetic
radiation
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0
0

Zone of Stability
Decay Series
Balancing Nuclear equations
The mass number and atomic number on either side of the reaction arrow must balance (conservation of mass). Use
your periodic table to find the missing element/sub-atomic particle
19
222
Rn
86
→
234
Th
90
→
230
Th
90
→
214
Pb
82
→
234
→
92
U
4
2He
+
4
2α
+
226
88Ra
+
+ −10e
234
Np
93
+
Write a balanced nuclear equation for the Beta decay of:
Nitrogen-16
Potassium-40
Write a balanced nuclear equation for the Alpha decay of:
Plutonium-244
Strontium-90
1.
Complete the following reactions:
39
17𝐶𝑙
→
26
14𝑆𝑖
→ ?+
226
88𝑅𝑎
0
+1𝑒
+ ?
+
1
0𝑛
→ ? + 42𝛼
? → 2 10𝑛 +
2.
25
15𝑃
236
92𝑈
Write correct nuclear equations for each of the following:
-232
20
positron (ß+ ) decay of zinc-65
b.
c. beta ( ß- ) decay of copper-64
d. electron-capture of potassium-40 (a “beta” particle being added as a reactant)
e. gamma decay of barium-137
3.
Complete the following nuclear equations. In each case write which type of decay is occurring.
131
53 I
67
31
11
6

Xe 
0
1
e
Ga  01 e  Zn
C  B  01 e
Tc  Tc   .
99m
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Fission and Fusion
Half-Life Calculations
The definition for half-life is the time required for half the original amount of substance to decay. This can be mass
or radiation count. In this unit we will only use whole number half-lives.
21
Number of Half-lives
0
1
2
3
4
5
Fraction remaining
1/2
1/4 (1/2 x 1/2)
1/8 (1/2 x ½ x ½ )
1/16 (1/2 x ½ x ½ x ½ )
?
% remaining
100
50
25
12.5
6.25
?
1. Barium-139 has a half-life of 86 minutes. Suppose you have a 17.8-gram sample of barium-139. How much of
the sample remains unchanged after 5 hours and 44 minutes?
2. A sample of cobalt-60 has a half-life of 5.26 years. If 98 grams of this radioisotope remain unchanged after
approximately 15.78 years, what was the mass of the original sample?
3. After one year and 124 days, approximately 150 grams of a sample of calcium-45 remain unchanged. If the
original sample had a mass of 1200 grams, what is the half-life of calcium-45? [The half-life will be in days.]
4. Phosphorus-33 has a half-life of 25.4 days. Suppose you have a 46.8- gram sample of phosphorus-33. How much
of the sample remains unchanged after 101.6 days?
More half-life Problems
How much of a 100.0 gram sample of gold-198 is left after 8.10 days if its half-life is 2.70 days?
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A 50.0 grams sample of nitrogen-16 decays to 12.5 grams in 14.4 seconds. What is its half-life?
The half-life of potassium-42 is 12.4 hours. How much of a 728 gram sample is left after 62.0 hours?
What is the half-life of technetium-99 if a 500.0 gram sample decays to 62.5 grams in 639,000 years?
The half-life of thorium-232 is 1.4 x 1010 years. If there are 25.0 grams of the sample left after 2.8 x 10 10 years, how
many grams were in the original sample?
There are 5.0 grams of iodine-131 left after 40.35 days. How many grams were in the original sample if its half-life
is 8.07 days?
Review Questions:
1)
Write the nuclear transformation reaction for the alpha decay of radon-198
2)
Write the nuclear transformation reaction for the beta decay of uranium-237
3)
Write the nuclear transformation reaction for the Positron emission from silicon-26
23
4)
Write the nuclear transformation reaction for Sodium-22 undergoing electron capture
5) Plutonium-239 has a half life of 2.41x104 yr. If you have a 1.00 mg sample how much will remain after 4 halflives have passed?
6) The half-life of 95Am241 is 458 years. How much of a 12.0 g sample would remain after 1375 years?
THE NUCLEAR FISSION REACTOR
The reactor is a way of getting energy from the uranium fission in a controlled way. The first nuclear fission reactor
was made by Enrico Fermi in a squash court in Chicago in 1942.
One form of fission reactor is shown in the diagram.
24
The CORE of the reactor contains the uranium fuel (an alpha emitter and not very dangerous if handled with care)
that is held in thousands of metal tubes in a large block of graphite. The graphite, called the MODERATOR slows
down the neutrons emitted at each fission so that they can react better. Carbon dioxide gas is blown through the reactor
core under pressure to take away the heat energy produced by the fission reactor. This gas is then passed over tubes
containing water, giving out its heat and turning the water into high temperature steam which is then used to drive
turbines and generators. To increase or decrease the output power of the reactor a large number of CONTROL RODS
are used. These are made of boron or boron-steel that gobble up neutrons. They can be lowered into the reactor to
reduce the number of neutrons and so lower the power or they can be raised to increase the power.
When the nucleus splits we get two smaller nuclei, two or three neutrons and some energy. This energy appears as
heat due to the kinetic energy of the smaller nuclei and the neutrons.
The energy is produced because the mass of the uranium nucleus plus the mass of the incoming neutron is slightly
greater than the masses of the particles formed after fission.
You don't get very much energy from splitting one uranium nucleus but in one kilogram of uranium there are around
a million million million million million nuclei and if you could split all of them the energy produced would be very
large. In fact if all the nuclei in 1 kg of uranium 235 could be split the energy produced would be about the same as
that obtained from burning three thousand tons of coal!
The whole reactor core is contained in a steel pressure vessel and then surrounded by a thick layer of concrete to
protect the workers from radiation.
The reactor is a very heavy structure and so it is important that nuclear power stations are built on very stable solid
rock.
They need large amounts of water to turn to steam to drive the turbines and also as coolant in the condensing units
and so they should be built near the sea, a river estuary or a large lake.
People are not usually too happy about living near a nuclear reactor and so nuclear power stations are usually built in
areas of low population.
Benefits and drawbacks of nuclear power
(a) benefits
(i) low or zero carbon dioxide emission
(ii) relatively large uranium fuel reserves
(b) drawbacks
(i) expensive to build
(ii) radiation danger during operation
(iii) danger of terrorist attack
(iv) disposal of radioactive nuclear waste
Nuclear waste
Low level waste: This is gloves, cast off clothing, over shoes etc.
Intermediate level waste: This is fuel containers
High level waste: This is mainly irradiated fuel taken from reactors.
Questions:
1.
This is a diagram of a typical nuclear reactor.
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(i)
Which part of the reactor is designed to control the rate of nuclear fission?
(ii)
The moderator slows down the neutrons. Why do they need slowing down?
Useful Radioisotopes
Radioactive isotopes can be very useful. They are used in:
1. Medicine for both treatment and diagnosis
2. Archaeological and geological dating using carbon-14 or uranium
3. Fluid flow measurement - water, blood, mud, sewage etc.
4. Thickness testing of materials such as polythene
5. Radiographs of metal castings
6. Sterilisation of food and insects
7. Tracers in fertilisers used in agriculture
8. Smoke alarms in houses
9. Tracing phosphate fertilisers using phosphorus-32
10. Checking the silver content of coins
11. Atomic lights using krypton-85
12. Testing for leaks in pipes
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Oxidation Numbers
Redox Reactions - Practice Problems - Determining Oxidation Numbers
1. Determine the oxidation number of each element in the following compounds.
Oxidation Numbers for each Element
a.
SnCl4
Sn
Cl
b.
Ca3P2
Ca
P
c.
SnO
Sn
O
d.
Ag2S
Ag
S
e.
HI
H
I
f.
N2H4
N
H
g.
Al2O3
Al
O
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h.
S8
S
i.
HNO2
H
j.
O2
O
k.
H3O+
H
O
l.
ClO3-
Cl
O
m.
S2O32-
S
O
n.
KMnO4
K
Mn
O
o.
(NH4)2SO4
N
H
S
N
2. Determine the oxidation number of carbon in each of the following compounds:
a. methane, CH4
b. formaldehyde, CH2O
c. carbon monoxide, CO
d.
carbon dioxide, CO2
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O
O