Download Reporting Category 2: Atomic Structure and Nuclear Chemistry

Alief High School Chemistry STAAR Review
Reporting Category 2: Atomic Structure and Nuclear Chemistry
C.6.A
Understand the
experimental
design and
conclusions
used in the
development of
modern atomic
theory,
including
Dalton’s
Postulates,
Thomson’s
discovery of
electron
properties,
Rutherford’s
nuclear atom,
and Bohr’s
nuclear atom.
Atomic Theory
Scientist
Contribution to Modern Atomic Theory
Dalton
Dalton’s Postulates:
• Elements are made of very small, indivisible particles
called atoms.
• All atoms of a given element are identical.
• Atoms of a given element are different from those of any
other element and have different atomic masses.
• In a chemical reaction, atoms of one element can combine
with atoms of another element in whole-number rations
to form compounds.
• Chemical reactions change the arrangement of atoms, but
do not change atoms of one element into atoms of
another element.
Used cathode rays to estimate electron’s charge-to-mass ratio;
model known as “plum-pudding model”; described an atom as
electrons submerged in a positively charged substance, similar to
raisins stuck in dough.
Gold foil experiment proved the existence of a dense, charged
nucleus surrounded by electrons in mostly empty space; known as
the nuclear atom model.
Refined the nuclear atom model; electrons orbit the nucleus in
distinct, definite energy levels
Thomson
Rutherford
Bohr
The Modern Atomic Theory (also known as the Quantum Mechanical Model):
proposes that electrons travel throughout an electron cloud, a region of space
surrounding a nucleus that contains protons and neutrons.
C.6.B
Understand the
electromagnetic
spectrum and
the
mathematical
relationships
between
energy,
frequency, and
wavelength of
light.
Electromagnetic Spectrum
A wave can be described by its frequency, wavelength, and energy.
Vocabulary Words to
Know
Electromagnetic
spectrum
Wavelength
Definitions
Symbols/examples/SI units
Show wave types from
shortest wavelength to longest
wavelength; some show
longest wavelength to shortest
wavelength depending of
spectrum.
See diagram above
λ is
Distance between two
adjacent crests or troughs
the
symbol for wavelength.
SI unit: meters
Frequency
The number of waves that
pass a given point per unit of
time
f is the symbol for frequency used on
STAAR formula chart.
SI unit: Hertz
Waves/sec
Speed of light
Planck’s constant
All electromagnetic waves
travel at the speed of light in a
vacuum. The speed of light is
a constant value of 3.00 x
8
10 m/s.
German physicist Max Planck
determined a relationship
between energy and
frequency. He determined that
matter absorbs
electromagnetic radiation in
small, specific amounts, called
quanta. Planck’s constant has
-34
a value of 6.63 x 10 J● s
c is the symbol for speed of light.
SI unit: m/s
h is the symbol for Planck’s constant.
SI unit: J● s
What are the mathematical relationships between wavelength and
frequency?
All electromagnetic waves travel at the speed of light in a vacuum. The speed of light (c) is a constant
8
value of 3.00 x 10 m/s or 300,000,000 meters per second. The product of the wavelength and
frequency of a wave equals the speed of light.
c = λf
Frequency and wavelength are inversely proportional to each other. This means that as one increases,
the other decreases such that the product of the two is always the constant c.
What are the mathematical relationships between energy and
frequency?
Planck showed that the amount of radiant energy (E) of a single quantum absorbed or emitted by a body
is proportional to the frequency of radiation (f).
E photon = hf
The constant (h), which has a value of 6.63 x 10 J● s, is called Planck’s constant. Energy and
frequency are directly proportional to one another. This means that as one increases, the other also
increases such that the ratio of the two is equal to the constant h.
-34
C.6.C
Calculate the
wavelength,
frequency, and
energy using
Planck’s
constant and
the speed of
light.
Calculating Wavelength, Frequency, and Energy of Light
How can you calculate the wavelength of light using its frequency and the speed
of light?
c = λf
Because the product of wavelength and frequency is equal to a constant, you can always calculate one of
these variables if you know the value of the other. For example, if you know the frequency of a wave, you
can calculate its wavelength by dividing both sides of the equation by frequency. The result is:
λ= c
f
EXAMPLE #1:
14
14
Visible light has frequencies between 4.0 x 10 hertz (Hz) and 7.9 x 10 Hz. What are the wavelengths
of the lowest frequencies of visible light?
SOLUTION #1:
λ = 3.00 x 108 m/s = 0.75 x 10-6 m or 7.5 x 10-7 m
4.0 x 1014 Hz
How can you calculate the frequency of light using its wavelength and the
speed of light?
c = λf
If you know the wavelength of a wave, you can calculate its frequency by dividing both sides of the
speed of light equation by wavelength. The result is:
f=
c
λ
EXAMPLE #2:
-7
If a particular green light has a wavelength of 4.9 x 10 m, what is its frequency?
SOLUTION #2:
f = 3.00 x 108 m/s = 0.61 x 1015 s-1 or 6.1 x 1014 s-1
4.9 x 10-7 m
How can you calculate the energy of light from its frequency using Planck’s
constant?
E photon = hf
The constant h is known as Planck’s constant. Planck’s constant is equal to 6.63 x 10 J● s, read joule-1
seconds. To determine the units of energy, multiply the unit for h, J● s, by the unit for f, s , to obtain J,
the quantity of joules.
-34
EXAMPLE #3:
14
-1
The human eye can see light with a frequency about as high as 7.9 x 10 Hz or s , which appears violet.
Calculate the energy that one photon of violet light carries.
SOLUTION #3:
E photon = hf
E = (6.63 x 10-34 J● s) (7.9 x 1014 s-1) = 52.3 x 10-20 J or 5.2 x 10-19 J of energy.
How can you calculate the energy of light from its wavelength using Planck’s
constant and the speed of light?
E photon
=
hc
λ
EXAMPLE #4:
Find the energy of violet light if λ
= 4.0 x 10-7 m
SOLUTION #4:
E photon = (6.63 x 10-34 J● s)(3.00 x 108 m/s) = 5.0 x 10-19 J
4.0 x 10-7 m
C.6.D
Use isotopic
composition to
calculate
average atomic
mass of an
element.
Carbon Isotopes
Number of
protons
Number of
neutrons
Mass number
Carbon-11
6
Carbon-12
6
Carbon-13
6
Carbon-14
6
5
6
7
8
11
12
13
14
Calculating Average Atomic Mass
What is an isotope?
Atoms of the same element, so same # of protons, with different numbers of neutrons are called
isotopes.
The mass number of an atom is the sum of the atom’s protons and neutrons. The mass number is
used to identify an isotope and is written after the element name. For example, carbon-14 identifies an
isotope of carbon with 6 protons and 8 neutrons. The different isotopes of carbon are shown below.
Examples of carbon isotopes:
How is isotopic compositions used to calculate average atomic mass
of an element?
Each element has several isotopes. Rather than listing the mass numbers for all isotopes, the periodic
table lists the average atomic mass of each element. The atomic mass of an element is an average
mass that is weighted based on the abundance of the isotopes, or isotopic composition, of the
element.
To calculate the average atomic mass of elements you will need to know the abundance of the
isotopes for that particular element.
Let’s use the isotopic composition of chlorine to calculate the average atomic mass for chlorine.
See chart that follows:
Isotopic Composition of Chlorine
Isotope
Atomic mass (amu)
Chlorine-35
Chlorine-37
34.969
36.966
Approximate abundance
(percent)
75.78 %
24.22 %
Problem:
Calculate the average atomic mass using the data shown above. To calculate the average atomic mass
of elements, multiply the atomic mass (in amu) of each isotope given by its percentage abundance in
decimal form. Then add the products together.
So, to calculate the average atomic mass of chlorine you will have to do the following: See chart
above.
(34.969 amu) (0.7578) + (36.966 amu) (0.2422)
= 26.50 amu + 8.953 amu
= 35.45 amu
The average atomic mass of chlorine is 35.45 amu.
C.6.E
Express the
arrangement of
electrons in
atoms through
electron
configurations
and Lewis
valence electron
dot structures.
Electron Configurations and Lewis Valence Electron Dot Structures
How do quantum numbers describe atomic orbitals?
The modern atomic theory states that the locations of electrons aren’t exact. Instead, mathematical
expressions called atomic orbitals describe the probability of finding an electron at various locations
around the nucleus. Atomic orbitals differ by size, shape, and energy.
The energy levels of electrons are labeled by principal quantum numbers (n). These numbers have
positive integer values of 1, 2, 3, and so on. Electrons with the same principal quantum number are in the
same principal energy level. Each level contains one or more sublevels. Each sublevel contains one or
more atomic orbitals.
The second quantum number describes the shape of the atomic orbitals in a sublevel. Each shape is
denoted by a letter. The number of subleves is equal to the principal energy level number. For example,
level n = 1 has one sublevel, the s sublevel. Level n = 2 contains two sublevels---the s and p sublevels.
Level n = 3 has three sublevels---s, p, and d.
The third quantum number describes the orientation of the orbital in space. It also describes the
number of orbitals in a particular sublevel. The s sublevels contain one orbital, p sublevels contain
three orbitals, d sublevels contain five orbitals, and f sublevels contain seven orbitals.
Maximum of 2 electrons can go one each orbital.
Sublevel
s
Number of Orbitals
1
Maximum number
of Electrons
2
p
d
f
3
5
7
6
10
14
Each orbital can contain 0, 1, or 2 electrons; each with opposite spin direction. This is called the Pauli
exclusion principle.
Atomic Orbitals and Electrons in Principal Energy Levels
Principal energy
level
1
2
3
4
Type of sublevel
Number of orbitals in
sublevels
s
s, p
s, p, d
s, p, d, f
1
1+3=4
1+3+5=9
1 + 3 + 5 + 7 = 16
Maximum number of
electrons
2
8
18
32
How is the arrangement of electrons expressed by electron configurations?
An electron configuration describes which atomic orbitals hold the atom’s electrons. The arrangement
of any atom’s electrons can be determined by filling lowest energy orbitals first. One exception to
pattern is 4s orbitals are lower energy than 3d orbitals.
Element
N
Ne
Mg
Br
Electrons
Configuration
2
7
10
12
35
2
3
1s 2s 2p
2
2
6
1s 2s 2p
2
2
6
2
1s 2s 2p 3s
2
2
6
2
6
2
10
5
1s 2s 2p 3s 3p 4s 3d 4p
Alternate Format
------2
[Ne]3s
2
10
5
[Ar]4s 3d 4p
How is the arrangement of valence electrons expressed by Lewis valence electron
dot structures?
Lewis valence dot structure: Uses dots to represent atom’s valence electrons (highest energy
electrons in outermost energy level). The first four dots are arranged individually on four sides of the
symbol. Each additional dot is paired with one of the first four dots.
1
C.12.A
Describe the
characteristics
of alpha, beta,
and gamma
radiation.
Types of Radiation
Unlike normal reactions, nuclear reactions affect the nucleus. They can convert one element to another,
releasing particles and tremendous energy. Three main types of nuclear radiation are alpha radiation,
beta radiation, and gamma radiation.
Particle or Ray
Alpha (helium
nucleus)
Beta (electron
from nucleus)
Gamma ray
(photon)
Symbols
α=
β=
= no electrical
charge and no
mass
Charge
Mass
Speed
Penetration
+2
Large
Slow
Low
-1
Small
Fast
Low/medium
0
None
Fastest
Very high
What are the characteristics of alpha radiation?
An alpha particle is a helium nucleus emitted by a radioactive source. Another name for alpha particles
is alpha radiation. The radioactive decay that results in alpha radiation is often called alpha decay. Each
alpha particle consists of two protons and two neutrons and has a double positive charge.
When the nucleus emits alpha radiation, the mass number decreases by 2 thereby changing the
identity of the element. For example:
The above nuclear equation shows alpha decay in a uranium isotope with atomic # = 92 and mass # is
238.
•
•
•
When the nucleus emits alpha radiation, its atomic number decreases by 2, so the mass number
becomes 90. Because the atomic number has changed, the remaining nucleus is no longer a
uranium nucleus, but a thorium nucleus.
The mass number decreases by 4, so the mass number is becomes 234.
Since the number of protons has decreased, the overall charge of the nucleus has decreased by
2.
What are the characteristics of beta radiation?
An electron resulting from the changing of a neutron into a proton is called a beta particle. The neutron
breaks apart a proton, which remains in the nucleus, and a fast-moving electron, which is released.
neutron
proton
electron (beta particle)
Example 1
Example 2
The above nuclear equations show beta decay in thorium (example 1) and carbon (example 2).
•
•
The mass number does not change.
The number of protons increases by 1. Thus, the atomic number increases by 1 and the atom’s
identity changes. In example 1, Thorium becomes Protactinium. In example 2, Carbon becomes
Nitrogen.
A related radioactive decay process that is sometimes classified as beta plus radiation is positron
emission. In this process, a proton in an unstable nucleus changes to a neutron and releases a positively
charged electron. A positron is represented by the notation :
Example 1
Example 2
What are the characteristics of gamma radiation?
A third type of radioactive decay is called gamma radiation. A high-energy photon emitted by a
radioisotope is called a gamma ray. The high-energy photons are a form of electromagnetic radiation.
Nuclei often emit gamma rays along with alpha or beta particles. Gamma radiation differs from other types
of electromagnetic radiation, such as visible light and radio waves, because it has much higher energy
and because it is emitted by the nucleus. The symbol for a gamma ray is the Greek letter gamma, γ.
C.12.B
Describe
radioactive
decay process
in terms of
balanced
nuclear
equations.
Balanced Nuclear Equations
Balanced nuclear equations can be used to describe radioactive decay. Nuclear reactions use a
superscript on each term to show atomic mass and subscripts to show atomic number (protons);
totals before and after reaction must equal (proton changes to neutron to make β).
Example 1 : Alpha Decay-Why is this an example of alpha decay? Explain why Th is the new
element formed?
238
234
U
92
→
4
Th +
90
He
2
Example 2: Beta Decay-Why is this an beta decay? Explain why N is the new element formed.
14
14
C
→
6
0
N
+
7
e
-1
Positron Emission-How is this equation different from the one above?
11
11
C
6
→
0
B
5
+
e
1
Example 3: Gamma Decay-
Gamma rays usually are emitted along with other particles. They do not usually appear in nuclear
equations since they do not affect the numbers.
TRY THESE:
Write a balanced nuclear equation for the beta decay of bismuth-210.
C.12.C
Compare
fission and
fusion
reactions.
FISSION AND FUSION REACTIONS
What is a fission reaction?
When the nuclei of certain isotopes are bombarded with neutrons, they undergo fission, the breaking
apart of a nucleus into smaller fragments (pieces). Fission can occur if an atom’s nucleus is unstable.
3 neutrons also produced
This is a simple diagram illustrating an example of nuclear fission. A U-235 nucleus captures and
absorbs a neutron, turning the nucleus into a U-236 atom. The U-236 atom experiences fission into
Ba-141, Kr-92, three neutrons, and energy.
The ejection of neutrons as a result of the fission reaction is important. These neutrons can, in turn, strike
more nuclei, causing them to undergo fission. The result is a chain reaction. Chain reactions release a
tremendous amount of energy in a very short time. Fission must be controlled when it is used for the
production of electricity and nuclear power plants. Why?
Only 2 neutrons emitted in the above equation. What elements were formed?
What is a fusion reaction?
Fusion is a nuclear process in which two light nuclei combine to form a single heavier nucleus. An
example of a fusion reaction important in thermonuclear weapons and in future nuclear reactors is the
reaction between two different hydrogen isotopes to form an isotope of helium :
H + 3H ----> 4He + n
2
Fusion can release much more energy than fission, but fusion is not used for the production of electricity
at power plants. An enormous amount of energy is required to start the reaction.
Distinguishing between Fission and Fusion
Both fission and fusion release enormous amounts of energy. Both fission and fusion reactions can occur
in nuclear bombs. So, how can you tell fission and fusion apart?
FISSION
Heavy nucleus breaks into lighter nuclei
Can emit neutrons that can cause other
fission reactions
Releases enormous amount of energy
• Radioactive byproducts
• Uses uranium, a nonrenewable
resource
FUSION
Light nuclei combine to form a heavier
nucleus (sun)
Products do not result in a chain reaction
Releases more energy than fission
• No radioactive by products
• Uses easily available hydrogen
isotopes
• Much higher energy needed to
initiate fusion than fission
• Extreme temperatures required make
it unusable for production of
electricity