Download Atomic Number - Physical Science

Atomic Structure
and Nuclear
Radiation
CHAPTER 19.1, 25
Structure of the Atom
CHAPTER 19, SECTION 1
Chemical Symbols
• Chemical symbol: a letter or combination of letters to
represent an element
• First letter is always capitalized
• For some elements, the symbol is the first letter of the
element’s name
• Some symbols are derived from Latin
• Ex: the symbol for silver, Ag, comes from the Latin word
argentum
Chemical Symbols
Atomic Components
• Atom: the smallest piece of matter that retains the
property of an element
• Atoms are made up of subatomic particles:
• Protons: subatomic particles with a charge of +1
• Electrons: subatomic particles with a charge of -1
• Neutrons: subatomic particles with no charge
• Atoms of different elements have a different
number of protons
Location of Subatomic Particles
electrons
protons
nucleus
neutrons
6
Quarks
• Protons and neutrons are made up of smaller
particles called quarks
• Scientists have found evidence that supports
the existence of 6 quarks
• They theorize that a certain arrangement of 3 quarks
produce a proton
• Other arrangements of 3 quarks produce neutrons
Atomic Mass
• The nucleus contains most of the mass of an atom
because protons and neutrons are far more massive
than electrons
• The mass of the proton and neutron are the same
• Proton: 1.6726 X 10-24
• Neutron:1.6726 X 10-24
• Electron: 9.1093 X 10-28
Protons Identify an Element
• Atoms of different elements are different because they
have different numbers of protons
• The protons tells you what type of atom you have
• The number of protons in an atom is equal to a number
called the atomic number
• Atomic number of Carbon is 6
• So carbon has 6 protons
Mass Number
• The mass number of an atom is the sum of the number
of protons and the number of neutrons in the nucleus of
a tom
• Atomic Mass = Number of neutrons + Atomic Number (Number
of Protons)
• Number of neutrons = Mass number – atomic number
How to write this…
Example
Mass Number
23
11
Atomic Number
Element Symbol
Na
Another Way to Write Elements…
Mass Number
23
11
Na
Mass Number
Sodium – 23
or
Na - 23
Practice!
• How many protons, electrons, and neutrons are in each
atom?
1. 94Be
2. 147N
3. 6530Zn
4. 8035Br
Bell Work 2/25/16
1. What are the rules for writing a Chemical Symbol for an element? (you
should have two of these)
2. How do you find the number of neutrons present in an atom?
3. Complete the following table
Particle
Proton
Neutron
Electron
Location in Atom
Charge
Mass
Let make sure we got this before we move on
Substance
Sodium
Silver
Zinc
Chlorine
Chemical
Symbol
Atomic
Number (Z)
Atomic Mass # of Protons
(A)
# of Neutrons # of
Electrons
Atomic Mass & Number
CHAPTER 19, SECTION 2
Atomic Mass
• The unit of measurement for atomic particles is the
atomic mass unit (amu)
• The mass of a proton is about the same as that of a
neutron (~1 amu)
• Atomic mass unit (amu): one-twelfth the mass of a
carbon atom containing six protons and six neutrons
Atomic Number
• The number of protons tells you what type of atom you
have
• Atomic number: the number of protons in an atom
• The atomic number is different for each of the elements
• Ex: State the number of protons for atoms of each of the
following:
• Nitrogen (N)
• Sulfur (S)
• Barium (Ba)
Atomic Number
• If an atom is neutral (it has NO charge), then there
must be the same number of electrons as protons
in that atom
Neutral atom:
# of protons = # of electrons
Mass Number
• Mass number: the sum of the protons and
neutrons in the nucleus of an atom
Mass Number = # protons + # neutrons
• So, if you want to find # neutrons…
# of neutrons = mass # - atomic #
How to write this…
Example
Mass Number
23
11
Atomic Number
Element Symbol
Na
Another Way to Write Elements…
Mass Number
23
11
Na
Mass Number
Sodium – 23
or
Na - 23
Practice!
• How many protons, electrons, and neutrons are in each
atom?
1. 94Be
2. 147N
3. 6530Zn
4. 8035Br
Isotopes
• Isotopes:
• Atoms with the same number of protons, but different
numbers of neutrons
• Atoms of the same element (same atomic number) with
different mass numbers
Isotopes of chlorine:
35 Cl
17
37 Cl
17
chlorine – 35
chlorine - 37
Isotopes
Isotopes of carbon include: carbon-12, carbon-13,
and carbon-14
Write the symbol for each isotope using superscripts
and subscripts to represent the mass and atomic
numbers
Learning Check
Write the atomic symbols for atoms with the following:
A. 8 p+, 8 n0, 8 e-
___________
B.
17p+, 19n0, 17e-
___________
C. 47p+, 60 n0, 47 e-
___________
Ions
• Ion: an atom that has gained or lost
electrons
• In non-nuclear chemistry, an atom never
gains or loses a proton; only the number of
electrons is affected during chemical
reactions
Ions
• To determine the charge of an ion,
compare the # of protons and # of
electrons
• If there are more protons, the ion has a positive
charge equal to the extra protons
• If there are more electrons, the ion has a
negative charge equal to the extra electrons
Cations
• Cations 
• Positive charge
• Formed by losing electrons
• Metals form cations
Ca  Ca2+ + 2e-
Anions
• Anions 
• Negative charge
• Formed by gaining electrons
• Non-metals form anions
O + 2e-  O2-
Writing Chemical Symbols for Ions
• Oxygen (O) has 8 protons, 8 neutrons, but has a
tendency to gain two electrons.
• This is written as follows:
16 O28
• Write the chemical symbol for the ion with 13
protons and 10 electrons.
27 Al3+
13
Average Atomic Mass
• Average atomic mass: the weighted-average
mass of all the atomic masses of the isotopes of
that atom
• Ex: Four of five atoms of boron are boron-11 and
one out of five atoms of boron are boron-10
4/5 (11 amu) + 1/5 (10 amu) = 10.8 amu
*Note that the average atomic mass of boron is closer to
boron-11 as it is more abundant in nature
Homework Quiz
• Part I
• Complete the Chart
• Part II
• #1-10 on the backside (Matching)
Complete the Following Table
Atomic #
Mass #
# p+
# e-
1) 17
2)
180
3)
4) 92
5)
40
238
# n0
charge
19
0
71
109
38
46
Symbol
86
206
82
Pb4+
Complete the Following Table
Atomic # Mass #
# p+
# e-
1) 14
2)
16
75
3)
4) 99
5)
# n0
51
252
36
42
54
79
charge
Symbol
+4
96
208
82
Pb2+
Bell Work 2/29
• Please write the following questions and answers in
your composition notebooks
1. What is an ion?
2. What is an Isotope?
3. What is the number of neutrons that Carbon-14 has?
4. How many electrons does Ni+2 have
Radioactivity
C H AP TER 2 5 , SE C T I ON 1
Elements and Protons
• Recall that every element has a different number of
protons
• For an atom of one element to change into a different
element, the number of protons in its nucleus must
change
• The nucleus of an atom contains almost all the mass,
but it occupies only a tiny fraction of space in the
atom
• The size of a nucleus in an atom can be compared to a
marble sitting in the middle of an empty football stadium
The Strong Force
• Within the nucleus, the positive electric forces of the
protons repel each other
• So why don’t the protons push each other away?
• The strong force causes protons and neutrons to be
attracted to one another
• This force is 100 times stronger than electric force
• In order for the strong force to be effective, the particles must
be close to one another
The Strong Force
• The fewer protons and neutrons in a nucleus of an
atom, the stronger the strong force that holds
them together
• The more protons and neutrons in a nucleus of an
atom, the weaker the strong force that holds them
together
Radioactivity
• Many nuclei are held together permanently and are
stable
• Some types of nuclei are unstable
• These nuclei break apart, or decay, by emitting particles
and energy
• Radioactivity: the ability of an atom to emit, or give
off, charged particles and energy from its nucleus
Radioactivity
• Nuclei that contain a large number of protons
and neutrons tend to be unstable
• All nuclei that contain more than 83 protons are
radioactive
• Almost all elements with more than 92 protons
don’t exist naturally on Earth
Converting Mass into Energy
• According to the law of the conservation of mass,
mass cannot be created or destroyed
• However, in nuclear reactions, mass can be
converted into energy
• A large amount of energy is produced by the conversion
of only a small amount of mass
Isotopes & Nuclear Numbers
• Isotopes of the same element contain the same
number of protons, but a different number of neutrons
• The total number of protons and neutrons in an atom is
called the mass number
• When writing the symbol for an atom, use the AZX format
• You can also indicate the mass of an isotope by writing
it after the name of the element
• Ex: carbon-14 has a mass of 14 amu
Nuclear Decay
C H AP TER 2 5 , SE C T I ON 2
Nuclear Radiation
• There are three types of nuclear radiation:
• Alpha
• Beta
• Gamma
• Alpha and beta radiation are particles, while
gamma radiation is an electromagnetic wave
Alpha Particles
• Alpha particle: a particle made of two
protons and two neutrons that is emitted from
a decaying nucleus
• An alpha particle is the same as the nucleus
of a helium atom and has the symbol:
4 He
2
• Alpha particles have the most mass and
electric charge of all types of nuclear
radiation
Alpha Particles
• Alpha particles exert an electric force on
electrons in atoms along their path, leaving
charged ions behind
• Alpha particles lose energy quickly
• Alpha particles are the least likely to travel
through matter and can be stopped by a sheet of
paper
Alpha Particles
• Alpha particles can be dangerous if they are
released by radioactive atoms inside the human
body
• Damage from alpha particles can cause cells not
to function properly, leading to illness and disease
• Some smoke detectors give off alpha particles to
ionize the surrounding air
• If smoke particles enter the ionized air, they will absorb
the ions and electrons so the circuit is broken and the
alarm goes off
Alpha Particles
• Transmutation: the process of changing one
element to another through nuclear decay
• In alpha decay, two protons and two neutrons are
lost from the nucleus
• Thus, alpha decay forms a new element that has
an atomic number two less than that of the
original element
• In addition, the mass number of the new element
is four less than the original element
Alpha Particles
Beta Particles
• Beta particle: the electron emitted from an unstable
nucleus when a neutron decays into a proton
• Beta particles are symbolized like this:
0 e
-1
or
0 β
-1
• Beta decay is caused by another basic force called
the weak force
• The new atom formed in beta decay has one more
proton, but the mass of the atom is unchanged from
the original element
Beta Particles
Beta Particles
• Beta particles are much faster and can travel
through matter much better than alpha particles
• They can pass through paper, but are stopped by a
sheet of aluminum foil
• Beta particles can damage cells when they are
emitted by radioactive nuclei inside the human
body
Beta Particles
Beta Particles
• Positron emission: a subtype of beta decay in
which a proton inside a radioactive nucleus is
converted to a neutron while releasing a positron
(positively charged particle)
• Symbolized as follows:
0 β
+1
Gamma Rays
• Gamma rays: electromagnetic waves with the highest
frequencies and the shortest wavelengths in the
electromagnetic spectrum
• Gamma rays have no mass and no charge and travel
at the speed of light
• Gamma rays are symbolized as follows:
0 γ
0
• Gamma rays are usually emitted from a nucleus when
alpha decay or beta decay occurs
Gamma Rays
Gamma Rays
• Gamma rays can be
stopped by blocks of dense
materials, such as lead and
concrete
• However, gamma rays cause
less damage to biological
molecules as they pass
through living tissue because
it has no mass or electric
charge
Radioactive Half-Life
• Half-life: a measure of the time required by the
nuclei of an isotope to decay
• The nucleus left after the isotope decays is called
the daughter nucleus
• Half-lives vary widely among radioactive isotopes
• Ex: Polonium-214 has a half-life of less than a thousandth
of a second
• Ex: Uranium-238 has a half-life of 4.5 billion years
Calculating Half-Life
• There are two ways to calculate half-life:
1. Use the formula:
t1/2 = (t x log2) / log (N0/Nt)
2. Manually calculate the half-lives of the
substance until the desired amount is reached
Half-Life Example
• Suppose the initial number of atoms of a
radioactive isotope is 2016 and after 35 days it
decays to 63. Calculate the half-life of the
substance.
Initial amount = 2016
Final amount = 63
Time = 35 days
• Simply divide the initial amount by 2 until it is
reduced to 63
Half-Life Example
• First half-life: 2016/2 = 1008
• Second half-life: 1008/2 = 504
• Third half-life: 504/2 = 252
• Fourth half-life: 252/2 = 126
• Fifth half-life: 126/2 = 63
• Therefore, it takes 5 half-lives to undergo decay from 2016 to 63
atoms. In other words, it takes 35 days to complete 5 half-lives.
• The half-life of the isotope is therefore, 35 days / 5 half-lives = 7 days
Carbon Dating
• The radioactive isotope carbon-14 is often used to
estimate the ages of plant and animal remains
• Carbon-14 has a half-life of 5,730 years and is
found in molecules such as carbon dioxide
• The decaying carbon-14 in a plant or animal is
replaced when an animal eats or when a plant
makes food
• As a result, the number of carbon-14 atoms
compared to the number of carbon-12 atoms
remains nearly constant
Carbon Dating
• But when an organism dies, its carbon-14 atoms
decay without being replaced
• The carbon-14 to carbon-12 ratio decreases with
time allowing the age of the organism’s remains
to be estimated
• However, only material from plants and animals
that lived within the past 50,000 years contains
enough carbon-14 to be measured
Uranium Dating
• Radioactive dating also can estimate the ages of
rocks
• Some rocks contain uranium, which has two
radioactive isotopes with long half-lives
• Each uranium isotope decays into a different
isotope of lead
• From the ratios of the uranium isotopes to their
daughter nuclei, the number of half-lives since the
rock was formed can be calculated
•What is the half-life of a 100.0 g
sample of nitrogen-16 that decays
to 12.5 grams in 21.6 seconds?
•A 208 g sample of sodium-24
decays to 13.0 g of sodium-24
within 60.0 hours. What is the
half-life of this radioactive
isotope?
Nuclear Reactions
C H AP TER 2 5 , SE C T I ON 4
Nuclear Fission
• Nuclear fission: the process of splitting a nucleus into
several smaller nuclei
• Only large nuclei, such as uranium and plutonium
undergo nuclear fission
• A fission reaction usually produces several individual
neutrons in addition to the smaller nuclei
Nuclear Fission
• The total mass of the products is slightly less than
the mass of the original nucleus and the neutron
• This small amount of missing mass is converted to a
tremendous amount of energy during nuclear
fission
Nuclear Fission
Nuclear Fission
• Albert Einstein proposed that mass and energy
were related in his special theory of relativity:
E = mc2
• A small amount of mass can be converted into an
enormous amount of energy
• Ex: if 1 g of mass is converted to energy, about
100 trillion joules of energy are released
Nuclear Fission
• When a nuclear reaction occurs, the neutrons
emitted can strike other nuclei in the sample and
cause them to split
• These reactions release more neutrons, causing
additional nuclei to split
• Chain reaction: the series of repeated fission
reactions caused by the release of neutrons in
each reaction
Nuclear Fission
• Chain reactions can be controlled by adding
materials that absorb neutrons
• In order for a chain reaction to occur, a critical mass
of material that can undergo fission must be present
• Critical mass: the amount of material required so that
each fission reaction produces approximately one
more fission reaction
• If less than the critical mass of material is present, a
chain reaction will not occur
Nuclear Fusion
• Nuclear fusion: two nuclei with small masses
combine to form a nucleus of larger mass
• Nuclear fusion reactions can release even more
energy than nuclear fission reactions
• Nuclear reactions release much more energy than
chemical reactions because the strong force is
much stronger than the electric force
Nuclear Fusion
• For nuclear fusion to occur, positively charged nuclei
must get close to each other
• If they are moving fast, their kinetic energy overcomes
the repulsive electrical force between them
• As the temperature increases, the kinetic energy of
atoms and molecules increases
• Only at temperatures of millions degrees Celsius are
nuclei moving so fast they can get close enough for
fusion to occur
• Ex: the Sun
Nuclear Fusion
• The Sun is made of mostly hydrogen
• Most of the energy given off by the Sun is
produced by the fusion of hydrogen nuclei
• The net result is that four hydrogen nuclei are
converted into one helium nucleus
Nuclear Fusion
Nuclear Fusion
• Earth receives a small amount of energy as
thermal energy and light
• As the Sun ages, the hydrogen nuclei are used up
as they are converted into helium
• It is estimated that the Sun has enough hydrogen
to keep reacting for another 5 billion years
The Periodic Table
C H AP TER 1 9 , SE C T I ON 3
Mendeleev’s Periodic Table
• In the 1800s,
Dmitri
Mendeleev
searched for a
way to organize
the elements
• He arranged
them in order of
increasing
atomic mass
Today’s Periodic Table
• Mendeleev found that certain chemical
properties were repeated in specific patterns
• However, masses of the elements do not follow a
strict pattern
• Today, we arrange the periodic table in order of
increasing atomic number
Modern Periodic Table
Groups & Valence Electrons
• Groups(aka families): the vertical columns that
are numbered 1 through 18
• Elements in the same group have similar properties
• According to the Electron Cloud Model, electrons
within a certain cloud have different amounts of
energy
Groups & Electrons
• Electrons are placed in
specific energy levels
according to the
amount of energy they
have
• Energy levels nearer the
nucleus have lower
energy than those
farther away
Groups & Electrons
• Electrons fill energy levels of lowest energy
first
• Elements in the same group have the same
number of electrons in their outer energy
levels (valence electrons)
• It is the number of valence electrons that
determine the chemical properties of an
element
Groups & Electrons
• For Groups 1 and 2, the number of valence
electrons is equal to the group number
• For Groups 13 (3A) through 18 (8A), the
number of valence electrons is equal to the
group number minus 10 … or equal to
groupA #
Periods & Energy Levels
• Periods: the horizontal rows on the periodic
table
• Energy levels are numbered 1-7 and correspond
to the horizontal rows or periods, on the periodic
table
Metals, Nonmetals, and Metalloids
• Metals: generally good conductors of heat and electric
current
• Most elements (80%)
• Nonmetals: poor conductors of heat and electric
current
• Upper right-hand corner of periodic table except for hydrogen
• Metalloids: (aka semiconductors) have similar
properties to both metals and nonmetals
• Border the stair-step line that separates metals from nonmetals
Classifying Elements further
• Elements can be classified
as metals, nonmetals, and
metalloids
• Elements are further
classified into five families
• The elements in a family
have the same number of
valence electrons
Group
Number
# of valence
electrons
Name of
Family
1
1
Alkali Metals
2
2
Alkaline-earth
Metals
3-12
Varied
Transition
Metals
17
7
Halogens
18
8 (except He)
Noble Gases
• Soft and shiny
• Reacts violently with water
• Alkali metals are often store in oil
to prevent them from reacting
with moisture in the air
• Alkali metals are very reactive
because they have just one
valence electron that can be
easily removed to forma a
positive ion
• Only found in nature as a
compound because of its
reactivity
Alkali Metals
Alkaline- Earth Metals
• In general, alkalineearth metals are harder,
denser, stronger, and
have higher melting
points than alkali metals
• Two Valence Electrons
• Less reactive than alkali
metals, but still react to
form ions with +2 charge
• Groups 3-12
• Much less reactive than alkali and
alkaline metals
• Some transition metals can form
as many as four differently
charged cations because of their
complex arrangement of
electrons
• Transition metals are harder, more
dense and have higher melting
points (except Mercury)
Transition Metals
Halogens
• Most reactive
non-metals
• 7 valence
electrons
Nobel Gases
• Unreactive because
its s and p orbitals are
filled
• Do not gain or lose
electrons
Bell Work 3/9
• Please write the questions and the answer for the following questions in your composition notebook
1.
What is the group number for the following elements?
•
•
•
•
2.
Sodium
Fluorine
Sulfur
Germanium
What is the period number for the following elements?
•
•
•
•
3.
Arsenic
Potassium
Chlorine
Bismuth
What is the family name of the following elements?
•
•
•
•
4.
Mercury
Cesium
Radon
Chlorine
How many valence electrons do the following elements have?
•
•
•
•
Calcium
Carbon
Fluorine
Argon
Bohr Diagrams
• Steps to drawing a Bohr Diagram:
1. Find your element on the periodic table
2. Determine the number of electrons (note: it will
be the same as your protons for a neutral atom)
• This is how many electrons you will draw
Bohr Diagrams
3. Find out which period your element is on
• Elements in the 1st period have one
energy level
• Elements in the 2nd period have two
energy levels
• And so on…
4. Draw a nucleus and indicate the number
of protons (p) and neutrons (n)
Bohr Diagrams
5. Add the electrons
• One at a time
• Start on the top
and go clockwise
• Fill the lowest
energy levels first
• Use the following
table to help
Electron Shell
# of Electrons
1
2
2
8
3
8
4
18
5
18
6
32
7
32
Bohr Diagrams
• Note: The electron shells are a “model” for locating
valence electrons
• In actuality, electrons are found in orbitals (clouds)
according to energy levels
• The third energy level can contain a maximum of 18
electrons because of an overlapping in orbitals
• The fourth energy level can contain a maximum of 32
electrons because of an overlapping in orbitals
• BUT… we will only deal with the first few periods
Examples
Electron Dot Diagrams
• Recall that elements in the same group have the
same number of electrons in their outer energy
levels (i.e. they have the same number of valence
electrons!)
• Electron dot diagram: uses the symbol of the
element and dots to represent valence electrons
• The electron configuration of an atom determines
how it reacts with other atoms
Electron Dot Diagrams
• Steps to drawing electron dot diagrams:
1. Find your element on the periodic table and
write its chemical symbol
2. Determine the number of valence electrons
(the number of electrons in the outermost
shell)
• Determine what group (column) your element is in
• This will tell you the number of valence electrons to
draw
Electron Dot Diagrams
3. Draw your valence electrons
• One at a time
• Starting on the right moving clockwise
• Only place one electron per “side” before
coupling up
• You may only have a maximum of 8 valence
electrons around the symbol
Examples
Complete a Electron Dot Models for the
following elements in the space on your
worksheet
1. Calcium
2. Potassium
3. Argon
4. Aluminum
5. Bromine
6. Carbon
7. Helium
8. Oxygen
9. Phosphorus
10. Hydrogen