Notes Ch. 4 and 25: Atomic Structure and Nuclear Chemistry
History and Structure of the Nuclear Atom
The Atom
• smallest particle of an element that retains all properties of the element
Early Models of the Atom
A. Democritus (460 B.C. – 370 B.C)
• first to suggest the existence of ____________
• believed atoms were indivisible and indestructible
B. Dalton
• Atoms of the same element are ____________
• Each element is unique
• Atoms combine in fixed ratios to form compounds
C. Thomson
• Discovered ____________
• Suggested atom looked like plum pudding (or a blueberry muffin or chocolate chip cookie) with
electrons evenly distributed throughout positive sphere
D. Rutherford
• Conducted gold foil experiment
• Proposed atom is mostly empty space
• Concluded all positive charge and mass is concentrated in small region called ____________
E. Bohr
• depicts the atom as a small, positively charged nucleus
• surrounded by electrons that travel in circular ____________around the nucleus
F. Schrödinger
• model allowed the electron to occupy three-dimensional space like an electron “____________”
• Used a mathematical equation to show a model of electrons as waves
II. More about the Atom
A. Size
• Teeny tiny
• observable with instruments such as a scanning tunneling ____________
I.
B. Parts (called Subatomic Particles)
1. Protons: p+
• charge =
positive +1
• mass = 1
2. Electrons: e• charge =
negative -1
• mass ~ 0
C. Location of Parts
• Nucleus: center of atom
- contains protons and neutrons
- has a positive charge
- contains almost ALL of the __________of the atom
• Outside nucleus:
- contains ____________
- has a negative charge
- occupies almost ALL of the volume of the atom
D. Atomic Charge
• ____________are NEUTRAL
• # of protons = # of electrons
(ALWAYS if you’re talking about an ATOM)
1
3.
Neutrons: no
• charge = zero
• mass = 1
How Atoms Differ
I.
Properties of Subatomic Particles
Particle
Symbol
Electron
e- or
0
e
Location
Relative
Charge
-1
Relative
mass
Actual mass (g)
-28
1-
9.11 x 10
1+
1.673 x 10
0
1.675 x 10
p+ or
Proton
1
1
Neutron
1
0
or
In the nucleus
-24
-24
II. Atomic Number
• the number of ________________ in an atom
• Identifies element
– each atom has unique #
– # never changes
III. Mass number
• represents the _____________________ of the number
of _____________________ and neutrons in the nucleus
• # of neutrons = mass number – atomic number
IV. Isotopes
• Atoms of the same element but have a different # of neutrons
• Ex: 3 isotopes of carbon: Carbon-12,
Carbon-13,
Carbon-14
____# protons, ____# protons, ____ # protons
____# neutrons, ____# neutrons, ____ # neutrons
• All elements have isotopes (some 2, some 3, etc.)
• Some isotopes are naturally radioactive.
• Ex: Plutonium
V. Representing Isotopes
• In Ag-107, the 107 represents the mass number (neutrons + protons)
• the 47 represents the number of protons)
Practice:
1. What is the mass number for Co-59?
2. What is the mass number for 73Li?
VI. Atomic Mass
• The standard is the atomic mass unit (amu): defined as 1/12 of the mass of a carbon-12 atom
• the weighted average of the isotopes of that element.
• Formula:
Atomic
% abundance
mass
% abundance
mass
mass of
of
of
of
of
= (
x
) + (
x
) +
…
an element
Isotope #1
Isotope #1
Isotope #2
Isotope #2
Practice 3
• Silver has two naturally occurring isotopes. Ag-107 has an abundance of 51.82% and mass of 106.9 amu. Ag-109 has
a relative abundance of 48.18% and a mass of 108.9 amu. Calculate the atomic mass of silver.
2
Practice 4
87
85
•
Rubidium is a soft, silvery-white metal that has two common isotopes, 85
37Rb and 37Rb. If the abundance of Rb is
87
72.2% and the abundance of Rb is 27.8%, what is the average atomic mass of rubidium?
Vocabulary to Know
• Atomic #- same # of protons & electrons
• Mass #-protons + neutrons
14
written 2 ways: Carbon-14 or 6 C
• Isotopes-same # of protons, different # of neutrons
• Atomic mass-weighted average mass
Types of Radiation and Unstable Nuclei
I. Chemical and Nuclear Reactions
• Chemical reactions only involve an atom’s _________________________
• ____________________ reactions involve changing an atom’s nucleus
• Nuclear reactions release about a ______________________ times more energy than chemical reactions
• Unlike chemical reaction, nuclear reactions are not affected by ________________________, pressure, or a catalyst.
II. Nuclear Vocabulary
• Radioactivity – the process of emitting _________________________
• Radiation - _______________ and particles emitted by a radioactive source.
• Radioisotopes – _____________________ of atoms with unstable nuclei and emit radiation to obtain a more stable
nuclei
• Radioactive decay -____________________nuclei losing energy by emitting radiation in a spontaneous process.
• Nucleon – refers to both ________________________ and neutrons
III. Which Isotopes are Radioactive?
• Small Nuclei - Atoms which contain up to _______ protons (up to Calcium) are usually ____________________.
• Large Nuclei - Larger nuclei tend to be _______________________. All nuclei with _______ or more protons
(Polonium and up) are radioactive. For example, all isotopes of Uranium are radioactive.
• Atoms with more neutrons than protons - There are radioactive nuclei that have less than 84 protons. These nuclei
have more neutrons than protons. For example, Carbon-12 (6 protons and 6 neutrons) is stable, while
_________________________ (6 protons and 8 neutrons) is radioactive.
IV. Why Does an Atom Undergo Radioactive Decay?
• Radioactive atoms emit radiation because their nuclei are
_________________________.
• The stability of the nucleus depends on the ______________________ to
___________________ ratio
• Neutrons vs. protons graph stable nuclei found in a region called the band of
__________________________.
V. Types of Radiation – Alpha Radiation
• Alpha radiation are attracted to the negatively charged plate
• Alpha particles contain two protons and two neutrons (A
__________________ nucleus)
3
•
•
•
•
Blocked by_______________________
Least penetrating form of radiation (only travels a few centimeter in the air)
Carry +2 charge
4
Symbolized by 2 ______ or 42 
VI. Types of Radiation – Beta Radiation
• Beta radiation attracted to the positively charged plate
• Carry –1 charge
• Beta particles are fast moving ________________________
• Blocked by metal foil or _______________________
• Medium penetration power (travels a few meters in the air)
0
• Symbolized by
_____ or -10 
-1
VII. Types of Radiation – Gamma rays
• Gamma rays are high energy radiation that possesses no ________________.
• Possess no electrical charge and are not deflected by magnetic or electrical fields.
• Not completely blocked by lead or _______________________
• The most penetrating and damaging type of radiation
• Carry no charge
• Symbolized by 00 ______________
VIII. Electron Capture
• Electron capture occurs when a nucleus of an atom draws in an ______________________.
0 e → 81 Kr
• 81 Rb +
-1
37
•
36
Also known as __________ capture
IX. Electrostatic Force
• Electrostatic force is when like charges ______________ and opposite charges __________________.
X. Strong Nuclear Force
• that are extremely ______________________ together. It keeps the nucleus ____________________.
Remember Mass Number and Atomic Number 
XI. Writing and Balancing Nuclear Equations
• In a balanced nuclear equation, mass numbers and atomic numbers are
_____________________________.
Example
230
226
4
90 Th  88 Ra + 2 He
– Notice the mass numbers and atomic numbers add up to the same on both sides of the equation
Practice
1. 97
Zr  -10 e
+ ?
40
2.
218
84 Po
3. ? 

4
2 He
222
86 Rn
-1
+
+ ?
4
2
4.
47
Ca
20

0
e
-1
5.
244
96 Cm

4
2 He
He
+ ?
+ ?
4
Transmutation
I.
Transmutation
• Transmutation - The conversion of one element to _____________________ element.
• All nuclear reactions are transmutation reactions except for __________________ emission, which does not alter an
atom’s atomic number.
II. Induced Transmutation
• Before 1919, the only way to change the nucleus or cause transmutation was to wait for
_______________________.
• In 1919 Rutherford was the first to induce (_____________________) transmutation.
• He proved that nuclear reactions can be produced __________________________.
• Induced transmutation can occur by ______________________an atom with alpha particles, protons or neutrons.
III. Transuranium Elements
• Elements with atomic number above __________.
• All transuranium elements undergo transmutation
• None of the transuranium elements occur in __________________ and have only been produced through induced
transmutation.
IV. Half-life
• The time required for _______________________ of a radioisotope’s nuclei to decay into its products
• After each half-life, half of the existing radioactive atoms have decayed into atoms of a _____________ element
• Amount remaining at time T = (initial amount)(1/2)n
where n= number of half-lives
• n = total time ÷ time of one half-life
Practice
1. Scientists start with 50.0 g sample of a radioisotope. How much is left after four
half-lives?
2. Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron 59 is 44.5 days. How much
of a 2.000 mg sample will remain after 133.5 days?
V. Carbon-14 Dating
• Carbon 14 dating is the process of determining the _____________ of artifacts that were once part of a living
organism by measuring the amount of 14C _____________________ in that artifact
• Carbon-14 is radioactive and undergoes beta decay. It has a half-life of 5730 years.
Carbon-14
• 14C evenly spread in the Earth’s biosphere
• Plants incorporate 14C into their structure that matches the level in the atmosphere.
• When an organism dies, 14C declines at a known rate. (Half-life of C-14 = 5730 years)
• Comparing the remaining 14C fraction of a sample to that expected from atmospheric 14C allows the age of the
sample to be estimated.
• Dates carbon-bearing materials up to 62,000 years.
5
•
Carbon-14 Decay
•
Using the graph, about what % of carbon-14 remains after 11, 400 years?
Fission and Fusion of Atomic Nuclei
I. Nuclear Fission
• Fission - The splitting of the nucleus into ______________________ (division)
• Uranium-235 is struck by a neutron and forms Ba-141, Kr-92, and additional neutrons.
II. Chain Reaction
• Chain reaction
– Nucleus captures a neutron and splits into fragments and produces three neutrons
– _____________________ start a new reaction
• Critical mass
– The ___________________ mass required to support a self-sustaining chain reaction
III. Nuclear Fusion
• Fusion - ____________________ atomic nuclei to produce a nucleus of greater __________________
• Fusion reactions release _______________ energy than fission reactions
• The ________________ is powered by fusion
IV. Nuclear Binding Energy
• The energy required to break a nucleus into its individual protons and neutrons
• Energy released in a nuclear reaction is much ____________________ than in
chemical reactions
V. Mass Defect
• When breaking apart a nucleus, there is a change in mass called the mass defect.
• The change in mass was converted to energy.
• We know this as E=mc2
VI. Nuclear Reactors
• The purpose of nuclear reactors is to keep the chain reaction going without letting it get out of control
VII. Nuclear Bombs
Atomic Bomb
• Uses_________________________
• Uses enriched uranium-235 or plutonium
• Nagasaki and Hiroshima
Hydrogen Bomb
• Uses _________________________
• 1000 time more powerful than atomic bomb
• Uses deuterium 2H and tritium 3H
6