Chapter 3Atomic Theory
Today’s Objectives
• Understand the basics of Dalton’s Atomic Theory, and how it relates to the study of chemistry; be aware of how it differs from the currently accepted modern Atomic Theory.
• Know the basic details of how each subatomic particle was discovered, and what information was determined about protons, neutrons, and electrons in these experiments
Early Theories
• 4 elements
Democritus(460 - 370 BC)
• Greek philosopher• Atomos –
indivisible particles
• Atoms are the smallest particle that retains the chemical identity
Jabir Ibn Haiyan (700? - 803 AD)
• Father of Chemistry
• Practiced Alchemy
• Discovered metals
Lavoisier(1743 - 1794)
• Law of Conservation of Matter
Joseph Louis Proust(1754-1826)
• Law of Constant Composition
Dalton(1766 - 1844)
• Atomic Theory
Atomic Theory
• Elements made of atoms• Atoms are identical of a given
type of element• Atoms neither created nor
destroyed• Compounds have fixed ratio of
atoms
Ben Franklin(1706-1790)
• Two types of charge positive (+) and negative (-)
Michael Faraday(1791-1867)
• Atoms are related to electricity
J.J. Thomson(1856 - 1940)
• Cathode Ray Tube (CRT) stream of electrons
• Plum Pudding Model
cathode ray tube
Robert Millikan(1838-1953)
• Determined charge & mass of electron
Becquerel(1852 - 1908)
• Uranium exposes film
Marie (1867-1934) & Pierre Curie (1859-1906)
• Discovered radioactivity elements
• Radioactive decay
Rutherford(1871 - 1937)
• Discovered radioactivity particles
• Discovered Nucleus
• Solar system model of atom
Discovery of particles
gold foil experiment
Niels Bohr (1885 – 1962)
• Electrons do not orbit like planets
• Described shells or energy levels
• Quantum theory
H.G.J. Moseley (1887 - 1915)
• Discovered protons (+) in the nucleus
• Rearranged periodic table
Sir James Chadwick (1891-1974)
• Discovered neutrons (0) in the nucleus
Today’s Objectives
• Review History of the atom– Dalton’s Theory– History and discovery of each subatomic particle
• Discovery Learning:– Know the name, location, charge, and relative mass of each of the
subatomic particles in an atom– Know that the atomic number is the number of protons in the
nucleus of an atom, and is unique to each element.– Understand that isotopes are atoms of the same element that differ
in the number of neutrons in the nucleus, and therefore differ in mass.
– Know the mass number is, and be able to use it to correctly designate isotopes using both hyphen notation and nuclear symbols.
Protons
• Make up the nucleus
• Charge +1.602 x 10 -19C
• Mass = 1.673 x 10 -24g
• Charge +1
• Mass = 1 amu
Neutrons
• Make up the nucleus
• Charge 0
• Mass = 1.675 x 10 -24g
• Mass = 1 amu
Quarks, Quarks, Quarks (1950s – present)
• 6 quarks have been discovered that make up protons and neutrons
Electrons
• Occur in electron Clouds
• Charge -1.602 x 10 -19C• Mass = 9.109 x 10 -28g• Charge = -1• Mass = 0 amu
• Atoms are small but nuclei are smaller
• Diameter of a penny has 810 million copper atoms
Atomic Number
• Number of protons in an atom• Electrically neutral atoms have the
same number of electrons as protons
• Ions are formed by gaining or losing electrons
Atomic Mass
• The mass of the nucleus, number of protons and neutrons.
• It is an average of all the isotopes masses
Isotopes• Same number of Protons but
different numbers of neutrons• Mass number is the sum of the
protons and the neutrons• Isotopes have the same chemical
properties• Violates Dalton’s atomic theory
Masses of Atoms• 1 amu = 1/12 mass of a 12C atom
• 99% Carbon 12C
• 1% Carbon 13C
• Average atomic mass of C is 12.01 amu
• Mass number is for one atom
• Listed as a decimal on the periodic table
Nuclear Symbol
• Hyphen notation
• Li - 7
Today’s Objectives
• Review History of the atom• Review the following
– Know the name, location, charge, and relative mass of each of the subatomic particles in an atom
– Know that the atomic number is the number of protons in the nucleus of an atom, and is unique to each element.
– Understand that isotopes are atoms of the same element that differ in the number of neutrons in the nucleus, and therefore differ in mass.
– Know the mass number is, and be able to use it to correctly designate isotopes using both hyphen notation and nuclear symbols
• Know the difference between a neutral atom and an ion is the number of electrons, the charge of the ion is the difference between the number of protons and neutrons
• For any given atom or ion, be able to determine the number of each subatomic particles.
IONS
• Same number of protons but a different number of electrons
• Charged particles because the number of electrons (-) is either greater than or less than the number of protons (+)
• H+
• Ions are determined by there place on the periodic table.
Practice
• Determine the number of subatomic particles for the following:– He – C -14– Na+
– O-2
Nuclear Reactions• Nuclear reactions involve the nucleus
of the atom
• Radioactivity is the spontaneous emission of radiation from an atom
• Nuclear reactions change elements involved
Alpha Particle
• Alpha particle
– Helium nucleus with no electrons
– Will bounce off of paper and skin
– +2 charge
Beta Particle• Beta particle
– High energy electron– Come from the decay
of a neutrons– Will penetrate skin– Blocked by
aluminum and Plexiglass
– -1 charge
• Gamma Rays
– High energy wave
– No charge
– No mass
– Penetrates skin, damages cells and mutates DNA
– Blocked by lead
Gamma Radiation
Nuclear Stability• Most elements have a
stable nucleus• A strong nuclear force
holds protons and neutrons together
• Neutrons act as the “glue” holding the protons together
Nuclear Equations• Scientists use a nuclear equation when
describing radioactive decay
• The mass number and atomic number must add up to be the same on both sides of the equation
Beta Decay• Beta decay results in an increase in
the atomic number
Practice• Write the nuclear equation of the
alpha decay of Radon – 226• Write the nuclear equation of the
alpha decay of Gold - 185
Practice• Write the nuclear equation of the
beta decay of Iodine - 131• Write the nuclear equation of the
beta decay of Sodium - 24
Chapter 24Applications of Nuclear
Chemistry
Half Life• Radioisotopes are radioactive
isotopes of elements (not all isotopes are radioactive)
• A half-life is the amount of time it takes for one half of a sample to decay.
• http://lectureonline.cl.msu.edu/~mmp/applist/decay/decay.htm
Beta Decay of Phosphorous - 32
Radiocarbon Dating• Carbon - 14 undergoes beta decay• Half life of 5,730 years• Used to approximate ages 100 –
30,000 years• Other radioisotopes are used to
measure longer periods of time
Parent Daughter Half Change in...
Carbon-14 Nitrogen-14 5730 years
Uranium-235 Lead-207 704 million years
Uranium-238 Lead-206 4,470 million years
Potassium-40 Argon-40 1,280 million years
Thorium-232 Lead-208 14,010 million years
Rubidium-87 Strontium-87 48,800 million years
Nuclear Bombardment• Nuclear scientists make nuclei
unstable by being bombarded with particles
• Also known as particle accelerators or “atom smashers”
Radiation• SI units are in Curies (Ci)• One Curies is amount of nuclear
disintegrations per second from one gram of radium
• Also measured in rem (Roentgen equivalent for man
• Over 1000 rem is fatal• Detected by a Geiger counter
Nuclear Power• Nuclear Reactors use fission of Uranium-
235 as source of energy• A large nucleus is split into two smaller
nuclei• A small amount of mass is converted to a
tremendous amount of energy• ~1 lb Uranium 235 = 1 million gallons of
gasoline• http://people.howstuffworks.com/nuclear-power2.htm
Nuclear Fusion
• 2 atomic nuclei fuse releasing a tremendous amount of energy
Nuclear Weapons• Source of
energy is Plutonium or Hydrogen
• Can be fusion or fission
Gun-triggered fission bomb (Little Boy - Hiroshima),
Implosion-triggered fission bomb (Fat Man - Nagasaki),
http://people.howstuffworks.com/nuclear-bomb5.htm
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