Chapter 3 Atomic Theory. Early Theories 4 elements.
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Chapter 3Atomic Theory
Early Theories• 4 elements
Democritus(460 - 370 BC)
• Greek philosopher• Atomos –
indivisible particles
• Atoms are the smallest particle that retains the chemical identity
The Greeks Used Logic
• The Greeks also believed in a combination of elements to make new things.
• For example: Water and Earth = Mud
• Mud might just seem like a nuisance to us, but back then it was a building material.
• Fire and Earth made Lava.
• If you are curious check out the Little Alchemy app (game) that can be found in Google Apps. It is a fun game.
Jabir Ibn Haiyan (700? - 803 AD)
• Father of Chemistry
• Practiced Alchemy
• Discovered metals
Antoine Lavoisier(1743 - 1794)
• Law of Conservation of Matter
Joseph Louis Proust(1754-1826)
• Law of Constant Composition
John Dalton (1766 - 1844)
• Atomic Theory
• This was the true start of our modern theory of matter.
Dalton’s Theory
• Dalton’s ideas were a good start.
• However, we need to look at one of his postulates more closely.
• He stated that “All atoms of the same atom are identical…”
• He didn’t know about isotopes. The neutron wasn’t discovered for another 130 years.
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
Thomson’s Model
• This lead directly to the idea of electrons and was a major advancement in atomic theory.
• Sometimes this theory is called “Raisins in a Plum Pudding.”
Robert Millikan(1838-1953)
• Determined charge & mass of electron
Henri Becquerel(1852 - 1908)
• Uranium exposes film
Marie (1867-1934) & Pierre Curie (1859-1906)
• Discovered radioactivity elements
• Radioactive decay
Earnest Rutherford(1871 - 1937)
• Discovered radioactivity particles
• Discovered Nucleus
• Solar system model of atom
Discovery of particles
gold foil experiment
Rutherford’s Gold Foil Experiment
• There are animations on the website so that you can get a better visual of the experiment.
• Rutherford’s experiment was truly a marvel.
• It answered a lot of questions and gave a good framework for future investigations.
• Remember that it was still a theory – there is a long way to go in understanding an atom.
Early Atomic Theory• At this point, this completes our look at the
early contributors into Atomic Theory and Structure.
• You were given a lot of names, but here are the ones I want you to focus on:
• Democritus, Dalton, Thompson, Rutherford
• When we get to other topics, we will explore a few more of them in detail such as Becquerel and the Curies.
Study Guide Help
• To assist you in your preparation, take note that I will not be asking much if anything about the following scientists:
• Ben Franklin, Joseph Proust, Michael Faraday
• Robert Millikan, Jabir Ibn Haiyan, and Antoine Lavoisier might get a short question or two on a test or quiz.
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
Quarks, Quarks, Quarks (1950s – present)
• 6 quarks have been discovered that make up protons and neutrons
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
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
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
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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