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

http://proxify.com/p/011111A0000110/http/education.jlab.org/atomtour/listofparticles.html

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