Chapter 3 Atomic 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 ( BC) Greek philosopher Atomos – indivisible particles Atoms are the smallest particle that retains the chemical identity

Jabir Ibn Haiyan (700? AD) Father of Chemistry Practiced Alchemy Discovered metals

Lavoisier ( ) Law of Conservation of Matter

Joseph Louis Proust ( ) Law of Constant Composition

Dalton ( ) 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 ( ) Two types of charge positive (+) and negative (-)

Michael Faraday ( ) Atoms are related to electricity

J.J. Thomson ( ) Cathode Ray Tube (CRT) stream of electrons Plum Pudding Model

cathode ray tube

Robert Millikan ( ) Determined charge & mass of electron

Becquerel ( ) Uranium exposes film

Marie ( ) & Pierre Curie ( ) Discovered radioactivity elements Radioactive decay

Rutherford ( ) 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 ( ) Discovered protons (+) in the nucleus Rearranged periodic table

Sir James Chadwick ( ) 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 x C Mass = x g Charge +1 Mass = 1 amu

Neutrons Make up the nucleus Charge 0 Mass = x g 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 x C Mass = x g 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 12 C atom 99% Carbon 12 C 1% Carbon 13 C Average atomic mass of C is 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 Write the nuclear equation of the beta decay of Sodium - 24

Chapter 24 Applications 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. cay/decay.htmhttp://lectureonline.cl.msu.edu/~mmp/applist/de cay/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

ParentDaughterHalf Change in... Carbon-14 Nitrogen years Uranium-235Lead million years Uranium-238Lead-2064,470 million years Potassium-40Argon-401,280 million years Thorium-232Lead-20814,010 million years Rubidium-87Strontium-8748,800 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 power2.htmhttp://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),