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

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

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