AP Notes Chapter 2 Atoms and Elements History of the atom Summed-up Greeks Greeks Democritus and Leucippus - atomos Democritus and Leucippus - atomos Aristotle- elements. Aristotle- elements. Alchemy Alchemy Robert Boyle- experimental definition of element Robert Boyle- experimental definition of element. Lavoisier- Father of modern chemistry. Lavoisier- Father of modern chemistry.

Dalton’s Atomic Theory 1) Elements are made up of atoms 2) Atoms of each element are identical. Atoms of different elements are different. 3) Compounds are formed when atoms combine. Each compound has a specific number and kinds of atom. 4) Chemical reactions are rearrangement of atoms. Atoms are not created or destroyed.

The Atom Dalton (early 1800s) Dalton (early 1800s) indivisible

Gay-Lussac- under the same conditions of temperature and pressure, compounds always react in whole number ratios by volume. Gay-Lussac- under the same conditions of temperature and pressure, compounds always react in whole number ratios by volume. Avagadro- interpreted that to mean Avagadro- interpreted that to mean at the same temperature and pressure, equal volumes of gas contain the same number of particles. at the same temperature and pressure, equal volumes of gas contain the same number of particles. (called Avagadro’s Hypothesis) (called Avagadro’s Hypothesis) A Helpful Observation

Experiments & theories to determine what an atom was John Dalton- atoms indivisible John Dalton- atoms indivisible J. J. Thomson- Cathode ray tubes, electrons J. J. Thomson- Cathode ray tubes, electrons Marie Curie- radioactivity Marie Curie- radioactivity Robert Millikan- electron mass & charge Robert Millikan- electron mass & charge Ernest Rutherford- protons Ernest Rutherford- protons James Chadwick- neutrons James Chadwick- neutrons

Thomson’s Experiment Voltage source +-

Thomson’s Experiment Voltage source +-

n Passing an electric current makes a beam appear to move from the negative to the positive end. Voltage source +- Thomson’s Experiment

Voltage source Thomson’s Experiment By adding an electric field By adding an electric field

Voltage source n By adding an electric field, he found that the moving pieces were negative + - Thomson’s Experiment

The Atom Thompson (~ 1900) Thompson (~ 1900) “plum pudding” model cloud of (+) charge electron (-) charge

Thomsom’s Model Found the electron. Found the electron. Couldn’t find positive (for a while). Couldn’t find positive (for a while). Said the atom was like plum pudding. Said the atom was like plum pudding. A bunch of positive stuff, with the electrons able to be removed. A bunch of positive stuff, with the electrons able to be removed.

Millikan’s Experiment Oil Atomizer Oil droplets Telescope - +

Millikan’s Experiment X-rays X-rays give some electrons a charge.

Millikan’s Experiment Some drops would hover From the mass of the drop and the charge on the plates, he calculated the mass of an electron

Radioactivity Discovered by accident Discovered by accident Henri Bequerel – photographic plates Henri Bequerel – photographic plates Marie Curie – studied & named it Marie Curie – studied & named it Three types Three types alpha- helium nucleus (+2 charge, large mass) alpha- helium nucleus (+2 charge, large mass) beta- high speed electron beta- high speed electron gamma- high energy light gamma- high energy light

James Chadwick Neutrons Neutrons Particles from radioactive polonium hit a beryllium target and produced particle Particles from radioactive polonium hit a beryllium target and produced particle no charge no charge slightly greater mass than the proton slightly greater mass than the proton

Rutherford’s Experiment Used uranium to produce alpha particles. Used uranium to produce alpha particles. Aimed alpha particles at gold foil by drilling hole in lead block. Aimed alpha particles at gold foil by drilling hole in lead block. Since the mass is evenly distributed in gold atoms alpha particles should go straight through. Since the mass is evenly distributed in gold atoms alpha particles should go straight through. Used gold foil because it could be made atoms thin. Used gold foil because it could be made atoms thin.

Lead block Uranium Gold Foil Florescent Screen Rutherford’s Experiment

What he expected Rutherford’s Experiment

Because Rutherford’s Experiment

Because, he thought the mass was evenly distributed in the atom. Rutherford’s Experiment

What he got Rutherford’s Experiment

How he explained it + Atom is mostly empty Atom is mostly empty Small dense, Small dense, positive piece at center. positive piece at center. Alpha particles are deflected by Alpha particles are deflected by it if they get close it if they get close enough. enough. Rutherford’s Experiment

+

Gold Foil Experiment Rutherford (~1911) Nuclear Model Rutherford (~1911) Nuclear Model heavy central (+) nucleus e - “about” nucleus

The Atom Rutherford (~ 1911) Rutherford (~ 1911) heavy central (+) nucleus (e - ) about nucleus Nuclear Model

The Atom Bohr (~ 1913) Bohr (~ 1913) central (+) nucleus e - in allowed orbits Planetary Model n=1 n=2 n=3

Modern View The atom is mostly empty space. The atom is mostly empty space. Two regions Two regions Nucleus- protons and neutrons. Nucleus- protons and neutrons. Electron cloud- region where you might find an electron. Electron cloud- region where you might find an electron.

The Atom Heisenberg, de Broglie, Schroedinger (mid 1920s) Heisenberg, de Broglie, Schroedinger (mid 1920s) e - in regions defined by math functions Quantum Mechanical Model

Sub-atomic Particles Z - atomic number = number of protons determines type of atom. Z - atomic number = number of protons determines type of atom. A - mass number = number of protons + neutrons. A - mass number = number of protons + neutrons. Number of protons = number of electrons if neutral. Number of protons = number of electrons if neutral.

Nuclear Symbols & Notation X A Z Na ←Element Symbol Mass Number→ Atomic Number→ Na 24 11

Isotopes of elements Isotopes are forms of an atom that differ by the number of neutrons Isotopes are forms of an atom that differ by the number of neutrons Mass number is approximation of exact atomic mass of an isotope Mass number is approximation of exact atomic mass of an isotope Atomic mass or atomic weight is the average mass of the isotopes of atoms Atomic mass or atomic weight is the average mass of the isotopes of atoms Isotopic percent abundance or fractional abundance is a description of the proportion of an isotope in a sample of an element Isotopic percent abundance or fractional abundance is a description of the proportion of an isotope in a sample of an element

Atomic Mass Atoms are so small, it is difficult to discuss how much they weigh in grams. Atoms are so small, it is difficult to discuss how much they weigh in grams. Use atomic mass units. Use atomic mass units. an atomic mass unit (amu) is one twelth the mass of a carbon-12 atom. an atomic mass unit (amu) is one twelth the mass of a carbon-12 atom. This gives us a basis for comparison. This gives us a basis for comparison. The decimal numbers on the table are atomic masses in amu. The decimal numbers on the table are atomic masses in amu.

They are not whole numbers Because they are based on averages of atoms and of isotopes. Because they are based on averages of atoms and of isotopes. can figure out the average atomic mass from the mass of the isotopes and their relative abundance. can figure out the average atomic mass from the mass of the isotopes and their relative abundance. add up the percent as decimals times the masses of the isotopes. add up the percent as decimals times the masses of the isotopes.

hydrogen deuterium tritium Isotopes of Hydrogen

Examples There are two isotopes of carbon 12 C with a mass of amu(98.892%), and 13 C with a mass of amu (1.108%). There are two isotopes of carbon 12 C with a mass of amu(98.892%), and 13 C with a mass of amu (1.108%). There are two isotopes of nitrogen, one with an atomic mass of amu and one with a mass of amu. What is the percent abundance of each? There are two isotopes of nitrogen, one with an atomic mass of amu and one with a mass of amu. What is the percent abundance of each?

Atomic Weight = (abundance isotope 1)(weight isotope1) + (abundance isotope 2)(weight isotope2)… or Fractional Abundance Fractional abundance = Percent Abundance 100% Percent Abundance Percent abundance = number of atoms of a given isotope x 100% total number of atoms of all isotopes

A portion of an atom’s mass of protons, neutrons and electrons is converted to energy that holds the atom together. A portion of an atom’s mass of protons, neutrons and electrons is converted to energy that holds the atom together. Einstein gave us ΔE = (Δm)C 2 Einstein gave us ΔE = (Δm)C 2 The loss of this mass as the atom forms is called the mass defect. This missing mass is converted to “binding energy” (BE) The loss of this mass as the atom forms is called the mass defect. This missing mass is converted to “binding energy” (BE) Mass atom = BE + #pro. + #elec. + #neu. Mass atom = BE + #pro. + #elec. + #neu.

Allotrope Different forms of the same element that exist in the same physical state under the same conditions of Temperature & Pressure Carbon Diamond Graphite

GraphiteDiamonds Buckyballs

Periodic Table

Metals Conductors Conductors Lose electrons Lose electrons Malleable and ductile Malleable and ductile

Nonmetals Brittle Brittle Gain electrons Gain electrons Covalent bonds Covalent bonds

Semi-metals or Metalloids

Alkali Metals

Alkaline Earth Metals

Halogens

Transition metals

Noble Gases

Inner Transition Metals

Periodic Table Families or Groups 1A 2A 3A 4A 5A 6A 7A 8A 3B 4B 5B 6B 7B 8B 1B 2B

Periodic Table Periods Lanthanide Series Actinide Series

Periods and Groups or Families

HydrogenHydrogen Shuttle main engines use H 2 and O 2 The Hindenburg crash, May 1939.

Group 1A: Alkali Metals Cutting sodium metal Reaction of potassium + H 2 O Potassium

Magnesium Magnesium oxide Group 2A: Alkaline Earth Metals Magnesium Ablaze!

Calcium Carbonate—Limestone The Appian Way, Italy Champagne cave carved into chalk in France

Group 3A: B, Al, Ga, In, Tl Aluminum Boron halides BF 3 & BI 3

Gems & Minerals Sapphire: Al 2 O 3 with Fe 3+ or Ti 3+ impurity gives blue whereas V 3+ gives violet. Sapphire: Al 2 O 3 with Fe 3+ or Ti 3+ impurity gives blue whereas V 3+ gives violet. Ruby: Al 2 O 3 with Cr 3+ impurity Ruby: Al 2 O 3 with Cr 3+ impurity

Transition Elements Lanthanides and actinides Iron in air gives iron(III) oxide

Colors of Transition Metal Compounds Iron Cobalt Nickel CopperZinc

Group 4A: C, Si, Ge, Sn, Pb Quartz, SiO 2 Diamond

Group 5A: N, P, As, Sb, Bi White and red phosphorus

Phosphorus Phosphorus first isolated by Brandt from urine, 1669 Phosphorus first isolated by Brandt from urine, 1669

Group 6A: O, S, Se, Te, Po Sulfuric acid dripping from snot-tite in cave in Mexico Sulfur from a volcano

Group 7A: F, Cl, Br, I, At Halogen

Group 8A: He, Ne, Ar, Kr, Xe, Rn Lighter than air balloons Lighter than air balloons “Neon” signs “Neon” signs XeOF 4