Unit 3.1
An atom is the smallest physical particle of an element that still retains the properties of that element.
At sea level, one cubic centimeter of air (size of a sugar cube, or marble) will have 45 billion atoms within it. 45,000,000,000
One century after Dalton, Viennese scientist Ernst Mach wrote that atoms cannot be perceived by the senses they are things of thought. Many scientists that made contributions to atomic structure J.J. Thomson, Robert Millikan, Chadwick, Ernest Rutherford, and Neils Bohr, Erwin Schrödinger.
1. All elements are composed of tiny particles called atoms. 2. Atoms of the same element are identical. Atoms of different elements are always different. 3. Atoms of different elements can chemically combine in fixed ratios to form compounds.
Law of Conservation of Mass Mass is not created or destroyed in a chemical reaction or physical change Law of Constant Composition Law of Multiple Proportions Cr 2 O 3 CrO 3
Atoms are solid and indivisible.
Electrons J.J. Thomson in 1897 Particles deflected in Cathode Ray tube Negative one charge Very small mass 1/2000 that of the lightest atom
Thompson passed electric current through gases in a glass tube. The result was a glowing beam flowing from the negative side to the positive side.
Glowing ray (cathode ray) was attracted to a positive magnet on the side of the tube. Beam must be negatively charged.
Thompson hypothesized that all atoms had such negative charges within. (plum pudding model) Later, scientists proved that atoms contained both positive and negative charges (which balance each other out).
Born in New Zealand. Terrible at mathematics. Diligent problem solver. First to discover the power of the atom, power to make bombs that could make this old world vanish in smoke.
Ernest Rutherford 1911 Gold Foil Experiment using alpha particles nucleus
Shot radioactive particles through a sheet of gold foil. Most went straight through, but others were knocked off course or bounced back. Like shooting a fifteeninch shell at a sheet of paper and having it bounce off.
Nucleus compact center of the atom where protons and neutrons are located Nucleus has very little of the atom s volume, but contains most of the atom s mass.
Chadwick found that the mass of an atom is greater than the mass of protons plus electrons. Neutrons portion of an atom with no charge Protons, neutrons, and electrons are called subatomic particles.
Proton Mass equal to H Positive one charge Found in the nucleus Neutron Mass equal to H No charge Found in the nucleus Electron Mass 1/2000 of H Negative one charge Found in the e - cloud
Electrons orbit the nucleus in orbits, like a solar system. Planetary Model
Born in Vienna, Austria University of Berlin professor Nobel Prize 1933 Based on waves of light and probability. Quantum Mechanical Model like a shot gun blast.
Atomic structure
Atoms of different elements have different structures. Elements differ because their atoms contain different numbers of protons! Atomic Number number of protons in the atom
The number of protons determine the properties (identity) of the element. Atoms are neutral so the number of protons = number of electrons How many protons does Hydrogen have? ANSWER: 1 How many electrons does hydrogen have? Answer: 1 How many protons and electrons does silver have? Answer: 47
Electrons have negligible mass compared to protons and neutrons. Mass of a neutron is approximately equal to mass of a proton. Mass Number - number of protons plus number of neutrons in an atom.
Hyphen notation Name of elementmass number Examples Silver-108 Carbon-12 Why is it not necessary to show the atomic number? Nuclear symbol Mass # element symbol Atomic # It is not necessary to put the atomic number Examples: 108 Ag 12 C 6
Mass number (p + + n o ) Element symbol Atomic number (number of p + )
Beryllium 5 neutrons Mass Number? Sodium 12 neutrons Mass Number? Gold 118 neutrons Mass Number =?
How many protons, neutrons, and electrons in each? Magnesium-23 Answer: protons= 12 neutrons= mass atomic =11 electrons = 12 119 Sn Answer: protons = 50, neutrons = 69, e - = 50
Atoms of the same element with different number of neutrons Chemically equivalent Most elements occur as a mixture of isotopes Same atomic #, different mass#
One amu (atomic mass unit) is defined as 1/12 the mass of a Carbon-12 atom 1 amu is approx. equal to the mass of a proton or neutron
Atomic masses found on periodic table are averages of all isotopes of that element Based on abundance (weighted mass) To calculate the atomic mass of an element, multiply the mass of each isotope by its natural abundance (expressed as a decimal), and then add the products.
Chlorine is a mixture of Cl-35 and Cl-37. 75.77% Cl-35 (35) 24.23% Cl-37 (37) 0.7577 x 35 amu = 26.50 amu 0.2423 x 37 amu = 8.957 amu + Added together 35.45 amu
Carbon-12 98.89% Carbon-13 1.11% Atomic Mass?
18 8 8 18 Arsenic 75 33 75 Phosphorus 15 31 16
Unit 3.3
The mole is the SI unit for amount of substance (counting number) 1 dozen = 12 1 gross = 144 1 ream = 500 1 mole = 6.02 x 10 23
6.02 x 10 23 is called Avogadro s Number in honor of the Italian chemist Amadeo Avogadro (1776-1855). I didn t discover it. Its just named after me! Amadeo Avogadro
1 mole of books = 6.02 x 10 23 books 1 mole of atoms = 6.02 x 10 23 atoms 1 mole of molecules = 6.02 x 10 23 molecules Conversion factor: 6.02 x 10 23 atoms or 1 mol (use to convert atoms >mol) 1 mole 6.02 x 10 23 atoms If you have 1 mole of books and 1 mole of feathers you have the same amount of each, but does 1 mole of books have the same mass as 1 mole of feather?
Mass in grams of 1 mole of a substance 1 carbon-12 atom has a mass of 12 amu but 1 mole of carbon atoms (6.02 x 10 23 atoms) has a mass of 12 g The molar mass of carbon is 12 g/mol The molar mass of any atom is its average atomic mass (you can find it on the periodic table)
What is the molar mass of Ca 40.1 g/mol S 32.1 g/mol Conversion factor: 40.1 g Ca or 1 mole Ca (use to convert mass <->mol) 1 mol Ca 40.1 g Ca
How many grams of lithium are in 3.50 moles of lithium? 3.50 mol Li 6.94 g Li 1 mol Li = 24.3 g Li
How many moles of lithium are in 18.2 grams of lithium? 18.2 g Li 1 mol Li 6.94 g Li = 2.62 mol Li
How many atoms of lithium are in 3.50 moles of lithium? 3.50 mol Li 6.022 x 10 23 atoms Li 1 mol Li = 2.11 x 10 24 atoms Li
How many atoms of lithium are in 18.2 g of lithium? 18.2 g Li 1 mol Li 6.022 x 10 23 atoms Li 6.94 g Li 1 mol Li (18.2)(6.022 x 10 23 )/6.94 = 1.58 x 10 24 atoms Li