Atoms, Molecules and Ions Chapter 3

Foundations of Atomic Theory Law of conservation of mass: Antoine Lavoisier Mass is neither created nor destroyed. The total mass of a compound must be the same as the total mass of individual elements. Law of definite composition: Joseph Proust a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound HgO  Hg + O 433.2 g 401.2g + 32g Sugar: 42.1 % Carbon 51.4 % Oxygen 6.5 % Hydrogen Whether you have a teaspoon or a truckload!

Law of Conservation of Mass 16 X 8 Y + 8 X2Y Law of Conservation of Mass

Law of multiple proportions: John Dalton Applies to different compounds made from the same elements The mass ratio for one of the elements that combines with a fixed mass of the other element can be expressed as a whole number ratio. H2O H2O2 Water Peroxide 2g H 2g H 16g O 1:2 Ratio 32g O

Law of Multiple Proportions 2 Law of Multiple Proportions

Dalton’s Atomic Theory (1808) Elements are composed of extremely small particles called atoms. All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements Atoms cannot be subdivided, created or destroyed

Dalton’s Atomic Theory (1808) cont’d Atoms of different elements combine in simple whole-number ratios to form chemical compounds. 5. Chemical reactions only involve the rearrangement of atoms.

JJ Thomson’s Cathode Ray Tube Negatively Charged Electrode Positively Charged Electrode

Cathode Ray Tube Scientists studied the flow of electric current in a glass vacuum tube with electrodes at each end. When connected to electric current the remaining gas glowed forming a BEAM OF LIGHT. The beam always originated at the NEGATIVE electrode and toward the POSITIVE electrode. 1897 JJ Thomson used magnets to deflect the beam proving that particles had a NEGATIVE CHARGE.

JJ THOMSON DISCOVERED A NEGATIVE PARTICLE CALLED THE ELECTRON!

CRT Video

Plum Pudding Model

Plum Pudding OR Chocolate Chip Cookie

Robert A. Millikan Performed the Oil Drop Experiment Determined the exact charge of an electron

Thomson’s charge/mass of e- = -1.76 x 108 C/g Measured Charge of e- (1923 Nobel Prize in Physics) e- charge = -1.60 x 10-19 C Thomson’s charge/mass of e- = -1.76 x 108 C/g e- mass = 9.10 x 10-28 g

Oil Drop Experiment Video

Ernest Rutherford’s Gold Foil Experiment Set up Gold Foil with a detection sheet around it. Set up radioactive source emitting alpha particles. ALPHA PARTICLES shot at gold foil. MOST particles went through the gold foil SOME particles BOUNCED back

Rutherford’s Gold Foil Experiment

Gold Foil Conclusions The atom is made up of mostly EMPTY SPACE The center of the atom contains a POSITIVE CHARGE Rutherford called this positive bundle of matter the NUCLEUS

Gold Foil Experiment Video

Rutherford’s Model of the Atom atomic radius ~ 100 pm = 1 x 10-10 m nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m If the atom is the size of Giants Stadium Then the nucleus is a marble on the 50 yard line

Ob-scertainer You can’t see something, but you know it’s there… you feel it moving… How is it moving? Do your best to determine the movement of the “particle” in your containers

Ob-scertainer Solutions #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12

**DISCOVERED ENERGY LEVELS!! Niels Bohr – 1913 Developed a new diagram of the atom Electrons can only be at certain energies Electrons must gain a specific amount of energy to move to a higher level, called a quantum **DISCOVERED ENERGY LEVELS!!

Bohr’s Model of the Atom

Subatomic Particles (Table 2.1) mass p = mass n = 1840 x mass e-

X H H (D) H (T) U Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei Mass Number X A Z Element Symbol Atomic Number H 1 H (D) 2 H (T) 3 U 235 92 238

Do You Understand Isotopes? How many protons, neutrons, and electrons are in C 14 6 ? 6 protons, 8 (14 - 6) neutrons, 6 electrons How many protons, neutrons, and electrons are in C 11 6 ? 6 protons, 5 (11 - 6) neutrons, 6 electrons

Period Group

A diatomic molecule contains only two atoms A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds H2 H2O NH3 CH4 A diatomic molecule contains only two atoms H2, N2, O2, Br2, HCl, CO A polyatomic molecule contains more than two atoms O3, H2O, NH3, CH4

cation – ion with a positive charge An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. Na 11 protons 11 electrons Na+ 11 protons 10 electrons anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Cl- 17 protons 18 electrons Cl 17 protons 17 electrons

A monatomic ion contains only one atom Na+, Cl-, Ca2+, O2-, Al3+, N3- A polyatomic ion contains more than one atom OH-, CN-, NH4+, NO3-

How many protons and electrons are in Do You Understand Ions? How many protons and electrons are in Al 27 13 ? 3+ 13 protons, 10 (13 – 3) electrons How many protons and electrons are in Se 78 34 2- ? 34 protons, 36 (34 + 2) electrons

Relative Atomic Mass Atomic Mass Unit One atom is the standard – Carbon Mass of other elements are based off of the standard Carbon: 6 p and 6 n = 12 amu Atomic Mass Unit 1/12 mass of Carbon atom Periodic table lists weighted average atomic masses of elements (like a GPA calculation)

Calculation AVERAGE Atomic Mass 75% 133Cs 20% 132Cs 5 % 134Cs Steps: 1. Percent to decimal 2. Multiply by mass 3. Add it up!