Atoms, Molecules and Ions Chapter 2

Foundations of Atomic Theory _________________________________________ –Mass is neither created nor destroyed. The total mass of a compound must be the same as the total mass of individual elements. HgO  Hg + O g 401.2g + 32g

Dalton’s Atomic Theory (1808) 1. 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. 2. Compounds are composed of atoms of more than one element. The relative number of atoms of each element in a given compound is always the same. 3. Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions.

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. The electrode is named by what type of particle it attracts –Cathode: Negative (-) –Anode: Positive (+) When connected to electric current the remaining gas glowed forming a ___________________________. The beam always originated at the _____________ electrode and toward the _____________electrode.

1897 JJ Thomson used magnets to deflect the beam proving that particles had a ___________________________.

Now with the knowledge of electrons, and knowing the atom is neutral, there must be a particle that is positive to balance the negative charge. A small paddle wheel was placed inside and it rolled toward the anode, providing evidence that some _____________ MUST BE STRIKING THE WHEEL to make it move.

Plum Pudding Model

Robert A. Millikan Performed the ____________________ Determined the exact:

e - charge = x C e - mass = 9.10 x g Measured Charge of e - (1923 Nobel Prize in Physics)

Radioactivity Becquerel –discovered _______________________ uranium would expose photographic plates in the dark –The properties of an element changed as it gave off radiation Curie –Discovered radium and polonium The radioactive emissions of ___________, ___________ and __________rays were identified.

(Uranium compound)

Ernest Rutherford’s Gold Foil Experiment Set up Gold Foil with a detection sheet around it. Set up radioactive source emitting alpha particles. ____________________shot at gold foil.

Rutherford’s Gold Foil Experiment

__________particles went through the gold foil __________particles _____________back Rutherford: It’s like shooting a cannon at a piece of tissue paper and having it bounce back at you!

Gold Foil Conclusions

Rutherford’s Model of the Atom

Goldstein and Wien Cathode Ray Tube with perforated cathode Discovered collection of positively charged particles **

Chadwick’s Experiment Found that alpha particles shot at beryllium made a beam form The beam had the same mass of a proton but was electrically neutral **

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 **

Bohr’s Model of the Atom

SUBATOMIC PARTICLES

Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons X A Z H 1 1 H (D) 2 1 H (T) 3 1 U U Isotopes:

How many protons, neutrons, and electrons are in C 14 6 ? How many protons, neutrons, and electrons are in C 11 6 ? Do You Understand Isotopes?

Period Group

Molecule: an aggregate of two or more atoms in a definite arrangement held together by chemical bonds H2H2 H2OH2ONH 3 CH 4 diatomic molecule: polyatomic molecule:

An _______ is an atom, or group of atoms, that has a net positive or negative charge. cation – anion – Na 11 protons 11 electrons Na + 11 protons 10 electrons Cl 17 protons 17 electrons Cl - 17 protons 18 electrons

monatomic ion: polyatomic ion:

Do You Understand Ions? How many protons and electrons are in Al ? 3+3+ How many protons and electrons are in Se ?

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 1/12 mass of Carbon atom Periodic table lists weighted average atomic masses of elements (like a GPA calculation) Relative Atomic Mass

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