Woods Chem-1 Lec Atoms, Ions, Mole (std) Page 1 ATOMIC THEORY, MOLECULES, & IONS

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1 Woods Chem-1 Lec Atoms, Ions, Mole (std) Page 1 ATOMIC THEORY, MOLECULES, & IONS Proton: A positively charged particle in the nucleus Atomic Number: We differentiate all elements by their number of protons. Atomic Number = Number of Protons» If you change the number of protons, you change the element (e.g. radioactive decay: Uranium decays to Lead) Neutron: Neutral particle of almost the same mass as the proton. Electron: The mass of the electron is nearly 1/2,000 th that of the proton and neutron. J.J. Thompson: Cathode ray tube experiments, rays coming from the cathode were negatively charged particles no matter what material the cathode was made of. By deflecting the rays with electrical and magnetic charges, he was able to calculate a mass to charge ratio of the electron. Since atoms in their elemental state are electrically neutral, there must be one negatively charged particle for each proton. In a Neutral Atom» Number of Protons = Number of Electrons. Atomic Mass: Since the mass of the electron is negligible, the mass of an atom comes from the Protons + Neutrons. Ernest Rutherford: Gold foil experiments: Deflected the alpha particles Proved there must be a very small, very dense nucleus which contains nearly all of the atom's mass. Mass = #Neutrons + #Protons When a number is listed at the upper left of an element it is the mass of a specific isotope (see below). Mass H He Na Mg Cl I #Prot #Nutr #Elect Ion: An atom or molecule with a positive or negative charge. It is always the # of electrons that change NOT the number of protons. Charge: An ion has a charge because there are either more or less electrons than protons. It is the electron structure that causes chemicals to react the way they do. Elements react to Gain, Lose, or Share enough electrons to get to eight in their outer shell. Na Na + (Group I) Mg Mg 2+ (Group II) Na Mg Na + Mg 2+ F F (Group VII) O O 2 (Group VI) F O F O 2 These elements react because they want to have a stable electron configuration like Neon (10 e ), the nearest noble gas. IONS: NaCl, MgCl 2 Mg 3 N 2 Na + + Cl NaCl Na (s) Extremely Reactive Metal Cl 2(g) Very Poisonous Gas Yet after reacting together -- they become a crystalline compound which is necessary in our diet. ISOTOPES: Atoms of the same element which have a different mass. The difference is the Number of Neutrons. Mass H H H C C Na Na #Prot #Nutr

2 Woods Chem-1 Lec Atoms, Ions, Mole (std) Page 2 Element Protons Neutrons Mass # Electrons Net Charge N F WEIGHTED ATOMIC MASS: The Average Mass of All Isotopes of an atom -- as it occurs in nature. Carbon 12 became the standard 1 AMU = 1 / 12 the mass of 12 C atom = g (MOLE: = 1 / ) 1 AMU is so close to the mass of each proton/neutron that we often say the mass of protons/neutrons equals 1AMU. Mass of Proton = x g Neutron = x g Electron = x g Weighted Averages: (Ave of )» (4+5+6) 3 = 5» (33.3% 4) + (33.3% 5) + (33.3% 6) = 5 But what if each compound isn t present in an equal amount? 7 Diatomic Molecules: H + N to F to I (H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 )» 40% 4 X, 50% 5 X, 10% 6 X 90% 12 C, 10% 14 C» A compound contains the following isotopes: % has a mass of g, and the rest has a mass of g. What is the Average Atomic Mass, Accurate to mg? ( IN grams ACCURATE to mg) ELEMENTS: Unfortunately, the most common have the oldest names - names which have been around since antiquity, and therefore aren't a part of any scientific pattern. Antimony Sb Stibium Copper Cu Cuprum Gold Au Aurum Iron Fe Ferrum Lead Pb Plumbum Mercury Hg Hydrargyrum Potassium K Kalium Silver Ag Argentum Sodium Na Natrium Tin Sn Stannum Tungsten W Wolfram Co = Cobalt CO = Carbon monoxide Make sure that upper case letters are used correctly.

3 Woods Chem-1 Lec Atoms, Ions, Mole (std) Page 3 The MOLE A Mole (mol): The amount of material that contains as many basic particles (Atoms, Molecules, or Formula Units) as there are atoms in exactly 12 g of 12 C. The mole is just a number think of it as Dozen. You can have a dozen eggs, shoes, apples just as you could have a mole of eggs, shoes, apples molecules or atoms» Also known as Avogadro's Number. One Mole of O 2 (32.00g), one mole of CO 2 (44.01g), and one H 2 O (18.02g) all have the same number of molecules. Molar Mass (MM): Grams per Mol ( g / mol ) of an atom, a molecule, or an ionic formula unit. Calculating Molar Mass: Sum of the individual molar masses for each atom in the compound. Round off to FOUR Significant Figures when calculating individual molar mass. This is important for our class and many people will miss problems because of improper significant figures. Take ALL molar mass for EACH ELEMENT from the periodic table using four significant figures. MAKE SURE your Total Mass for a compound is rounded to Four Sig Figs before you use it in a problem. O = g/mol, not S = g/mol, not H = g/mol Ba = g/mol» Calculate MM (molar mass) for NaCl, Al 2 S 3, Na 2 SO 4 and Ba 3 (PO 4 ) 2 : NaCl 1 Na = Na 2 SO 4 Na 1 Cl = S» O Al 2 S 3 Al Mg(NO 3 ) 2 Mg S N O Molecular Mass (Covalent Molecule ) vs. Formula Mass (Ionic Formula Unit ) Mass A» Mass B A + 2 B» C + 3 D grams A» mol A» mol B» grams B 1 mol A 2mol B zzz.z g g A x x x = xx.xx g 1mol A 1mol B ( ) g B

4 Woods Chem-1 Lec Atoms, Ions, Mole (std) Page 4 CO 2 = g/mol Understand: g mol then Molecules then Oxygen Atoms 22.5 g CO 2 molecules CO g CO 2 O atoms 22.5 g CO 2 g O» How many moles of Mg(NO 3 ) 2 are in a g sample? How many O atoms are in a g sample? How many grams of oxygen in grams of Mg(NO 3 ) 2? When does the mole ( ) represent atoms vs. molecules?? Look at the Molar Mass; does it reflect an atomic mass or a molecular mass (or FU)? IMPORTANT: Remember not to start a new problem using a rounded number!! You should ALWAYS carry 1-2 digits more than your significant figures. 7 Diatomic Molecules: H + N F I (H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 )

5 Woods Chem-1 Lec Atoms, Ions, Mole (std) Page 5» How many nitrogen molecules are there in grams of nitrogen?» A 5-grain aspirin tablet contains g of acetylsalicylic acid, C 9 H 8 O 4 (MM = g/mol). How many molecules of acetylsalicylic acid are in one tablet? How many atoms of carbon per tablet? IMPORTANT: We are discussing oxygen that is within a compound; therefore we do not consider the molar mass to be that of the diatomic elemental form, O 2 which is g/mol.» How many: Grams of Chlorine in 5.0 g PbCl 2? {(207.2) + (2 x 35.45) = g/mol} Grams of Hydrogen in 4.50 mol H 2 SO 4? Grams of Hydrogen in 5.45 x molecules NH 3?

6 Woods Chem-1 Lec Atoms, Ions, Mole (std) Page 6 Percent (%) Composition» What is the % composition of each element in Mg(NO 3 ) 2? Mg» N» O»» A salt contains 56.58% K, 8.68% C, and 34.73% O. What is the empirical formula? Convert the percentages to grams (100% equivalent to 100 grams). K» C» O» Empirical Formula»» Propylene has a MM of g/mol, and contains 85.7% C and 14.3% H. What are the EF & MF? C» H» Empirical Formula» Molecular Formula»

7 Woods Chem-1 Lec Atoms, Ions, Mole (std) Page 7 Ba»» A salt contains 68.44% Ba, 10.29% P, and 21.27% O. What is the empirical formula? P» O» Empirical Formula» 0.25, 0.33, 0.50, 0.67, 0.75: Important fractions for empirical formulas or equation ratios.» The density of gold is 19.3 g/ml. If you had 1.55 gal of gold, how many gold atoms would it contain?

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