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CHAPTER 2 AP CHEM

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2.2 REVIEW 1.Atomic Number, Mass Number, Atomic Symbol Atomic number, Z, is the number of protons An atomic symbol represents the element The mass number is equal to protons +neutrons

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2.3 ISOTOPES Definition: Two or more forms of the same element containing different numbers of neutrons. Isotopes of an element have the same chemical properties but differing mass numbers. Examples:

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3. Mass Spectrometer and percent abundance A device that measures both the individual mass numbers and the percentages of each isotope that exist in a sample of an element. The percentage an isotope makes up of the entire isotope that exists in nature.

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2.4 ATOMIC WEIGHT 1. Atomic mass or Atomic weight one amu (atomic mass unit) = exactly 1/12 of the mass of a carbon-12 atom Atomic weight (mass) is the weighted average of the masses of an elements’ isotopes *in chemistry the terms atomic weight and atomic mass are used interchangeably

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EX2.1 Boron exists in two naturally, occurring isotopes. B-10 ( 10.016 amu) makes up 18.83% of each natural sample of this element. The remaining 81.17% of the sample is B-11 (11.013 amu). What atomic mass would be calculated for this mixture of isotopes? Solve by multiplying isotope mass by % Boron -10(10.016) (0.1883) = 1.8860 Boron -11(11.013) (0.8117) = +8.9393 10.825 amu Keep 5 sig figs – consider percent as exact number

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EX2.2 Li (6.01512 amu) which accounts for 7.42% of the total and 7 Li which accounts for the remaining amount. If the mass of lithium is shown as 6.942 on the periodic table, what is the mass of the Li -7 isotope? (answer = 7.016 amu) The two natural isotopes of Lithium are 6 Li (6.01512 amu) which accounts for 7.42% of the total and 7 Li which accounts for the remaining amount. If the mass of lithium is shown as 6.942 on the periodic table, what is the mass of the Li -7 isotope? (answer = 7.016 amu)

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4. MOST ABUNDANT NATURAL ISOTOPE Hydrogen is the most abundant natural isotope

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2.5 ATOMS AND THE MOLE 1. Definition: the amount of a substance that contains as many “representative particles” ( atoms, molecules, or other particles) as there are atoms in 12grams of carbon-12 atoms. 1 mole = 6.022045 x 10 23 r.p.’s

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ANALOGY Bakery count 1 dozen = 12 donuts Chemists use moles like dozens to make things more manageable http://www.youtube.com/watch?v=g_BelGwRxG8

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3. Avogadro’s Number 1 mole = 6.022 x 10 23 particles 4. Second Definition The mass of 1 mole of atoms of a pure element in grams is equal to the atomic mass of that element in amu

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EX 2.3 One mole of sulfur contains 6.022 x 10 23 atoms of sulfur and has a mass of 32.06 grams. What is the mass of one atom of sulfur? (Use 32.1 to determine sig. figs.) (answer = 5.33x10 -23 g)

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EX 2.4 How many sulfur atoms are present in 1.00 grams of sulfur? (answer = 1.88x10 22 atoms S)

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EQUIVALENCIES AND CONVERSION FACTORS FormulaFormula mass (amu) Molar Mass (g) H 1.00794 amu 1.00794 g/mole H 2 = g/mole H 2 O = g/mole H 2 SO 4 = g/mole

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SAMPLE MOLE PROBLEMS Ex2.5 How many moles are equivalent to 5.00 g CaCO 3 ? (Add molar masses of calcium, oxygen and carbon present to get the molar mass) 5.00 grams CaCO 3 1 mole CaCO 3 = 0.0500 moles CaCO 3 100.1 g CaCO 3 Ex2.6 A microchemical experiment requires 0.0100 moles of Al(NO 3 ) 3. How many grams is this? (answer = 2.13 g)

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MORE MOLE PROBLEMS Ex. 2.7 For exactly 1.000 g of carbon disulfide (CS 2 ), how many molecules are present? How many atoms of sulfur? 1.000 g CS 2 1 mole CS 2 6.022 x 10 23 molecules CS 2 = 7.903 x10 21 molc. CS 2 76.2 g CS 2 1 mole CS 2 7.903 x10 21 molc. CS 2 Ex2.8 A sample of sulfur hexafluoride (SF 6 ) contains 1.69 x 10 22 atoms of fluorine. What is the mass of the sample? (answer = 2.48x10 47 g SF 6 )

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THE PERIODIC TABLE 1.History Mendeleev, 1869 - developed the first periodic table by identifying similarities among the elements; based on increasing atomic mass Periodic Law – The properties of elements repeat when arranged by atomic number (updated after Moseley’s work) Moseley, 1913 - organized the P.T. by atomic number

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THE PERIODIC TABLE Groups or families – columns down the P.T. Periods or series – rows across P.T. Metals - on the left side of the staircase, metalloids - along the staircase, nonmetals - on the right side of the staircase Main group elements – the “A” groups of P.T. Transition metals – in the middle Lanthanides and Actinides – bottom double rows

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Specific Family Names to Memorize: Specific Family Names to memorize: Group 1 – Alkali metals Group 2 – Alkaline Earth metals Group 17 (7A) – Halogens Group 18 (8A) – Noble gases

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PERIODIC TABLE http://www.youtube.com/watch?v=SmwlzwGMMwc

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Coulomb’s Law – a helpful tool in explaining P.T. trends Page 93 of the textbook The magnitude of the electrostatic force of interaction between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distances between them.forcecharges Two charges of the same sign=repulsive force; Two charges of opposite sign=attractive force; At least one is neutral=no force Like charges repel opposite charges attract

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Coulomb’s Law video

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The Equation

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Applying Coulomb’s Law to P.T. Throughout our study this year, we will apply Coulomb’s Law to support observed properties such as melting point and boiling point The product of the charges and the force of attraction is directly proportional The square of the distances and the force of attraction is inversely proportional

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HOMEWORK CHAPTER 2 HW#1 -21, 23, 25, 27, 29, 47 Composition Atoms, Isotopes HW#2 - 31, 33, 35 Atomic Symbols Wkst HW #3 – 37, 39, 59, 61, 62, 63 HW #4 - Mole Relationships Wkst. HW #5 - 43, 45, 57 PT

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