1 Modern Chemistry Chapter 3 Atoms: The Building Block of Matter

2 Chapter Vocabulary Law of conservation of mass Law of definite proportions Law of multiple proportions Atom Nuclear forces Atomic number Isotope Mass number nuclide Atomic mass unit Average atomic mass Mole Avogadro’s number Molar mass

Chapter 3 Section 1 Atoms: Ideas to Theory pages Section 1 Atoms: From Philosophical Idea to Scientific Theory

Chapter 3 Section 1 Atoms: Ideas to Theory pages Foundation of Chemical Atomic Theory Law of Conservation of Mass –Mass is neither created nor destroyed during ordinary chemical reactions or physical changes

Chapter 3 Section 1 Atoms: Ideas to Theory pages Law of Conservation of Mass Image p. 69*

Chapter 3 Section 1 Atoms: Ideas to Theory pages Law of Conservation of Mass Image p. 69*

Chapter 3 Section 1 Atoms: Ideas to Theory pages Foundation of Chemical Atomic Theory Law of Definite Proportions –A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or the source of the compound.

Chapter 3 Section 1 Atoms: Ideas to Theory pages Foundation of Chemical Atomic Theory Law of Multiple Proportions –If two or more different compounds are composed of the same two elements then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers.

Chapter 3 Section 1 Atoms: Ideas to Theory pages Law of Multiple Proportions Image p. 69*

Chapter 3 Section 1 Atoms: Ideas to Theory pages Dalton’s Atomic Theory 1. All matter is composed of extremely small particles called atoms

Chapter 3 Section 1 Atoms: Ideas to Theory pages Dalton’s Atomic Theory 2. Atoms of a given element are identical in size, mass and other properties; atoms of different elements differ in size, mass and other properties.

Chapter 3 Section 1 Atoms: Ideas to Theory pages Dalton’s Atomic Theory 3. Atoms cannot be subdivided, created or destroyed.

Chapter 3 Section 1 Atoms: Ideas to Theory pages Dalton’s Atomic Theory 4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

Chapter 3 Section 1 Atoms: Ideas to Theory pages Dalton’s Atomic Theory 5. In chemical reactions, atoms are combined, separated or rearranged.

Chapter 3 Section 1 Atoms: Ideas to Theory pages Modern Atomic Theory Leucippus Democritus Atomic Theory Tested by experiment and modified with new discoveries and experiments

Chapter 3 Section 2 The Structure of the Atom pages Section 2 The Structure of the Atom

Chapter 3 Section 2 The Structure of the Atom pages Discovery of the Electron Cathode Ray Tube Experiment - Thompson Observations –Cathode Rays are deflected a magnetic field. –Cathode rays are deflected from a negatively charged object. –Charge to mass ratio is always the same for the cathode rays.

Chapter 3 Section 2 The Structure of the Atom pages CaTHODE Ray Tube Movie Animation

Chapter 3 Section 2 The Structure of the Atom pages Discovery of the Electron Cathode Ray Tube Experiment - Thompson Conclusion –Cathode rays are composed of negatively charged particles –Named “electrons”

Chapter 3 Section 2 The Structure of the Atom pages Discovery of the Electron Oil Drop Experiment - Millikan –Measured the charge of the electron –Calculated the mass of an electron x kg

Chapter 3 Section 2 The Structure of the Atom pages Discovery of the Electron Inferences –Atoms are neutral, so there must be a positive charge. –Electrons are small, so there must be other particles.

Chapter 3 Section 2 The Structure of the Atom pages Discovery of the Electron Plum Pudding Model –Negative electrons were spread evenly throughout the positive charge.

Chapter 3 Section 2 The Structure of the Atom pages Discovery of the Atomic Nucleus Gold Foil Experiment – Rutherford et. al –Hypothesis: Alpha particles would pass through with slight deflection. –Observation: 1 in 8000 particles were deflected back to the source. –Conclusion: The atom contains a small densely packed bundle of matter with a positive charge –Named the “nucleus”

Chapter 3 Section 2 The Structure of the Atom pages Gold Foil Animation

Chapter 3 Section 2 The Structure of the Atom pages Gold Foil Animation

Chapter 3 Section 2 The Structure of the Atom pages Gold Foil Experiment Image p. 75

Chapter 3 Section 2 The Structure of the Atom pages Discovery of the Atomic Nucleus Relative size of the nucleus

Chapter 3 Section 2 The Structure of the Atom pages Composition of The Atomic Nucleus Nuclei contain protons and neutrons Neutral because number of protons equal number of electrons Each element has a different number of protons in their nucleus –The number of protons determines the atom’s identity Nuclear forces hold protons & neutrons together

Chapter 3 Section 2 The Structure of the Atom pages Properties of Subatomic Particles p. 76

Chapter 3 Section 2 The Structure of the Atom pages Gold Foil Experiment Photo

Chapter 3 Section 2 The Structure of the Atom pages Gold Foil Experiment Photo

Chapter 3 Section 2 The Structure of the Atom pages Thompson and Rutherford Photo

Chapter 3 Section 3 Counting Atoms pages Section 3 Counting Atoms

Chapter 3 Section 3 Counting Atoms pages Atomic Number The number of protons of each atom of that element Identifies the element

Chapter 3 Section 3 Counting Atoms pages Isotopes Atoms of the same element that have different masses Isotopes of hydrogen –Protium 1p + 0n 0 –Deuterium 1p + 1n 0 –Tritium 1p + 2n 0 Isotopes do not differ significantly in their chemical behavior

Chapter 3 Section 3 Counting Atoms pages Mass Numbers Mass numbers = # of p + + # of n 0 of a specific isotope Examples –Protium 1p + + 0n 0 = 1 –Deuterium 1p + + 1n 0 = 2 –Tritium 1p + + 2n 0 = 3

Chapter 3 Section 3 Counting Atoms pages Designating Isotopes Hyphen notation –name of element – mass number –Hydrogen – 3 Nuclear symbol mass number atomic number

Chapter 3 Section 3 Counting Atoms pages Number of neutrons in an atom neutrons = mass number – atomic number Problem page 77 How many p +, e - and n 0 are there in an atom of chlorine-37? 17 p + 17e- 20n 0 (37-17) Practice Problems page 78 #1-3 Nuclide – a general term for a specific isotope of an element

Chapter 3 Section 3 Counting Atoms pages Relative Atomic Mass One atom, carbon-12, is set as a standard All masses are expressed in relation to this standard 1 atomic mass unit = 1/12 the mass of a carbon-12 atom

Chapter 3 Section 3 Counting Atoms pages Relative Atomic Mass Examples –Hydrogen – 1 = amu –Oxygen – 16 = amu –Magnesium – 24 = amu p + = amu, n 0 = amu, e - = amu Relative mass and mass number are close in value but not the same

Chapter 3 Section 3 Counting Atoms pages Average Atomic Mass The weighted average of the atomic masses of naturally occurring isotopes of an element AM = (mass isotope x abundance)+(mass isotope x abundance)+... Example –Copper Cu-63:.6915 x amu = Cu-65:.3085 x amu = amu percent relative mass

Chapter 3 Section 3 Counting Atoms pages The Mole An amount of a substance that contains as many particles as there are atoms in exactly 12 g carbon-12. Similar to a dozen or a pair or a gross x carbon-12 atoms = 12 grams of carbon-12 Avogadro’s number = x particles

Chapter 3 Section 3 Counting Atoms pages Molar mass The mass of one mole of a pure substance Unit = g/mol On the periodic table, use 4 sig. figs.

Chapter 3 Section 3 Counting Atoms pages Gram-Mole Conversions The conversion factor for gram-mole conversion is molar mass. What is the mass, in grams, of 3.50 moles of Cu? –222 grams Cu OR g mol g

Chapter 3 Section 3 Counting Atoms pages Practice Problems page 85 1.What is the mass in grams of 2.25 mol of the element iron? 2.What is the mass in grams of mol of the element potassium? 3.What is the mass in grams of mol of the element sodium? 4.What is the mass in grams of 16.3 mol of the element nickel? p g Fe 14.7 g K g Na 957 g Ni

Chapter 3 Section 3 Counting Atoms pages Conversions Image p. 84

Chapter 3 Section 3 Counting Atoms pages Gram-Mole Conversions The conversion factor for gram-mole conversion is molar mass. A Chemist produced 11.9 g of Al. How many moles of Al were produced? –0.411 moles Al OR g mol g

Chapter 3 Section 3 Counting Atoms pages Practice Problems page 83 1.How many moles of calcium are in 5.00 g of calcium? 2.How many moles of gold are in 3.60 x g of gold? 3.How many moles of zinc are in g of zinc? p mol Ca 1.83 x mol Au 8.18 x mol Zn

Chapter 3 Section 3 Counting Atoms pages Conversions with Avogadro’s Number The conversion factor for particle-mole conversion is Avogadro’s number. How many moles of silver are in 3.01 x atoms of silver –0.500 moles Ag OR 6.022x10 23 atoms 1 mol 6.022x10 23 atoms 1 mol

Chapter 3 Section 3 Counting Atoms pages Practice Problems page 84 1.How many moles of lead are 1.50 x atoms of lead? 2.How many moles of tin are in 2500 atoms of tin? 3.How many atoms of aluminum are in 2.75 mol of aluminum? p. xx 2.49 x mol Pb 4.2 x mol Sn 1.66 x atoms Al

Chapter 3 Section 3 Counting Atoms pages Conversions with Avogadro’s Number The conversion factor for particle-mole conversion is Avogadro’s number. What is the mass, in grams, of 1.20x10 18 atoms of Cu? –1.27 x g Cu OR 6.022x10 23 atoms 1 mol 6.022x10 23 atoms 1 mol

Chapter 3 Section 3 Counting Atoms pages Practice Problems page 85 1.What is the mass in grams of 7.5 x atoms of nickel? 2.How many atoms of sulfur are in 4.00 g of sulfur? 3.What mass of gold contains the same number of atoms as 9.0 g of aluminum? p. xx 7.3 x g Ni 7.51 x atoms S 66 g Au

Chapter 3 Section 3 Counting Atoms pages Conversions Image p. 84