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Chemistry Chapter 3

Chemistry Chapter 3. Atoms: The Building Block of Matter. 3:1 The Atom: From Philosophical Idea to Physical Theory. The idea of the atom was first devised by Democritus in 530 B.C. In 1808, an English school teacher and scientist named John Dalton proposed the modern atomic theory.

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Chemistry Chapter 3

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

  2. 3:1 The Atom: From Philosophical Idea to Physical Theory • The idea of the atom was first devised by Democritus in 530 B.C. • In 1808, an English school teacher and scientist named John Dalton proposed the modern atomic theory.

  3. Dalton’s Atomic Theory • All matter is made of atoms • All atoms of any element are the same • Atoms of different elements are different (size, mass, and other properties) • Atoms of different elements can combine to form compounds • In chemical reactions, atoms are not made, destroyed, or changed (subdivided) • In any compound, the numbers and kinds of atoms remain the same – atoms combine in whole number ratios • In a chemical reaction atoms are combined separated or rearranged

  4. Changes • All atoms of any element are not always the same – different mass • Atoms can be changed (subdivided) – quarks

  5. Modern Atomic Theory • All matter is composed of atoms • Atoms of any one element differ in properties from atoms of another element

  6. 3.2 Structure of the Atom • Atom is the smallest particle of an element that retains the chemical properties of that element • J.J. Thomson’s cathode ray experiment revealed the existence of the electron

  7. Milikan’s oil drop experiment confirmed that electron had a negative charge & a very small mass Earnest Rutherford’s gold foil experiment revealed the nucleus and that the nucleus had a positive charge

  8. In 1932, James Chadwick discovered a third type of sub-atomic particle which he named the neutron. Neutrons help stabilize the protons in the atom's nucleus.

  9. Quiz: • 1. Dalton's idea that all matter is composed of atoms was first introduced in ancient Greece by the philosopher named? • A. Hippocrates.B. Aristotle.C. Democritus.D. Pythagoras. • 2. Magnesium will react with bromine to form a compound called magnesium bromide, MgBr2. If 10.00 g of magnesium is mixed with 65.75 g of bromine and allowed to react, you would expect the mass of the products of the reaction to be? A. 75.75 g.B. less than 75.75 g.C. more than 75.75 g.D. unpredictable. 3. According to Dalton's atomic theory, atoms cannot? A. have mass.B. be destroyed.C. combine with other atoms.D. differ from one element to another.

  10. 4. Which of the following statements describes a part of the atomic theory that has been modified in the 200 years since Dalton proposed it? A. All matter is composed of atoms.B. Atoms cannot be subdivided, created, or destroyed.C. In chemical reactions, atoms are combined, separated, or rearranged.D. Nothing has been modified. • 5. Since Dalton proposed the atomic theory, scientists have discovered that atoms of a given element A. can have different masses.B. all have the same mass.C. do not combine in whole-number ratios with atoms of other elements.D. consist of smaller atoms.

  11. 3.3 Counting Atoms • ATOMIC NUMBER (Z) the number of protons an atom contains in its nucleus. ex: Carbon Z=6 Oxygen Z=8 Uranium Z=92

  12. · Different elements have different numbers of neutrons in their nuclei but all atoms of the same element always have the same number of protons. • · Atoms of the same element with different numbers of neutrons are called nuclides or isotopes. • · Nuclides differ only in mass. They act alike chemically. • ·      Carbon-12 6 p+ and 6 no • ·      Carbon-14 6 p+ and 8 no

  13. MASS NUMBER (atomic mass) • symbol = A • ·      the total number of nucleons in an atom • ·      Therefore: A = p+ + no • ·      To determine the number of neutrons in an atom, • A = p+ + no • - Z = p+ no

  14. Atomic Mass Unit (u) •      relative mass - mass of an atom • compared to the mass of C-12 The masses recorded on the periodic table are averages for all the known isotopes of that element.

  15. Ex: In a sample of 200 carbon atoms, 199 are C-12 and 1 is C-14. What is the average atomic mass of carbon? Avg. A = (mass x abundance) + (mass x abundance) + ... # of atoms in the sample Avg. A = (12 x 199) + (14 x 1) 200 = 12.01

  16. Mole (mol) •       a group of 6.02 x 1023 atoms •       a mole of any type of atom has a mass in grams equal to the atomic mass on the periodic table •     a mole of C has a mass of 12 g •     a mole of O has a mass of 16 g

  17. What is a mole? • SI base unit for amount of a substance • Avogadro’s Number of particles (NA) • 602 000 000 000 000 000 000 000 particles • 6.02 x 1023 particles • 1 mol

  18. Molar Mass • Mass of 1 mole of a pure substance is called the molar mass of that substance: • Atoms = atomic mass • Molecules = molecular mass • Formulas units = formula mass • Ions = formula mass 1 mole of Carbon = 12.0 g 1 mole of H20 = 18.0 g

  19. Mole Conversions: Example 1: How many moles are in 48.0 g of C ? 1 mol C 12.0 g C ? mol C = 48.0 g C = 4.00 mol C

  20. Mole Conversions: Example 2: How many grams are in 6.00 mol of HCl ? 36.5 g HCl 1.0 mol HCl ? g HCl = 6.00 mol HCl = 219 g HCl

  21. Mole Conversions: Example 3: How many atoms are in 3.00 mol of N? 6.02 x 1023 atoms 1.0 mol N ? atoms N = 3.00 mol N = 1.81 x 1024 atoms N

  22. Mole Conversions: Example 4: How many molecules are in 90.0 g of H20? 6.02 x 1023 mole. 1.0 mol H20 ? mole. H20 = 90.0 g H20 1 mol H20 18.0 g H20 = 3.01 x 1024 molecules H20

  23. Problems • P. 87 – 17 – 24, 28

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