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Understanding Atoms: The Basis of Modern Chemistry

Explore the foundational principles of atomic theory from Dalton to Modern Atomic Theory, including laws, experiments, and atomic structure. Understand concepts like atomic number, isotopes, molar mass, and the mole. Practice problems and review questions included.

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Understanding Atoms: The Basis of Modern Chemistry

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  1. Chapter 3 • Atoms: The Building Blocks of Matter

  2. The Atomic Theory • Law of conservation of mass • Mass is neither destroyed nor created • Law of definite proportions • Compound is always composed of same proportion of elements • Law of multiple proportions • If two different compounds are composed of the same elements, the two elements form a ratio of small number

  3. Law of Conservation of Mass

  4. Law of Multiple Proportions

  5. Dalton • All matter is composed of atoms • Atoms of an element are identical in size, mass and other properties • Atoms cannot be subdivided, created, or destroyed • Atoms combine in simple whole-number ratios • Atoms are combined, separated, or rearranged in chemical reactions

  6. Modern Atomic Theory • All matter is composed of atoms • Atoms of one element differ in properties from atoms of another element • Atom - smallest particle of an element that retains the chemical properties of that element

  7. Thompson • Current passed through cathode-ray tube • Current produced a stream of particles (cathode ray) that traveled towards the anode • Rays deflected from negatively charged object • Ratio of charge to mass of particles

  8. Milikan • Oil-drop experiment • Charge of electron determined • Calculated mass of electron using ratio of charge to mass

  9. The Electron • Mass of 9.109 x 10-31 kg • Atoms are neutral, so must contain same number of electrons and protons • Electrons mass has negligible effect on total mass of atom

  10. The Nucleus • Rutherford’s gold foil experiment • Thin, gold foil bombarded with α particles • Some α particles deflected • Caused by positively charged nucleus • Volume of nucleus small

  11. Rutherford

  12. Rutherford

  13. The Nucleus • Composed of two particles • Protons • Neutrons • Protons mass = 1.673 x 10-27 kg • 1826 times greater than e- • Nuclear strong force • Holds positive particles together

  14. Atomic Number • Atoms of different elements have different number of protons • Atomic number (Z) • number of protons in the nucleus • Elements arranged in order of their atomic number on periodic table

  15. Mass Number • Total number of protons and neutrons • Ex. Hydrogen Isotopes

  16. Isotopes • Element may contain different number of neutrons • Isotopes have differing mass • Naming • Helium-4 (hyphen notation) • 42Helium (nuclear symbol)

  17. Problems • How many protons, electrons, and neutrons are in an atom of carbon-13? • Write the nuclear symbol for oxygen-16. • How many protons, electrons, and neutrons are in an atom of bromine-80? • Write the nuclear symbol for carbon-13. • Write the hyphen notation for the element that contains 15 electrons and 15 neutrons.

  18. Relative Atomic Masses • Atomic mass unit (amu) • 1/12 the mass of carbon-12 • 1.660 540 x 10-27 kg • Hydrogen-1 = 1 amu • Average atomic mass • Weighted average of atomic masses of isotopes

  19. Average Atomic Mass • Ex. • 25% weigh 2.00 g • 75% weigh 3.00 g • (2.00 g x 0.25) + (3.00 g x 0.75) = 2.75 g

  20. Problem • What is the average atomic mass of copper which consists of 69.17% copper-63 (62.929 598 amu), and copper-65 (64.927 793 amu)?

  21. Problems • Three isotopes of argon occur in nature - Ar-36, Ar-38, Ar-40. Calculate the average atomic mass of argon to two decimal places, given the following relative atomic masses and abundances of each of the isotopes: argon-36 (35.97 amu; 0.337%), argon-38 (37.96 amu; 0.063%), and argon-40 (39.96 amu; 99.600%).

  22. The Mole • Amount of substance that contains as many particles as there are atoms in exactly 12 g of carbon-12 • Counting unit like dozen • Dozen = 12 • Mole = 6.022 x 1023 • Avogadro’s number • 6.022 x 1023

  23. Molar Mass • Mass of one mole of pure substance • Units → g/mol • Molar mass = atomic mass in amu

  24. Conversions

  25. Conversions • 1 mol/(6.022 x 1023) atoms • Molar mass/mol

  26. Problems • What is the mass in grams of 3.6 mol of the element carbon, C? • What is the mass in grams of 0.733 mol of the element chlorine, Cl? • How many moles of copper, Cu, are in 3.22 g of copper? • How many moles of lithium, Li, are in 2.72 x 10-4 g of lithium?

  27. Problems • How many moles of carbon, C, are in 2.25 x 1022 atoms of carbon? • How many moles of oxygen, O are in 2 000 000 atoms of oxygen? • How many atoms of sodium, Na, are in 3.80 mol of sodium? • What is the mass in grams of 5.0 x 109 atoms of neon, Ne?

  28. Problems • How many atoms of carbon, C, are in 0.020 g of carbon? • What mass of silver, Ag, contains the same number of atoms as 10.0 g of boron, B? • How many moles of CO2 are in 66.0 g of dry ice, which is solid CO2

  29. Chapter Review • Pg. 89 • 1, 8, 11, 17, 18acd, 20, 21, 22ade, 23abcd

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