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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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