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A TOMS AND E LEMENTS

Explore the discovery of radioactivity by Marie Curie and the composition of atoms, including protons, neutrons, and electrons. Learn about isotopes and their uses, counting atoms, and the periodic table.

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A TOMS AND E LEMENTS

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  1. ATOMS AND ELEMENTS

  2. Radioactivity • One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934). • She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

  3. ATOMIC COMPOSITION • Protons • + electrical charge • mass = 1.672623 x 10-24 g • relative mass = 1.007 atomic mass units (amu) • Electrons • negative electrical charge • relative mass = 0.0005 amu • Neutrons • no electrical charge • mass = 1.009 amu

  4. ATOM COMPOSITION The atom is mostly empty space • protons and neutrons in the nucleus. • the number of electrons is equal to the number of protons. • electrons in space around the nucleus. • extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water.

  5. The modern view of the atom was developed by Ernest Rutherford of New Zealand(1871-1937).

  6. Ernest Rutherford Canterbury University in Christchurch, NZ Rutherford laboratory

  7. The modern view of the atom was developed by Ernest Rutherford(1871-1937). Screen 2.9

  8. Atomic number Atom symbol Atomic weight Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z 13 Al 26.981

  9. Atomic Weight • This tells us the mass of one atom of an element relative to one atom of another element. • OR — the mass of 1000 atoms of one relative to 1000 atoms of another. • For example, an O atom is approximately 16 times heavier than an H atom. • Define one element as the standard against which all others are measured • Standard = carbon

  10. Mass Number, A • C atom with 6 protons and 6 neutrons is the mass standard • = 12 atomic mass units • Mass Number (A) = # protons + # neutrons • A boron atom can have A = 5 p + 5 n = 10 amu

  11. 11B 10B Isotopes • Atoms of the same element (same Z) but different mass number (A). • Boron-10 (10B) has 5 p and 5 n • Boron-11 (11B) has 5 p and 6 n

  12. Isotopes & Their Uses Bone scans with radioactive technetium-99.

  13. Isotopes & Their Uses The tritium content of ground water is used to discover the source of the water, for example, in municipal water or the source of the steam from a volcano.

  14. Masses of Isotopesdetermined with a mass spectrometer

  15. 11B 10B Isotopes • Because of the existence of isotopes, the mass of a collection of atoms has an average value. • Average mass = ATOMIC WEIGHT • Boron is 20% 10B and 80% 11B. That is, 11B is 80 percent abundant on earth. • For boron atomic weight = 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu

  16. Isotopes & Atomic Weight • Because of the existence of isotopes, the mass of a collection of atoms has an average value. • 6Li = 7.5% abundant and 7Li = 92.5% • Atomic weight of Li = ______________ • 28Si = 92.23%, 29Si = 4.67%, 30Si = 3.10% • Atomic weight of Si = ______________

  17. Counting Atoms Mg burns in air (O2) to produce white magnesium oxide, MgO. How can we figure out how much oxide is produced from a given mass of Mg?

  18. Counting Atoms Chemistry is a quantitative science—we need a “counting unit.” MOLE 1 mole is the amount of substance that contains as many particles (atoms, molecules) as there are in 12.0 g of 12C.

  19. Particles in a Mole Avogadro’s Number Amedeo Avogadro 1776-1856 6.02214199 x 1023 There is Avogadro’s number of particles in a mole of any substance.

  20. Molar Mass 1 mol of 12C = 12.00 g of C = 6.022 x 1023 atoms of C 12.00 g of 12C is its MOLAR MASS Taking into account all of the isotopes of C, the molar mass of C is 12.011 g/mol

  21. One-mole Amounts

  22. PROBLEM: What amount of Mg is represented by 0.200 g? How many atoms? Mg has a molar mass of 24.3050 g/mol. How many atoms in this piece of Mg? = 4.95 x 1021 atoms Mg

  23. Periodic Table • Dmitri Mendeleev developed the modern periodic table. Argued that element properties are periodic functions of their atomic weights. • We now know that element properties are periodic functions of their ATOMIC NUMBERS. • See CD-ROM, Screen 2.16.

  24. Periods in the Periodic Table

  25. Groups in the Periodic Table

  26. Regions of the Periodic Table

  27. Element Abundance C O Al Si Fe http://www.webelements.com/webelements/elements/text/Si/geol.html

  28. Hydrogen Shuttle main engines use H2 and O2 The Hindenburg crash, May 1939.

  29. Group 1A: Alkali Metals Reaction of potassium + H2O Cutting sodium metal

  30. Group 2A: Alkaline Earth Metals Magnesium Magnesium oxide

  31. Calcium Carbonate—Limestone Champagne cave carved into chalk in France The Appian Way, Italy

  32. Group 3A: B, Al, Ga, In, Tl Aluminum Boron halides BF3 & BI3

  33. Gems & Minerals • Sapphire: Al2O3 with Fe3+ or Ti3+ impurity gives blue whereas V3+ gives violet. • Ruby: Al2O3 with Cr3+ impurity

  34. Group 4A: C, Si, Ge, Sn, Pb Quartz, SiO2 Diamond

  35. Group 5A: N, P, As, Sb, Bi White and red phosphorus Ammonia, NH3

  36. Phosphorus • Phosphorus first isolated by Brandt from urine, 1669

  37. Group 6A: O, S, Se, Te, Po Sulfuric acid dripping from snot-tite in cave in Mexico Sulfur from a volcano

  38. Group 7A: F, Cl, Br, I, At

  39. XeOF4 Group 8A: He, Ne, Ar, Kr, Xe, Rn • Lighter than air balloons • “Neon” signs

  40. Transition Elements Lanthanides and actinides Iron in air gives iron(III) oxide

  41. Colors of Transition Metal Compounds Nickel Cobalt Copper Zinc Iron

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