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A TOMS AND E LEMENTS

A TOMS AND E LEMENTS. 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. ATOMIC COMPOSITION.

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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. ATOMCOMPOSITION The atom is mostly empty space • protons and neutrons in the nucleus. • the number of electrons is equal to the number of protons. • Electrons are extremely small and occupy the space around the nucleus.

  5. Scientists • Chadwich Thomsom Becquerel Rutherford Curie Millikan Bohr

  6. The modern view of was developed by Ernest Rutherford the “Nuclear Atom”

  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. • Define one element as the standard against which all others are measured • Standard = carbon • For example, an O atom is approximately 16 times heavier than an H atom.

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

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

  12. Masses of Isotopesdetermined with a mass spectrometer

  13. 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

  14. 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 = ______________

  15. 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.

  16. 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.

  17. 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

  18. One-mole Amounts

  19. 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

  20. Periodic Table • Dmitri Mendeleev developed the modern periodic table. Argued that element properties are periodic functions of their atomic weights. • Today: element properties are periodic functions of their ATOMIC NUMBERS.

  21. Periodic Table History • Henry Mosley- -Grouped elements in order of atomic number -credited with modern periodic table Came up with Period Law- -physical and chemical properties of elements are a periodic function of their atomic numbers

  22. Modern Periodic Table • Glen Seaborg- -Grouped elements according to their electron configurations -credited with periodic table as it looks today

  23. Modern Periodic Table • Groups (families)o a vertical column i of elements. determined by # of valenceelectrons

  24. Modern Periodic Table • Periods (a) n horizontal row of elements. -determined by the electron’s energy level.

  25. NOBLE GASES NONMETALS METALLOIDS METALS

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

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

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

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

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

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

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

  33. Group 7A:HALOGENS F, Cl, Br, I, At

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

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

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

  37. 1A 2A 8A 3A 4A 5A 6A 7A Groups/ Families 1 2 3 4 5 6 7 “B” or Transition Metals Halogens Noble Gases Alkali Alkaline Earth Rare Lanthanides Earth Actinides Periods

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