A TOMS AND E LEMENTS

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