Understanding Atoms, Molecules & Ions in Chemistry

1. Chapter 2Atoms, Molecules, and Ions

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3. ATOMS, Molecules, & Ions

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

5. 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. PLAY MOVIE

6. Atomic number, Z 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

7. 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

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

9. Boron in Death Valley • Death Valley has been a major source of borax and other boron-containing minerals. • Borax was transported out of Death Valley in wagons pulled by teams of 20 mules.

10. 11B 10B Isotopes • Atoms of the same element (same Z) but different mass number (A). • Boron-10 has 5 p and 5 n: 105B • Boron-11 has 5 p and 6 n: 115B

11. Hydrogen Isotopes Hydrogen has _____ isotopes 1 proton and 0 neutrons, protium 11H 1 proton and 1 neutron, deuterium 21H 1 proton and 2 neutrons, tritium radioactive 31H

12. Isotope Composition

13. Isotopes & Their Uses Heart scans with radioactive technetium-99. 9943Tc Emits gamma rays

14. Masses of Isotopesdetermined with a mass spectrometer See Active Figure 2.3

15. Mass spectrum of C6H5Br

16. 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 19.9% 10B and 80.1% 11B. That is, 11B is 80.1 percent abundant on earth. • For boron atomic weight = 0.199 (10.0 u) + 0.801 (11.0 u) = 10.8 u

17. 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 = ______________

18. Periodic Table • Dmitri Mendeleev (1834-1907) 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.

19. Periods in the Periodic Table PLAY MOVIE

20. Groups/Families in the Periodic Table PLAY MOVIE

21. Regions of the Periodic Table

22. Element Abundance C O Al Si Fe http://www.webelements.com/

23. Hydrogen Shuttle main engines use H2 and O2 PLAY MOVIE

24. Group 1A: Alkali MetalsLi, Na, K, Rb, Cs PLAY MOVIE Reaction of potassium + H2O Cutting sodium metal

25. Group 2A: Alkaline Earth Metals Be, Mg, Ca, Sr, Ba, Ra Magnesium Magnesium oxide PLAY MOVIE

26. Group 3A: B, Al, Ga, In, Tl Cu Al Al resists corrosion (here in nitric acid). Gallium is one of the few metals that can be liquid at room temp.

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

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

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

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

31. Group 6A: O, S, Se, Te, Po Sulfuric acid dripping from snot-tite in cave in Mexico Elemental S has a ring structure.

32. Group 7A: HalogensF, Cl, Br, I, At PLAY MOVIE

33. Group 8A: Noble Gases He, Ne, Ar, Kr, Xe, Rn

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

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

36. NaCl, salt Molecules, Ions & Their Compounds PLAY MOVIE Ethanol, C2H6O Buckyball, C60

37. Compounds & Molecules • COMPOUNDSare a combination of 2 or more elements in definite ratios by mass. • The character of each element is lost when forming a compound. • MOLECULESare the smallest unit of a compound that retains the characteristics of the compound.

38. MOLECULAR FORMULAS • Formula for glycine is C2H5NO2 • In one molecule there are • 2 C atoms • 5 H atoms • 1 N atom • 2 O atoms

39. WRITING FORMULAS • Can also write glycine formula as • H2NCH2COOH to show atom ordering • or in the form of a structural formula

40. MOLECULAR MODELING Structural formula of glycine Ball & stick Space-filling

41. Molecular & Ionic Compounds Fe N Iron-porphyrin NaCl

42. ELEMENTS THAT EXIST AS MOLECULES Allotropes of C

43. ELEMENTS THAT EXIST AS DIATOMIC MOLECULES

44. ELEMENTS THAT EXIST AS POLYATOMIC MOLECULES S8 sulfur molecules White P4 and polymeric red phosphorus

45. IONS AND IONIC COMPOUNDS

46. IONS AND IONIC COMPOUNDS • IONSare atoms or groups of atoms with a positive or negative charge. • Taking away an electron from an atom gives a CATION with a positive charge • Adding an electron to an atom gives an ANION with a negative charge.

47. Forming Cations & Anions A CATIONforms when an atom losesone or more electrons. An ANION forms when an atom gainsone or more electrons PLAY MOVIE PLAY MOVIE F + e- f F- Mg f Mg2+ + 2 e-

48. See Active Figure 2.17

49. PREDICTING ION CHARGES See Figure 2.18 In general • metals (Mg) lose electrons fcations • nonmetals (F) gain electronsfanions

50. -4 -3 -2 -1 +1 +2 Charges on Common Ions +3 By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.