1 © 2006 Brooks/Cole - Thomson Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 2 Atoms and Elements © 2006 Brooks/Cole Thomson Lectures written by John Kotz

2 © 2006 Brooks/Cole - Thomson A TOMS AND E LEMENTS

3 © 2006 Brooks/Cole - Thomson Radioactivity One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ).One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ). She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

4 © 2006 Brooks/Cole - Thomson Types of Radioactive Emissions

5 © 2006 Brooks/Cole - Thomson Types of Radioactive Emissions

6 © 2006 Brooks/Cole - Thomson ATOMIC COMPOSITION ProtonsProtons –+ electrical charge –mass = x g –relative mass = atomic mass units (u) ElectronsElectrons – negative electrical charge –relative mass = u NeutronsNeutrons – no electrical charge –mass = u

7 © 2006 Brooks/Cole - Thomson ATOM COMPOSITION protons and neutrons in the nucleus.protons and neutrons in the nucleus. the number of electrons is equal to the number of protons.the number of electrons is equal to the number of protons. electrons in space around the nucleus.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.extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water. The atom is mostly empty space

8 © 2006 Brooks/Cole - Thomson The modern view of the atom was developed by Ernest Rutherford of New Zealand ( ).

9 © 2006 Brooks/Cole - Thomson Ernest Rutherford Canterbury University in Christchurch, NZ Rutherford laboratory

10 © 2006 Brooks/Cole - Thomson The modern view of the atom was developed by Ernest Rutherford ( ). Screen 2.9

11 © 2006 Brooks/Cole - Thomson Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z 13 Al Atomic number Atom symbol Atomic weight

12 © 2006 Brooks/Cole - Thomson Atomic Weight This tells us the mass of one atom of an element relative to one atom of another element.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.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.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 measuredDefine one element as the standard against which all others are measured Standard = carbonStandard = carbon

13 © 2006 Brooks/Cole - Thomson Mass Number, A C atom with 6 protons and 6 neutrons is the mass standardC atom with 6 protons and 6 neutrons is the mass standard = 12 atomic mass units (u)= 12 atomic mass units (u) Mass Number (A) = # protons + # neutronsMass Number (A) = # protons + # neutrons A boron atom can have A = 5 p + 5 n = 10 uA boron atom can have A = 5 p + 5 n = 10 u

14 © 2006 Brooks/Cole - Thomson Boron in Death Valley Death Valley has been a major source of borax and other boron-containing minerals.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.Borax was transported out of Death Valley in wagons pulled by teams of 20 mules.

15 © 2006 Brooks/Cole - Thomson Isotopes Atoms of the same element (same Z) but different mass number (A).Atoms of the same element (same Z) but different mass number (A). Boron-10 has 5 p and 5 n: 10 5 BBoron-10 has 5 p and 5 n: 10 5 B Boron-11 has 5 p and 6 n: 11 5 BBoron-11 has 5 p and 6 n: 11 5 B 10 B 11 B

16 © 2006 Brooks/Cole - Thomson Hydrogen Isotopes Hydrogen has _____ isotopes 11H11H11H11H 21H21H21H21H 31H31H31H31H 1 proton and 2 neutrons, tritium radioactive 1 proton and 1 neutron, deuterium 1 proton and 0 neutrons, protium

17 © 2006 Brooks/Cole - Thomson Isotope Composition IsotopeElectronsProtonsNeutrons Sulfur-32 Bromine- 79

18 © 2006 Brooks/Cole - Thomson Isotopes & Their Uses Heart scans with radioactive technetium Tc Emits gamma rays

19 © 2006 Brooks/Cole - Thomson Masses of Isotopes determined with a mass spectrometer

20 © 2006 Brooks/Cole - Thomson Mass spectrum of C 6 H 5 Br

21 © 2006 Brooks/Cole - Thomson Isotopes Because of the existence of isotopes, the mass of a collection of atoms has an average value.Because of the existence of isotopes, the mass of a collection of atoms has an average value. Average mass = ATOMIC WEIGHTAverage mass = ATOMIC WEIGHT Boron is 19.9% 10 B and 80.1% 11 B. That is, 11 B is 80.1 percent abundant on earth.Boron is 19.9% 10 B and 80.1% 11 B. That is, 11 B is 80.1 percent abundant on earth. For boron atomic weightFor boron atomic weight = (10.0 u) (11.0 u) = 10.8 u = (10.0 u) (11.0 u) = 10.8 u 10 B 11 B

22 © 2006 Brooks/Cole - Thomson Isotopes & Atomic Weight Because of the existence of isotopes, the mass of a collection of atoms has an average value.Because of the existence of isotopes, the mass of a collection of atoms has an average value. 6 Li = 7.5% abundant and 7 Li = 92.5% 6 Li = 7.5% abundant and 7 Li = 92.5% –Atomic weight of Li = ______________ 28 Si = 92.23%, 29 Si = 4.67%, 30 Si = 3.10% 28 Si = 92.23%, 29 Si = 4.67%, 30 Si = 3.10% –Atomic weight of Si = ______________

23 © 2006 Brooks/Cole - Thomson Counting Atoms Mg burns in air (O 2 ) to produce white magnesium oxide, MgO. How can we figure out how much oxide is produced from a given mass of Mg?

24 © 2006 Brooks/Cole - Thomson Counting Atoms Chemistry is a quantitative science—we need a “counting unit.” 1 mole is the amount of substance that contains as many particles (atoms, molecules) as there are in 12.0 g of 12 C. MOLE 518 g of Pb, 2.50 mol

25 © 2006 Brooks/Cole - Thomson Particles in a Mole x Avogadro’s Number There is Avogadro’s number of particles in a mole of any substance. Amedeo Avogadro

26 © 2006 Brooks/Cole - Thomson Molar Mass 1 mol of 12 C = g of C = x atoms of C g of 12 C is its MOLAR MASS Taking into account all of the isotopes of C, the molar mass of C is g/mol

27 © 2006 Brooks/Cole - Thomson One-mole Amounts

28 © 2006 Brooks/Cole - Thomson PROBLEM: What amount of Mg is represented by g? How many atoms? Mg has a molar mass of g/mol. = 4.95 x atoms Mg How many atoms in this piece of Mg?

29 © 2006 Brooks/Cole - Thomson Periodic Table Dmitri Mendeleev developed the modern periodic table. Argued that element properties are periodic functions of their atomic weights.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.We now know that element properties are periodic functions of their ATOMIC NUMBERS. See CD-ROM, Screen 2.16.See CD-ROM, Screen 2.16.

30 © 2006 Brooks/Cole - Thomson Periods in the Periodic Table

31 © 2006 Brooks/Cole - Thomson Groups/Families in the Periodic Table

32 © 2006 Brooks/Cole - Thomson Regions of the Periodic Table

33 © 2006 Brooks/Cole - Thomson Element Abundance Fe C Al O Si

34 © 2006 Brooks/Cole - Thomson HydrogenHydrogen Shuttle main engines use H 2 and O 2

35 © 2006 Brooks/Cole - Thomson Group 1A: Alkali Metals Li, Na, K, Rb, Cs Cutting sodium metal Reaction of potassium + H 2 O

36 © 2006 Brooks/Cole - Thomson Magnesium Magnesium oxide Group 2A: Alkaline Earth Metals Be, Mg, Ca, Sr, Ba, Ra

37 © 2006 Brooks/Cole - Thomson Group 3A: B, Al, Ga, In, Tl Al resists corrosion (here in nitric acid). Gallium is one of the few metals that can be liquid at room temp. CuAl

38 © 2006 Brooks/Cole - Thomson Gems & Minerals Sapphire: Al 2 O 3 with Fe 3+ or Ti 3+ impurity gives blue whereas V 3+ gives violet.Sapphire: Al 2 O 3 with Fe 3+ or Ti 3+ impurity gives blue whereas V 3+ gives violet. Ruby: Al 2 O 3 with Cr 3+ impurityRuby: Al 2 O 3 with Cr 3+ impurity

39 © 2006 Brooks/Cole - Thomson Group 4A: C, Si, Ge, Sn, Pb Quartz, SiO 2 Diamond

40 © 2006 Brooks/Cole - Thomson Group 5A: N, P, As, Sb, Bi White and red phosphorus Ammonia, NH 3

41 © 2006 Brooks/Cole - Thomson Phosphorus Phosphorus first isolated by Brandt from urine, 1669

42 © 2006 Brooks/Cole - Thomson Group 6A: O, S, Se, Te, Po Sulfuric acid dripping from snot-tite in cave in Mexico Elemental S has a ring structure.

43 © 2006 Brooks/Cole - Thomson Group 7A: Halogens F, Cl, Br, I, At

44 © 2006 Brooks/Cole - Thomson Group 8A: Noble Gases He, Ne, Ar, Kr, Xe, Rn

45 © 2006 Brooks/Cole - Thomson Transition Elements Lanthanides and actinides Iron in air gives iron(III) oxide

46 © 2006 Brooks/Cole - Thomson Colors of Transition Metal Compounds Iron Cobalt Nickel CopperZinc