1. Atoms, Molecules and Ions Chapter 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acknowledgement Thanks to McGraw-Hill Companies, Inc. for allowing usage in the classroom

2. The atomic theory Dalton’s Atomic Theory (1808) 1. Elements are composed of extremely small particles called atoms. 2.All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements. 3.Compounds are formed from atoms of more than one element in a fixed ratio. (Law of Definite Proportions) The ratio of the atoms in any compound is either an integer or a simple fraction. (Law of Multiple Proportions) 4.A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction. Note: Only the nuclear reaction can create or destroy an atom. Atom is electrically neutral. 2.1

4. 2 Dalton’s Atomic Theory

5. 8 X 2 Y 16 X8 Y + 2.1

6. atomic radius ~ 100 pm = 1 x 10 -10 m nuclear radius ~ 5 x 10 -3 pm = 5 x 10 -15 m Rutherford’s Model of the Atom 2.2

8. Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons number of protons = number of electrons X A Z Mass Number Atomic Number Element Symbol 2.3 Atomic number, Mass number and Isotopes

9. Difference between Mass Number and Average Atomic Mass Mass number, different from average atomic mass (or atomic weight), is always a positive integer. -Number of electron is always a positive integer. -Mass number can not be found in the periodic table; while the average atomic mass (Ch. 3) is always listed in the periodic table. -Average atomic mass is calculated by including all isotopes of an atom, and thus always contains decimal digits.

10. 2.3 Isotopes U 235 92 U 238 92 Isotopes are atoms of the same element (X) with different numbers of neutrons (or say mass number) in their nuclei. Example: (1) hydrohen-1, deuterium-2, tritium-3 (2) carbon-12, carbon-13, carbon-14

11. 6 protons, 8 (=14 - 6) neutrons, 6 electrons 6 protons, 5 (=11 - 6) neutrons, 6 electrons Protons, neutrons, and electrons in isotopes 2.3 How many protons, neutrons, and electrons are in C 14 6 ? How many protons, neutrons, and electrons are in C 11 6 ?

12. Period Group Alkali Metal Noble Gas Halogen Alkaline Earth Metal 2.4 The periodic table

13. Molecules and ions

14. Molecular Compound H2H2 H2OH2ONH 3 CH 4 A diatomic molecule contains only two atoms:H 2, N 2, O 2, Br 2, HCl, CO A polyatomic molecule contains more than two atoms:O 3, H 2 O, NH 3, CH 4 2.5

15. cation – ion with a positive charge; – number of protons is greater than number of electrons If a neutral atom loses one or more electrons, it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons, it becomes an anion. An ion is an atom, or group of atoms, that has a net positive or negative charge. Na 11 protons 11 electrons Na + 11 protons 10 electrons Cl 17 protons 17 electrons Cl - 17 protons 18 electrons 2.5 A monatomic ion contains only one atom:Na +, Cl -, Ca 2+, O 2-, Al 3+, N 3- A polyatomic ion contains more than one atom:OH -, CN -, NH 4 +, NO 3 -

16. 13 protons, 10 (= 13 – 3) electrons 34 protons, 36 (= 34 – (-2) = 34 + 2) electrons Calculate protons and electrons in an ion 2.5 How many protons and electrons are in ?Al 27 13 3+ How many protons and electrons are in ?Se 78 34 2-

17. 2.5

18. Ionic compounds consist of a combination of cations and an anions. The most reactive metals and the most reactive nonmetals combine to form ionic compounds. NaCl

19. A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance An empirical formula shows the simplest whole-number ratio of the atoms in a substance H2OH2O H2OH2O molecularempirical C 6 H 12 O 6 CH 2 O O3O3 O N2H4N2H4 NH 2 2.6 Chemical formula

20. Structural formula: Show connection between atoms; The connection is usually shown as lines (one line refers to single bond; two lines as double bonds; three lines as triple bond); tells the most information. Can show the geometry when factor in VSEPR (Ch. 9). Condensed structural formula: Similar to the structural formula but not showing the bond(s); central atom usually referring to carbon is written first and then surrounding atoms. Ball-and-stick-model: Shown geometry but not bond(s) Space-filling model:

21. The formula is always the same as the empirical formula because molecules don’t exit in ionic compounds. That is, ionic compounds only have empirical formulas. Also compounds are electrically neutral. 2.6 Formula of Ionic Compounds

22. 2.6 Al 2 O 3 2 x +3 = +63 x -2 = -6 Al 3+ O 2- CaBr 2 1 x +2 = +22 x -1 = -2 Ca 2+ Br - Na 2 CO 3 1 x +2 = +21 x -2 = -2 Na + CO 3 2- The sum of charges on the cations and anions in each formula unit must be zero. The subscript of cation is numerically equal to the charge on the anion; The subscript of anion is numerically equal to the charge on the cation;

23. 2.7

25. Ionic Compounds *For ionic compound that contains representative metal ion, there is no need to specify the charge on the metal. NaClsodium chloride CaO calcium oxide *For ionic compound that contains transition metal ion, in the IUPAC naming method, the charge is specified by Roman number. FeCl 2 iron (II) chloride; ferrous chloride FeCl 3 iron (III) chloride; ferric chloride CuCl 2 copper (II) chloride; cupric chloride CuClcopper (I) chloride; cuprous chloride

26. Transition metal ionic compounds –indicate charge on metal with Roman numerals FeCl 2 2 Cl - -2 so Fe is +2 iron(II) chloride FeCl 3 3 Cl - -3 so Fe is +3 iron(III) chloride Cr 2 S 3 3 S -2 -6 so Cr is +3 (6/2)chromium(III) sulfide 2.7

27. –cation: name of element –anion (nonmetal), add “ide” to element name BaCl 2 barium chloride K2OK2O potassium oxide Mg(OH) 2 magnesium hydroxide KNO 3 potassium nitrate 2.7 Naming Ionic Compounds Group 1A (Li, Na etc.), 2A metals (Mg,Ca,etc.), aluminum, zinc have only one type of charge when forming ionic compounds.

28. Worked Example 2.5

29. Naming Molecular compounds common names H 2 O (water), NH 3 (ammonia), CH 4 (methane), H 2 S (hydrogen sulfide) element further left in periodic table is 1 st element closest to bottom of group is 1 st if more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atom (The prefix of “mono” may be omitted for the first element; For oxides, the ending “a” in the prefix may be omitted.) Name first element first and last element ends in ide

30. HIhydrogen iodide NF 3 nitrogen trifluoride SO 2 sulfur dioxide N 2 Cl 4 dinitrogen tetrachloride NO 2 nitrogen dioxide N2ON2Odinitrogen monoxide Molecular Compounds 2.7 (smog, toxic) (laughing gas )

31. 2.7 Steps of naming ionic and binary molecular compounds

32. An acid can be defined as a substance that yields hydrogen ions (H + ) when dissolved in water. HCl Pure substance, hydrogen chloride, gas Dissolved in water (H + Cl - ), hydrochloric acid 2.7 Acids and Bases Anions whose names end in “ide" form acids with “hydro-” prefix and “-ic” ending. When mix acid and water, always add acid into water (exothermic reaction; releasing heat)

33. 2.7

34. An oxoacid (or oxyacid) is an acid that contains hydrogen, oxygen, and another element. HNO 3 nitric acid H 2 CO 3 carbonic acid H 2 SO 4 sulfuric acid 2.7 1.Addition of one O atom to “-ic” acid  ”per…ic”acid HClO 4 perchloric acid 2. Removal of one O atom from “-ic” acid  ”-ous” acid HNO 2 nitrous acid 3. Removal of two O atoms from “-ic” acid  ”hypo…ous” acid HClO hypochlorous acid HClO 3 chloric acid

35. 2.7

37. A base can be defined as a substance that yields hydroxide ions (OH - ) when dissolved in water. When Mix bas and water, always add base into water (exothermic reaction). NaOH sodium hydroxide KOH potassium hydroxide Ba(OH) 2 barium hydroxide 2.7

38. Hydrates are compounds that have a specific number of water molecules attached to them. These waters hold up the crystal structure; when heating, these waters vaporize and the crystal becomes powder. BaCl 2 2H 2 O 2.7 LiClH 2 O MgSO 4 7H 2 O Sr(NO 3 ) 2 4H 2 O barium chloride dihydrate lithium chloride monohydrate magnesium sulfate heptahydrate strontium nitrate tetrahydrate CuSO 4 5H2O CuSO4

39. 2.7