1. Atoms, Molecules and Ions Chapter 2

2. Dalton’s Atomic Theory (1808) 1. Elements are composed of extremely small particles called atoms. 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. 2. Compounds are composed of atoms of more than one element. The relative number of atoms of each element in a given compound is always the same. 3. Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions. 2.1

3. 2

4. 8 X 2 Y 16 X8 Y + 2.1

5. J.J. Thomson, measured mass/charge of e - (1906 Nobel Prize in Physics) 2.2

6. Cathode Ray Tube 2.2

7. e - charge = -1.60 x 10 -19 C Thomson’s charge/mass of e - = -1.76 x 10 8 C/g e - mass = 9.10 x 10 -28 g Measured mass of e - (1923 Nobel Prize in Physics) 2.2

8. Everybody Has Avogadro’s Number! But Where Did it Come From? It was NOT just picked! It was MEASURED. It was NOT just picked! It was MEASURED. One of the better methods of measuring this number was the Millikan Oil Drop Experiment One of the better methods of measuring this number was the Millikan Oil Drop Experiment Since then we have found even better ways of measuring using x- ray technology Since then we have found even better ways of measuring using x- ray technology

9. (Uranium compound) 2.2

11. The modern view of the atom was developed by Ernest Rutherford (1871-1937).

12. 1.atoms positive charge is concentrated in the nucleus 2.proton (p) has opposite (+) charge of electron (-) 3.mass of p is 1840 x mass of e - (1.67 x 10 -24 g)  particle velocity ~ 1.4 x 10 7 m/s (~5% speed of light) (1908 Nobel Prize in Chemistry) 2.2

13. 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 “If the atom is the Houston Astrodome, then the nucleus is a marble on the 50-yard line.”

14. Chadwick’s Experiment (1932) H atoms - 1 p; He atoms - 2 p mass He/mass H should = 2 measured mass He/mass H = 4  + 9 Be 1 n + 12 C + energy neutron (n) is neutral (charge = 0) n mass ~ p mass = 1.67 x 10 -24 g 2.2

15. mass p = mass n = 1840 x mass e - 2.2

16. Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei X A Z H 1 1 H (D) 2 1 H (T) 3 1 U 235 92 U 238 92 Mass Number Atomic Number Element Symbol 2.3

18. 6 protons, 8 (14 - 6) neutrons, 6 electrons 6 protons, 5 (11 - 6) neutrons, 6 electrons Do You Understand 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 ?

19. Period Group Alkali Metal Noble Gas Halogen Alkali Earth Metal 2.4

20. Chemistry In Action Natural abundance of elements in Earth’s crust Natural abundance of elements in human body 2.4

21. A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds 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

22. ELEMENTS THAT EXIST AS DIATOMIC MOLECULES Remember: BrINClHOF These elements only exist as PAIRS. Note that when they combine to make compounds, they are no longer elements so they are no longer in pairs!

23. An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge 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. Na 11 protons 11 electrons Na + 11 protons 10 electrons Cl 17 protons 17 electrons Cl - 17 protons 18 electrons 2.5

24. Forming Cations & Anions A CATION forms when an atom loses one or more electrons. An ANION forms when an atom gains one or more electrons Mg --> Mg 2+ + 2 e- F + e- --> F -

25. A monatomic ion contains only one atom A polyatomic ion contains more than one atom 2.5 Na +, Cl -, Ca 2+, O 2-, Al 3+, N 3- OH -, CN -, NH 4 +, NO 3 -

26. 13 protons, 10 (13 – 3) electrons 34 protons, 36 (34 + 2) electrons Do You Understand Ions? 2.5 How many protons and electrons are in ?Al 27 13 3+ How many protons and electrons are in ?Al 78 34 2-

27. 2.5

28. 2.6

29. 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

30. ionic compounds consist of a combination of cation(s) and an anion(s) the formula is always the same as the empirical formula the sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero The ionic compound NaCl 2.6

31. Formula of Ionic Compounds Al 2 O 3 2.6 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-

32. 2.6

33. 2.7

34. Examples of Older Names of Cations formed from Transition Metals (memorize these!!) From Zumdahl

35. Chemical Nomenclature Ionic Compounds Ionic Compounds often a metal + nonmetaloften a metal + nonmetal anion (nonmetal), add “ide” to element nameanion (nonmetal), add “ide” to element name BaCl 2 barium chloride K2OK2O potassium oxide Mg(OH) 2 magnesium hydroxide KNO 3 potassium nitrate 2.7

36. Transition metal ionic compounds Transition metal ionic compounds indicate charge on metal with Roman numeralsindicate 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

37. Molecular compounds Molecular compounds nonmetals or nonmetals + metalloidsnonmetals or nonmetals + metalloids common namescommon names H 2 O, NH 3, CH 4, C 60 H 2 O, NH 3, CH 4, C 60 element further left in periodic table is 1 stelement further left in periodic table is 1 st element closest to bottom of group is 1 stelement 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 atomif more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atom last element ends in idelast element ends in ide 2.7

38. 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 TOXIC ! Laughing Gas

39. 2.7

40. An acid can be defined as a substance that yields hydrogen ions (H + ) when dissolved in water. HCl Pure substance, hydrogen chloride Dissolved in water (H + Cl - ), hydrochloric acid An oxoacid 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 HNO 3

41. 2.7

44. A base can be defined as a substance that yields hydroxide ions (OH - ) when dissolved in water. NaOH sodium hydroxide KOH potassium hydroxide Ba(OH) 2 barium hydroxide 2.7

46. Mixed Practice 1. Dinitrogen monoxide 2. Potassium sulfide 3. Copper (II) nitrate 4. Dichlorine heptoxide 5. Chromium (III) sulfate 6. Ferric sulfite 7. Calcium oxide 8. Barium carbonate 9. Iodine monochloride 1.N 2 O 2.K 2 S 3.Cu(NO 3 ) 2 4.Cl 2 O 7 5.Cr 2 (SO 4 ) 3 6.Fe 2 (SO 3 ) 3 7.CaO 8.BaCO 3 9.ICl

47. Mixed Practice 1. BaI 2 2. P 4 S 3 3. Ca(OH) 2 4. FeCO 3 5. Na 2 Cr 2 O 7 6. I 2 O 5 7. Cu(ClO 4 ) 2 8. CS 2 9. B 2 Cl 4 1.Barium iodide 2.Tetraphosphorus trisulfide 3.Calcium hydroxide 4.Iron (II) carbonate 5.Sodium dichromate 6.Diiodine pentoxide 7.Cupric perchlorate 8.Carbon disulfide 9.Diboron tetrachloride