Chapter 2: Atoms, Molecules, and Ions

1. Chapter 2: Atoms, Molecules, and Ions The Atomic Theory of Matter Democritus (460-371 BC): • matter consists of atoms which are solid particles (a-tomos = un-cuttable) • Democritus' ideas were ignored for the next 2000 years

2. Chapter 2: Atoms, Molecules, and Ions The Atomic Theory of Matter John Dalton (1766-1844): •Elements are made of tiny particles called atoms • all atoms of one element are identical • atoms are not created nor destroyed in chemical processes • atoms of different elements can combine to form compounds

3. Chapter 2: Atoms, Molecules, and Ions The Atomic Theory of Matter Dalton’s Atomic Theory explained.. … The Law of Constant Composition [in one compound, number and kind of atoms is constant] … The Law of Conservation of Mass [total mass before reaction = total mass after reaction] … The Law of Multiple Proportions [If two elements form more than one compound, the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers]

4. Chapter 2: Atoms, Molecules, and Ions HW: 8 The Atomic Theory of Matter The Law of Multiple Proportions: 12 g carbon + 16 g oxygen => CO 12 g carbon + 32 g oxygen => CO2 32 g : 16 g = 2 : 1

5. Chapter 2: Atoms, Molecules, and Ions The Discovery of Atomic Structure J.J. Thomson (1856-1940): • discovered the electron • atoms of all elements contain electrons • electron: negatively charged particles of very small mass

6. Chapter 2: Atoms, Molecules, and Ions The Discovery of Atomic Structure _ Cathode Ray Tube + e- HV Determination of charge to mass ratio: e-

7. Chapter 2: Atoms, Molecules, and Ions The Discovery of Atomic Structure J.J Thomson's original Cathode Ray Tube

8. - Chapter 2: Atoms, Molecules, and Ions HW: 14a,b The Discovery of Atomic Structure R. Millikan (1868-1953): • measured electron charge

9. Rutherford's Model: J.J. Thomson's Model: “Plum Pudding Model” + "smeared-out" positive charge Chapter 2: Atoms, Molecules, and Ions The Discovery of Atomic Structure Electrons are negatively chargedbut atoms as a whole are neutral.

10. Chapter 2: Atoms, Molecules, and Ions The Discovery of Atomic Structure

11. + Chapter 2: Atoms, Molecules, and Ions The Discovery of Atomic Structure Rutherford's Model:

12. Chapter 2: Atoms, Molecules, and Ions The Discovery of Atomic Structure Ernest Rutherford (1871-1937): • Rutherford concluded that (a) the atom has a positive charge concentrated in the nucleus (b) the electrons orbit around the positive nucleus (c) that the atom is mostly empty space

13. Chapter 2: Atoms, Molecules, and Ions HW: 12 The Discovery of Atomic Structure More evidence for atomic substructure: • some substances spontaneously break down into smaller particles (radioactivity) • a-particles (heavy, +2 charge) • b-particles (small mass, -1 charge) • g-rays (electromagnetic radiation => no mass, no charge)

14. PROTONS: positively charged (+1) NEUTRONS: no charge Chapter 2: Atoms, Molecules, and Ions The Modern View of Atomic Structure The nucleus is structured:

15. Chapter 2: Atoms, Molecules, and Ions The Modern View of Atomic Structure The mass of an atom is concentrated in its nucleus: MASS Charge •proton: 1 atomic mass unit (1amu) +1 •neutron: 1 amu 0 •electron: negligible mass -1 (5.486 x 10-4 amu) (1.6 x 10-19C) 1 amu = 1.66054 x 10-24 g

16. 1 1 themass number counts protons and neutrons the atomic number counts the number of protons Chapter 2: Atoms, Molecules, and Ions The Modern View of Atomic Structure Elements differ in their number of protons: Hydrogen: 1 proton Helium: 2 protons 2 neutrons Lithium: 3 protons 4 neutrons Beryllium: 4 protons 5 neutrons He Li Be H

17. • atoms of one element can exist in different 'versions' : all atoms must still have the same number of protons but they may have a different number of neutrons Chapter 2: Atoms, Molecules, and Ions The Modern View of Atomic Structure How about the neutrons? • an element is defined by the number of protons

18. 1 H 1 Chapter 2: Atoms, Molecules, and Ions The Modern View of Atomic Structure Isotopes of an element: same number of protons but different number of neutrons 3 2 H H 1 1 Hydrogen or Protium Deuterium Tritium

19. Chapter 2: Atoms, Molecules, and Ions Average Atomic Mass = Atomic Weight Average Mass = fraction of heavy x mass of heavy + fraction of light x mass of light = 3/4 x 70amu + 1/4 x 30amu = 0.75 x 70amu + 0.25 x 30amu = 60amu 75% 25%

20. Chapter 2: Atoms, Molecules, and Ions HW: 33a Average Atomic Mass = Atomic Weight Si naturally occurs in three isotopes: 92.2% of 28Si (27.98 amu) 4.7% of 29Si (28.98 amu) 3.1% of 30Si (29.97 amu) what is the atomic weight of Si?

21. Atomic Number Chapter 2: Atoms, Molecules, and Ions Periodic Table • Elements are sorted according to atomic number 6 C 12.01 Atomic weight

22. Chapter 2: Atoms, Molecules, and Ions HW: 23 How can you tell how many electrons an element has? Hydrogen: 1 proton Helium: 2 protons 2 neutrons Lithium: 3 protons 4 neutrons Beryllium: 4 protons 5 neutrons 4 7 9 1 He Li Be H 2 3 4 1

23. Chapter 2: Atoms, Molecules, and Ions Periodic Table • Elements with similar properties fall in vertical groups • A row in the periodic table is called a period

24. Noble Gases Alkaline Earth Metals Transition metals Alkali Metals Halogens Chapter 2: Atoms, Molecules, and Ions HW: 37 Periodic Table • Most elements are metals VIII A I A II A III A IV A VA VI A VIIA

25. Chapter 2: Atoms, Molecules, and Ions Molecules and Molecular Compounds • Some elements exist as diatomic molecules at room temp. • H2 N2 O2 F2 Cl2 Br2 I2

26. Chapter 2: Atoms, Molecules, and Ions Molecules and Molecular Compounds The periodic table helps predict how elements combine Empirical Formulas Molecular Formulas • Only gives relative number • of atoms in compound • Show actual number and • types of atoms in a molecule • Subscripts are smallest • whole-number ratios

27. Chapter 2: Atoms, Molecules, and Ions Empirical Formulas Molecular Formulas H2O2 Hydrogen peroxide C4H10 Butane C3H8 Propane

28. Space-filling model Perspective drawing Ball-and-Stick model Chapter 2: Atoms, Molecules, and Ions HW: 45 Drawing Molecules: methane Structural formula

29. Ions are formed when a neutral atom - gains electrons or - loses electrons e- + Li Li Cation - e- Anion Br Br Chapter 2: Atoms, Molecules, and Ions Ions and Ionic Compounds

30. Noble Gases Alkaline Earth Metals Alkali Metals Halogens Chapter 2: Atoms, Molecules, and Ions Which Elements form Anions, which Cations? • Metalstend to form Cations • Nonmetalstend to form Anions VIII A I A II A III A IV A VA VI A VIIA

31. Chapter 2: Atoms, Molecules, and Ions HW: 49,50 How can you tell how many electrons an element will gain/lose? NOBLE GASES Na Nb X2 Nc X1 X4 Nd X3 Ne Nf • Metals tend to form Cations • Nonmetals tend to form Anions • Atoms tend to gain/lose the number of electrons needed • to achieve the electron configuration of the closest noble gas

32. Chapter 2: Atoms, Molecules, and Ions Cations and Anions can combine to from Ionic Compounds + Li Li Cation e- - Anion Br Br

33. Chapter 2: Atoms, Molecules, and Ions Cations and Anions can combine to from Ionic Compounds Ionic Crystal – not a discrete molecule

34. Chapter 2: Atoms, Molecules, and Ions Empirical Formulas for Ionic Compounds: (A) determine charge of ions formed (B) add ions so that compound is neutral overall Al, O => Na, O => Na2O Al2O3

35. Chapter 2: Atoms, Molecules, and Ions HW: 51,53 Li, Br => Mg, Cl => LiBr MgCl2

36. - 2+ 1 Cl Mg 2- 2+ Ca O Chapter 2: Atoms, Molecules, and Ions Empirical Formulas for Ionic Compounds: 2- 3+ Al2O3 O Al MgCl2 CaO

37. Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds: cations come first • (Ia) Monoatomic Cations: • Metal cations keep the name of the element: • Na+ sodium ion Li+ Lithium ion Zn2+ Zinc ion • If a metal can form different kinds of cations (transition metals), • the charge is indicated by a Roman Numeral: • Fe2+ Iron(II) ion • Fe3+ Iron(III) ion • Co2+Cobalt(II) ion

38. Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds • (Ib) Cations formed from Nonmetals: • end in-ium: • NH4+ ammonium ion H3O+ Hydronium ion

39. OH- Hydroxide ion CN- Cyanide ion Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds • (IIa) Monoatomic and Simple Polyatomic Anions • Are derived from the element name by replacing the ending with -ide N3- Nitride ion O2- Oxide ion

40. Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds • (IIb) Oxyanions (polyatomic anions containing oxygen) • The most common oxyanion of an element ends in -ate • One more oxygen: per-.....-ate • One fewer oxygen:-ite • Two fewer oxygen:hypo-.....-ite Perchlorate ClO4- Chlorate ClO3- Chlorite ClO2- Hypochlorite ClO-

41. Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds • (IIb) Oxyanions (polyatomic anions containing oxygen) • The most common oxyanion of an element ends in -ate • One more oxygen: per-.....-ate • One fewer oxygen:-ite • Two fewer oxygen:hypo-.....-ite [ Persulfate SO52-, S2O82- ] Sulfate SO42- Sulfite SO32- Hyposulfite SO22-

42. Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds Common Oxyanions: Carbonate CO32- Nitrate NO3- Phosphate PO43- Sulfate SO42- Chlorate ClO3- Bromate BrO3- Iodate IO3-

43. Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds

44. Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds HCO3- Hydrogen carbonate ion or Bicarbonate ion You must know these!

45. Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds: chemical formula → name Identify the ions Cation Anion monoatomic or simple polyatomic anion? Group 1A, 2A, 3A metal? oxyanion? Transition metal ? Element name per ... ate ... ate ... ite hypo ... ite -ide Element name and charge in Roman numerals Nonmetal ion? e.g. Ammonium

46. Chapter 2: Atoms, Molecules, and Ions HW: 60,96 Naming Ionic Compounds: chemical formula → name MgSO4 FeCl3 NaClO NH4OH

47. Chapter 2: Atoms, Molecules, and Ions HW: 61 Naming Ionic Compounds: name → chemical formula Fe(II) chloride Magnesium hydroxide Potassium cyanide Sodium sulfite

48. Chapter 2: Atoms, Molecules, and Ions Naming Molecular Compounds does not dissociate into ions! ClO2 Metalcations + Nonmetal anions => ionic compounds Nonmetal cations + Nonmetal anions => ionic compounds (e.g. NH4+) Nonmetal+ Nonmetal => molecular compounds Before you start naming, determine what kind of compound you have!

49. Chapter 2: Atoms, Molecules, and Ions Naming Binary Molecular Compounds ClO2 Chlorine dioxide • Name of the element farther to the left in the P.T. comes first - except oxygen, which is usually named last • If both element are from the same group, the heavier one is named first • The second element is given an -ideending • Greek prefixes indicate number of atoms of each element involved [mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona- , deca-] [mono-prefix isnever used with 1st element]

50. Chapter 2: Atoms, Molecules, and Ions Naming Compounds 1) Ionic or molecular? NiO 2 a) Ionic: what are the ions? b) molecular: how many atoms? SO BF3 KMnO4