Chapter 2: Atoms, Molecules, and Ions

1. 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

2. 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

3. Chapter 2: Atoms, Molecules, and Ions The Discovery of Atomic Structure R. Millikan (1868-1953): • measured electron charge (oil-drop experiment)

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

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

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

7. 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

8. 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 4 7 9 He Li Be H 2 3 4

9. • 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

10. 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

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

12. 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

13. Chapter 2: Atoms, Molecules, and Ions Average Atomic Mass = Atomic Weight 70amu 30amu 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

14. Chapter 2: Atoms, Molecules, and Ions Average Atomic Mass = Atomic Weight For example:Lithium AW = 6.939 amu 6Li Exact mass: 6.015 amu 7Li Exact mass: 7.016 amu Do the two isotopes exist in equal amounts ? No, because the simple average of the isotope masses is: (6.015 + 7.016) / 2 = 0.5 x 6.015 + 0.5 x 7.016 = 6.516 which is not the correct atomic weight

15. Chapter 2: Atoms, Molecules, and Ions Average Atomic Mass = Atomic Weight For example:Lithium AW = 6.939 amu 6Li Exact mass: 6.015 amu 7Li Exact mass: 7.016 amu Which isotope is more abundant? It must be 7Li because the average mass Is closer to the mass of the 7Li isotope The average is weighted in favor of the more abundant isotope

16. Chapter 2: Atoms, Molecules, and Ions Average Atomic Mass = Atomic Weight For example:Lithium AW = 6.939 amu 6Li Exact mass: 6.015 amu 7Li Exact mass: 7.016 amu What are the fractions of the individual isotopes ? X 6.015 + Y 7.016 = 6.939 X + Y = 1 X 6.015 + (1-X) 7.016 = 6.939 6.015 X + 7.016 – 7.016 X = 6.939 - 1.001 X= - 0.077 X = -0.077/ -1.001 = 0.0769 7.69% 6Li 92.31 % 7Li

17. 1 electron 2 electrons 3 electrons 4 electrons Chapter 2: Atoms, Molecules, and Ions How can you tell how many electrons an element has? number of electrons = number of protons = atomic number 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

18. Chapter 2: Atoms, Molecules, and Ions number of electrons number of protons number of neutrons 16 16 32 – 16 = 16 32S 80Br- 35 + 1 = 36 35 80 – 35 = 45 20 - 2 = 18 20 40 – 20 = 20 40Ca2+

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

20. 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

21. 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

22. Chapter 2: Atoms, Molecules, and Ions Empirical Formulas Molecular Formulas HO H2O2 Hydrogen peroxide C4H10 C2H5 Butane C3H8 C3H8 Propane

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

24. 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

25. Chapter 2: Atoms, Molecules, and Ions How can you tell how many electrons an element will gain/lose? X1 would lose 2 e- to get to the Nb configuration: X12+ X2would gain 3 e- to get to the Nb configuration: X23- NOBLE GASES X3would gain 1 e- to get to the Ne configuration: X3- X4would lose 1 e- to get to the Nc configuration: X4+ Na Nb X2 Nc X1 X4 Nd X3 Ne Nf • Atoms tend to gain/lose the number of electrons needed to achieve the electron configuration of the closest noble gas • Metals tend to form Cations • Nonmetals tend to form Anions

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

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

28. 2+ 2- 6+ 6- 0 0 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 Al3+ O2- Al, O => Na+ O2- Na, O => Na+ Al3+ O2- O2- Na2O Al2O3

29. - 2+ Mg Cl - Cl 1+ 1- 0 2+ 2- 0 Chapter 2: Atoms, Molecules, and Ions Li, Br => Li+ Br- Mg, Cl => LiBr MgCl2

30. - 2+ 1 Cl Mg 2- 2+ Ca O CaO smallest possible ratio! Chapter 2: Atoms, Molecules, and Ions Empirical Formulas for Ionic Compounds: 2- 3+ Al2O3 O Al MgCl2 Ca2O2

31. 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

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

33. 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

34. 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-

35. 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 [ PersulfateSO52-, S2O82- ] Sulfate SO42- Sulfite SO32- Hyposulfite SO22-

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

37. Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds You must know these!

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

39. 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? Memorize e.g. Ammonium

40. Magnesium sulfate Iron(III) chloride Sodium hypochlorite Ammonium hydroxide Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds: chemical formula → name → simple cation: magnesium Mg2+ MgSO4 SO42- → oxyanion: sulfate → transition metal cation: Iron(III) Fe3+ FeCl3 3 Cl- → monoatomic anion: chloride → simple cation: Sodium Na+ NaClO ClO- → oxyanion: hypochlorite → cation: Ammonium NH4+ NH4OH → anion: hydroxide OH-

41. Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds: name → chemical formula Identify the ions Anion Cation Determine charge Determine charge Monoatomic, nonmetal? Transition metal ? Charge is given in Roman numerals Determine charge from Periodic Table (Slide #25) Polyatomic anion? Group 1A, 2A, 3A metal? Determine charge from Periodic Table (Slide #25) Polyatomic cation? Memorize... Hydroxide: OH- Cyanide: CN- Oxyanions! Memorize... Ammonium: NH4+ combine cations & anions so that overall compound is neutral!

42. FeCl2 KCN Na2SO3 Chapter 2: Atoms, Molecules, and Ions Naming Ionic Compounds: name → chemical formula Fe2+ Iron(II) chloride Remember to balance charge! Cl- x 2 More than one polyatomic anion (or cation) => in parantheses! Mg2+ Mg(OH)2 Magnesium hydroxide OH- x 2 K+ Potassium cyanide CN- x 2 Na+ Sodium sulfite SO32-

43. Chapter 2: Atoms, Molecules, and Ions What ions does ClO2 dissociate into? Cl- and 2 O2- Cl- and O22- Cl+ and O2- doesn’t form ions

44. 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!

45. 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 elements 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]

46. Chapter 2: Atoms, Molecules, and Ions Naming Compounds 1) Ionic or molecular? NiO => ionic => Ni2+ and O2- 2 a) Ionic: what are the ions? b) molecular: how many atoms? => Nickel(II) oxide SO => molecular BF3 => molecular => Sulfur monoxide => Boron trifluoride KMnO4 => ionic => K+ and MnO4- => Potassium permanganate

47. Chapter 2: Atoms, Molecules, and Ions Naming Compounds Calcium bromate Ionic or molecular compound? Empirical formula? Ca2+ Ions: BrO3- Ca(BrO3)2 Ionic or molecular compound? SO3 Name? Sulfur trioxide N/A Charge on oxygen? You can only assign “real” charges to ions in ionic compounds You cannot determine the empirical formula of a molecular compound simply by consulting the periodic table SO3 SO SO2