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.

3. Conservation of Mass Antoine Lavoisier (1743–1794): Showed that mass of products is exactly equal to the mass of reactants.

4. The Structure of Atoms01 Cathode-Ray Tube (Thomson, 1856–1940): Cathode rays consist of tiny negatively charged particles, now called electrons.

5. J.J. Thomson, measured mass/charge of e - (1906 Nobel Prize in Physics) e/m =k( 2V/ B 2 r 2 )

6. Mass Spectrometer

7. The Structure of Atoms03 Oil Drop Experiment (Millikan, 1868–1953): Applied a voltage to oppose the downward fall of charged drops and suspend them (1908-1917), Noble Prize:1923 Voltage on plates place 1.602176 x 10 -19 C of charge on each oil drop. Millikan calculated the electron’s mass as 9.109382 x 10 -28 grams.

9. 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 Charge of e - (1923 Nobel Prize in Physics)

11. Discovery of Nucleus (Rutherford, 1871 – 1937): Rutherford irradiated gold foil with a beam of alpha (  ) particles to search for positive charged particles. The Structure of Atoms05

12. (Uranium compound)

13. 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)

14. 1.  particles are scattered equally across a range of deflection angles due to the high density of the foil nuclei. 2.Most  particles pass through the foil without being deflected because most of the volume of the atoms that comprise the foil is empty space. 3.Most  particles are scattered at acute angles as they pass close to the foil nuclei. 4.Most  particles are deflected in a backwards direction from the foil due to the high density of the foil atom nuclei.

15. 1.  particles are scattered equally across a range of deflection angles due to the high density of the foil nuclei. 2.Most  particles pass through the foil without being deflected because most of the volume of the atoms that comprise the foil is empty space. 3.Most  particles are scattered at acute angles as they pass close to the foil nuclei. 4.Most  particles are deflected in a backwards direction from the foil due to the high density of the foil atom nuclei.

16. 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

17. 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

18. Atomic Mass Atomic and molecular masses can be measured with great accuracy with a mass spectrometer. Z/m = 2V/ B 2 r 2 V is the voltage between cathode and anode and r is the mean radius of the circular electron orbit, both of which can be measured, and B is the magnetic field through which the electrons pass.

19. Subatomic Particles (Table 2.1) mass p = mass n = 1840 x mass e -

20. 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

21. Protium DeuteriumTritium

22. How many protons, neutrons, and electrons are in C 14 6 ? How many protons, neutrons, and electrons are in C 11 6 ? 6 protons, 8 (14 - 6) neutrons, 6 electrons 6 protons, 5 (11 - 6) neutrons, 6 electrons Do You Understand Isotopes?

23. How many neutrons are there in an atom of 14 C? 1.6 2.8 3.12 4.14

24. Correct Answer: Atomic number Mass number 14 6 C The difference between the mass number and the atomic number is the number of neutrons (14  6) = 8. 1.6 2.8 3.12 4.14

25. 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

26. Diatomic Gases These seven elements occur naturally as molecules containing two atoms.

27. 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

28. 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 -

29. 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+3+ How many protons and electrons are in Se 78 34 2- ?

30. 2.5 Ionic Charges

31. 2.6

32. ionic compounds consist of a combination of cations and an anions 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

33. Writing Formulas Because compounds are electrically neutral, one can determine the formula of a compound this way: –The charge on the cation becomes the subscript on the anion. –The charge on the anion becomes the subscript on the cation. –If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor.

34. 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 2 x +1 = +21 x -2 = -2 Na + CO 3 2-

35. Some Polyatomic Ions 2.7

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

37. 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

38. Molecular compounds –nonmetals or, nonmetals + metalloids –common names H 2 O, CH 4, –element further left in periodic table is, usually, 1 st –element closest to bottom of group is, usually, 1 st if 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 ide 2.7

39. 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