Atomic Structure. Ch 3 Prentice Hall

Transcription

1 Atomic Structure Ch 3 Prentice Hall

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3 The Nuclear Atom By 1919 Rutherford concluded that the atom has a dense positive center called the nucleus containing what he called protons The electrons surround the nucleus within the electron cloud (Draw this model)

4 The Nuclear Model Particle Relative Mass Relative Charge Location In Atom Electron 0 (Basically has no mass) 1- Electron Cloud (Atomic #) Proton (I.D.) 1 (amu) 1+ Nucleus (Atomic #) Neutron 1 (amu) 0 (neutral) Nucleus (Mass-# = n 0 )

5 You should be able to write and interpret symbols

6 You should be able to write and interpret symbols

7 Use your periodic table Co (Cobalt): A Z Co A = and Z = mass number (A) atomic number (Z) number of protons number of neutrons number of electrons

8 59 27 Co Use your periodic table Co (Cobalt): 59 = mass number (A) 27 = atomic number (Z) 27 = number of protons 32 = number of neutrons 27 = number of electrons

9 How many protons and electrons are present in a carbon atom?

10 What is the name of the element that has atoms that contain 82 protons?

11 Write the chemical symbol for the ion with 33 protons and 36 electrons. What is an ion? It is an atom with a charge

12 Write the chemical symbol for the ion with 12 protons and 10 electrons.

13 Write the chemical symbol for the ion with 17 protons and 18 electrons.

14 How many protons, neutrons, and electrons are present in the Se 2- ion?

15 Write the complete chemical symbol for the ion with 31 protons, 39 neutrons, and 28 electrons.

16 Isotopes

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20 Elements naturally come in a variety of isotopes These atoms differ in the number of neutrons Same number of protons (the same element) The average atomic mass (amu) is the weighted average of all the isotopes of an element. A mass spectrometer is an instrument used to measure the composition of compounds and mass of elements

21 Example: A sample of cesium is 75% 133 Cs, 20% 132 Cs and 5% 134 Cs. What is the average atomic mass? Answer:.75 x 133 = x 132 = x 134 = Total = amu *Know how to do the opposite, AP like this format

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23 Combustion Formula of a Compound

24 The AP Exam will most likely give you a combination of work to complete by using a combustion device which analyzes substances containing C and H. It is burned in excess O 2 producing CO 2 and H 2 O, these products are then collected and from here one can determine the %C in CO 2 and %H in H 2 O

25 g of a compound is reacted with O 2 & g of CO 2 & g of H 2 O is collected. The unknown compound has C, H and N, what s the empirical & molecular formula molar mass = g/mol? Go in the order of C, H, O, (N) Remember %C in CO 2 (part/whole x 100% = % comp.): %C: g C x g CO 2 = g C g CO 2 % H: g H 2 x g H 2 O = g of H g H 2 O g compound = g C g H + g N = g N

26 gC x 1mol g H x 1mol g N x 1mol g 1.01 g g = mol C = mol H = mol N Divide by Smallest number of moles = mol 1 C : 5 H : 1 N CH 5 N empirical amu = True (given) amu = /31.07 = 1 (CH 5 N ) = CH 5 N is true formula

27 Periodic Trends

28 Niels Bohr s Planetary Model The Planetary model is based upon the orbits of our solar system Not a 100% correct model Can only be used for elements 1-20 But good enough to explain some concepts

29 Electrons are found in orbits 8 The first orbital holds a max of 2 e- The second and third orbital each holds a max of 8 e-

30 Valence Electrons 8 The outer electrons are called the valence electrons, they are the electrons that do chemistry

31 Copy trends on your blank periodic table.

32 Copy trends on your blank periodic table.

33 Family/Group Names

34 Groups/Families Elements with similar chemical and physical properties are in the same column Columns are called groups or families

35 Why do elements in the same group/family react similarly?

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37 Matter reacts because of the outermost orbit electrons--they are called valence electrons Octet Rule: Atoms become stable when they obtain 8 valence electrons When they gain or lose electrons they react Duet Rule: Exceptions to the Octet Rule hydrogen and helium--they are so tiny that they are stable with only 2 valence electrons

38 Notice This Trend

39 Let s Learn The Group Names

40 The Alkali Metals Group I

41 The Alkaline Earth Metals Group II

42 The Boron Family Group III

43 The Carbon Family Group IV

44 The Nitrogen Family Group V

45 The Oxygen Family Group VI

46 The Halogens Group VII

47 What is the periodic trend for the states of: Chlorine, Bromine, Iodine Cl 2 Br 2 I 2

48 The Noble Gases Are Group VIII

49 The Transition Metals

50 The Inner Transition Metals The Lanthanides The Actinides

51 Rows are called periods Each period shows the pattern of properties repeated in the next period Period 1 Period 2 Period 3 Period 4 Period 5 Period 6 Period 7

52 Metals, Metalloids, Nonmetals

53 Metallic Character Metals Malleable & ductile Shiny, lustrous Good conductors of heat and electricity Bonding Metal + nonmetal = ionic Metalloids (Semi- metals) Also known as semi-metals Show some metal and some nonmetal properties Nonmetals Brittle in solid state Poor conductors of heat and electricity (insulators) Bonding Nonmetal + Nonmetal = molecular

54 Electron Configurations Ch 4

55 Example - Hydrogen Period # # of orbits 1s 1 Valence e- Group # Shape of orbit Courtesy Christy Johannesson

56 Electrons arrange themselves in orbitals called electron configurations, note your periodic table When you fill the electrons in their orbitals you need to follow these rules : 1. Begin filling the electrons within the lowest energy orbital 2. Fill the electrons one at a time and then pair up the electrons 3. When you pair the electrons, pair them up with opposite spins 4. Fill the electrons according to the following pattern

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60 Aufbau Principle Aufbau is German for building up. Add e- to the lowest energy orbital (1s)

61 Pauli Exclusion Principle Each orbital holds 2 e- of opposite spins

62 Opposite Spins

63 Hund s Rule One e- in each separate orbital with parallel spins before pairing e-.

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65 Orbital Shapes and Energies

66 s Orbitals Spherical shape s orbitals become larger as the value of n increases Nodes are areas of zero probability

67 p Orbitals Peanut shaped (having two lobes) Are labeled n px, n py, n pz according to the axis at which the lobe lies

68 d Orbitals Daisy shaped (two p orbitals) Note the axis at which each lobe lies

69 f Orbitals Fancy shaped (highly complex shape) Not involved in bonding in most compounds

70 Actual Pictures of Shapes of Electron Clouds s orbital = spherical shape p orbital = peanut shape d orbital = daisy shape f orbital = fancy shape

71 Memorize!

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73 Shorthand Notation of e- Configurations

74 To save space, chemists often use abbreviated electron configurations.

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76 Know about isoelectronic species

77 3.10 Ions

78 The loss or gain of electrons creates an ion a charged atom This occurs to create a more stable atom Ion Formulas: a. Ca 2+ b. Clc. Na+ d. S 2- e. Ca 2+ f. P 3-

79 Electrolytes are ionic substances that are either dissolved in water or melted. The free ions carry a current and conduct electricity

80 Memorize Charges & Group Names For Exam

81 Metals tend to lose electrons Will be (+) in charge (due to losing negatives) Positive ions are called cations

82 Nonmetals tend to gain electrons Will be (-) in charge (due to gaining negatives) Negative ions are called anions

83 Together cations and anions have a net charge of zero

84 Ions of opposite charge are attracted to each other to form an ionic compound ionic compounds form a crystal lattice

85 Let s watch how metals transfer electrons to a nonmetal

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88 Writing Simple Formulas What Is A Formula?

89 Formula Rules 1. Write the metal first and then the nonmetal second. 2. Find the charges for each ion (use your periodic table) 3. Criss-Cross 4. If possible reduce charges 5. The overall charge must be zero!! 6. Name the ionic compound. 7. Take the metal name and change the nonmetal to -ide. a. Ca 2+ and Clb. Na+ and S 2- c. Ca 2+ and O 2- d. Pb 4+ and O 2-

90 Ca 2+ and Cl- Ca 2+ has a 2+ charge, so two Cl- ions will be needed. Ca 2+ + Cl- Cl- The formula is CaCl 2 Notice: since we only need one Ca we DO NOT USE the subscript of 1 (Ca 1 Cl 2 )

91 You Do Ca 2+ and O 2-

92 Ca 2+ and NO 3 - In this case we need parenthesis to produce a zero net charge. Ca 2+ + NO 3 - NO 3 - The formula is Ca(NO 3 ) 2

93 Now Go Back And Name Them

94 You need to memorize the polyatomic ions!!!!

95 Other Periodic Trends Ch 11.11

96 Periodic Trends If you remember, many properties of the elements change in a predictable way as you move through the periodic table when the elements are arranged by increasing atomic number. These systematic variations are called periodic trends and follow the periodic law.

97 The atomic size is measured from the center of the nucleus to the outermost electron, this is known as atomic radius It is usually measured in nanometers (1x10-9 m), picometers (1x10-12 m), angstroms (1x10-10 m) Note the trend for atomic radius in your periodic table Note your periodic table. What is the periodic trend for radii as you move from left to right and top--down?

98 Moving down a group: Atoms get bigger b/c there is a greater number of electrons, so the cloud gets bigger. The quantum number (n) increases from top to bottom. This is due to electronelectron repulsion (shielding)

99 Moving across a period: Atoms get smaller b/c there is a greater number of protons that pull in the electrons, making the atom smaller. This is called nuclearelectron attraction. Note that the quantum number (n) stays the same.

100 Internal Atomic Energies 1. Kinetic energy of moving electrons 2. Potential energy of attraction between nucleus and electrons--nuclear electron attraction 1. Also known as effective nuclear charge Z eff 3. Potential energy of repulsion between electrons--electron-electron repulsion 1. Also known as shielding

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102 The movie will show how nuclear-electron attraction effects the atom

103 This movie will review if there is a great nuclearelectron attraction then this causes a high electron affinity (a BIG negative number)

104 Note how the transition metals do not follow this trend. This is because the outer shell, for example, contains 4s electrons, but electrons are being added to the 3d orbitals across the series. The effect of getting small, moving left to right, is cancelled out by increased electron-electron repulsion, causing the size to increase.

105 Periodic Trends For Cations What is the periodic trend for atomic radii for cations?

106 Note The Trend

107 Periodic Trends For Anions What is the periodic trend for atomic radii for anions?

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109 Ionization Energy

110 How and why do atoms lose electrons? Atoms have a tendency to lose electrons due to ionization energy Metals tend to be more stable when they lose electrons--to obtain an octet or a duet General Equation: X X + + 1e-

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112 The ionization energy is the energy required to remove an electron from an atom or ion Note your table of elements. What is the trend for ionization energy?

113 Ionization Energy What is the charge of Al? Why the large jump in energy needed to remove the 4th electron?

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115 How Do Ions Form?

116 Metals and Nonmetal Charges Metals tend to lose electrons (low ionization energy) Easier to remove electrons Nonmetals tend to gain electrons (high ionization energy) More difficult to remove electrons

117 Ions that lose electrons are called cations (positively (+) charged ions)

118 Ions that gain electrons are called anions (negatively charged ion)

119 Electron Affinity

120 The electron affinity is the energy required to add an electron to an atom General Equation: X + 1e- X -

121 What is the periodic trend for electron affinity?

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123 Metals and Nonmetal Charges Metals tend to lose electrons (low electron affinity--low affinity for electrons) Nonmetals tend to gain electrons (high electron affinity--high affinity for electrons)

124 Let s Review Metals tend to lose e- Low ionization energy --the less energy is needed to remove electrons Low electron affinity electron affinity because they do not want to acquire electrons Nonmetals tend to gain e- High ionization energy --the more energy needed to remove electrons High electron affinity because they acquire electrons

125 Let s Review