John Dalton MSU Gallery of Chemists' Photo-Portraits and Mini- Biographies

Transcription

1 Atoms and Elements

2 John Dalton Dalton developed the atomic theory of matter as a consequence of his researches on the behaviour of gases. He developed the laws of definite and multiple proportions. A complete scientist, Dalton also made important observations on the aurora borealis, rain, trade winds, and color blindness. The atomic mass unit, the Dalton, is named for him. MSU Gallery of Chemists' Photo-Portraits and Mini- Biographies

3 Scanning Tunneling Microscope 1986 Nobel Prize

4 Operation of a STM

5 Superconducting YBa2Cu3O7

6 Early Philosophy of Matter ultimate, tiny, indivisible particle Leucippus and Democritus infinitely divisible Plato and Aristotle best debater was the person assumed correct, i.e., Aristotle

7 Scientific Revolution late 16 th century, the scientific approach to understanding nature next 150+ years, observations about nature were made that could not easily be explained Aristotelian approach

8 Law of Conservation of Mass total m reactants = total m of products Antoine Lavoisier

9 Reaction of Sodium with Chlorine to Make Sodium Chloride 7.7 g Na g Cl g NaCl

10 LAW OF DEFINITE PROPORTIONS All samples of a given compound, regardless of their source or how they were prepared, have the Joseph Proust

11 Proportions in Sodium Chloride a g sample of sodium chloride contains 39.3 g of sodium and 60.7 g of chlorine mass of mass of Cl Na 60.7 g 39.3 g 1.54 a g sample of sodium chloride contains 78.6 g of sodium and g of chlorine mass of mass of Cl Na g 78.6 g 1.54 a g sample of sodium chloride contains g of sodium and g of chlorine mass of mass of Cl Na g g 1.541

12 LAW OF MULTIPLE PROPORTIONS When two elements A and B form two different compounds, the masses of B that combine with 1 g of A can be expressed as a John Dalton

13 Oxides of Carbon carbon monoxide contains 1.33 g of oxygen for every 1.00 g of carbon carbon dioxide contains 2.67 g of oxygen for every 1.00 g of carbon since there are twice as many oxygen atoms per carbon atom in carbon dioxide than in carbon monoxide, the oxygen mass ratio should be 2 mass of oxygen that combines with 1g of carbon in carbon dioxide mass of oxygen that combines with 1g of carbon in carbon monoxide 2.67 g 1.33g 2

14 DALTON S ATOMIC THEORY 1) Each element is composed of tiny, indestructible particles called atoms still correct? 2) All atoms of a given element has the same mass and other properties that distinguish them from atoms of other elements still correct? 3) Atoms combine in simple, whole-number ratios to form molecules of compounds 4) In a chemical reaction, atoms of one element cannot change into atoms of another element they simply rearrange the way they are attached

15 Some Notes on Charge

16 Cathode Ray Tubes cathode anode

17 J.J. THOMSON cathode ray was composed of tiny particles with an electrical charge measured the amount of it takes to deflect their path a given amount

18 Thomson s Experiment

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20 THOMSON S RESULTS the cathode rays are made of tiny particles these particles have a charge because the beam always deflected toward the + plate the amount of deflection was related to two factors and every material tested contained these same particles the charge/mass of these particles was x 10 8 C/g the charge/mass of the hydrogen ion is x 10 4 C/g

21 THOMSON S CONCLUSIONS if the particle has the same amount of charge as a hydrogen ion, then it must have a mass almost 2000x smaller than hydrogen atoms! later experiments by Millikan showed that the particle did have the same amount of charge as the hydrogen ion the only way for this to be true is if these particles were pieces of atoms apparently, the atom is not unbreakable Thomson believed that these particles were therefore the ultimate building blocks of matter these cathode ray particles became known as

22 Millikan s Oil Drop Experiment

23 Electrons electrons are particles found in all atoms cathode rays are streams of electrons the electron has a charge of x C the electron has a mass of 9.1 x g

24 A New Theory of the Atom Thomson s Plum Pudding Atom or maybe a raisins in oatmeal model

25 Predictions of the Plum Pudding Atom the mass of the atom is due to the mass of the electrons within it electrons are the only particles in Plum Pudding atoms the atom is mostly empty space cannot have a bunch of negatively charged particles near each other as they would repel

26 RADIOACTIVITY in the late 1800s, Henri Becquerel and Marie Curie certain elements emit small, energetic particles or rays these energetic particles could penetrate matter Ernest Rutherford discovered that there were three different kinds of emissions particles with a mass 4x H atom and + charge particles with a mass ~1/2000 th H atom and charge that are energy rays, not particles

27 Rutherford s Experiment How can you prove something is empty?

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29 Rutherford s Experiment Radioactive Sample Alpha Particles Striking Screen Lead Box Gold Foil Fluorescent Screen

30 Rutherford s Results Over 98% of the particles went straight through About 2% of the particles went through but were deflected by large angles About 0.01% of the particles bounced off the gold foil...as if you fired a 15 cannon shell at a piece of tissue paper and it came back and hit you.

31 RUTHERFORD S CONCLUSIONS Atom mostly because almost all the particles went straight through Atom contains a dense that was small in volume compared to the atom but large in mass because This dense particle was charged because of the large of some of the particles

32 a few of the particles do not go through Plum Pudding Atom Nuclear Atom... if atom was like a plum pudding, all the particles should go straight through most particles go straight through some particles go through, but are deflected

33 RUTHERFORD S INTERPRETATION THE NUCLEAR MODEL 1) The atom contains a tiny dense center called the the amount of space taken by the is only about 1/10 trillionth the volume of the atom 2) The has essentially the entire of the atom the weigh so little they give practically no mass to the atom 3) The is charged the amount of positive charge balances the negative charge of the electrons 4) The electrons are dispersed in the empty space of the atom surrounding the nucleus

34 STRUCTURE OF THE ATOM same amount of charge as an electron but opposite sign based on measurements of the nuclear charge of the elements protons charge = x C mass = x g For an atom to be neutral there must be equal

35 Relative Mass and Charge we generally talk about the mass of atoms by comparing it to 1/12 th the mass of a carbon atom with 6 protons and 6 neutrons, which we call 1 atomic mass unit protons have a mass of 1amu electrons have a mass of amu,

36 Some Problems How could beryllium have 4 protons stuck together in the nucleus? If a beryllium atom has 4 protons, then it should weigh 4 amu; but it actually weighs 9.01 amu! Where is the extra mass coming from? each proton weighs 1 amu and the mass of the electrons is trivial

37 THERE MUST BE SOMETHING ELSE THERE! to answer these questions, Rutherford proposed that there was another particle in the nucleus it is called a have no charge and a mass of 1 amu mass = x g slightly heavier than a proton no charge

38 ELEMENTS each element has a unique number of protons in its nucleus the number of protons in the nucleus of an atom is called the = Z the elements are arranged on the current Periodic Table in order of their each element has a unique name and symbol symbol either one or two letters one capital letter or one capital letter + one lowercase

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40 STRUCTURE OF THE NUCLEUS Soddy discovered that the same element could have atoms with different masses, which he called there are 2 of chlorine found in nature, one that has a mass of about 35 amu and another that weighs about 37 amu The observed mass is a weighted average of the weights of all the naturally occurring atoms the percentage of an element that is 1 is called the isotope s natural abundance the atomic mass of chlorine is amu

41 all of an element are chemically identical undergo the same chemical reactions all of an element have the same number of protons of an element have different masses of an element have different numbers of neutrons are identified by their integer number = # protons + # neutrons

42 Mass Spectrometer

43 Mass Spectrometer

44 Mass Spectrum Result

45 a mass is a graph that gives the relative mass and relative abundance of each particle relative mass of the particle is plotted in the x-axis relative abundance of the particle is plotted in the y- axis

46 ATOMIC MASS we previously learned that not all atoms of an element have the same mass isotopes we generally use the average mass of all an element s atoms found in a sample in calculations however the average must take into account the abundance of each isotope in the sample we call the average mass the Atomic Mass fractional abundance of isotope n mass of isotope n

47 NEON

48 Example 2.5 If copper is 69.17% Cu-63 with a mass of amu and the rest Cu-65 with a mass of amu, find copper s atomic mass Given: Find: Concept Plan: Relationships: Atomic Solution: Check: Mass Cu-63 = 69.17%, amu Cu-65 = %, amu atomic mass, amu isotope masses, isotope fractions fractional Atomic Atomic abundance Mass Mass of isotope avg. atomic mass the average is between the two masses, closer to the major isotope n mass of isotope amu amu amu n

49 CHARGED ATOMS Ions + Ions Called Originate from - Ions Called Originate from

50 ATOMIC STRUCTURES OF IONS Anions are named by changing the ending of the name to - fluorine F + 1e - F oxygen O + 2e - O 2

51 ATOMIC STRUCTURES OF IONS Cations are named sodium Na Na + + 1e - calcium Ca Ca e -

52 D.MENDELEEV (1870) AND H.MOSLEY (1914) Law When the elements are arranged in order of increasing atomic (mass) number, certain sets of properties recur periodically

53 nm H 2 O a/b H 1 H 2 Periodic Pattern m Li Li 2 O b 7 LiH m Na 2 O Nab m/nm BeO Be a/b 9 BeH 2 m Mg nm B 2 O 3 a B 11 ( BH 3 ) n MgOm Al 2 O 3 b a/b Al 23 NaH24 MgH 2 27 (AlH 3 ) nm CO 2 nm N 2 O 5 nm O 2 a a C 12 CH 4 14 NH 3 nm/m SiO 2 Si 28 SiH 4 N nm P 4 O 10 nm SO 3 a a a P O 16 H 2 O S 31 PH 3 32 H 2 S nm F 19 HF nm Cl 2 O 7 a Cl 35.5 HCl m = metal, nm = nonmetal, m/nm = metalloid a = acidic oxide, b = basic oxide, a/b = amphoteric oxide

54 Mendeleev s Periodic Chart 1871

55 Mendeleev s Predictions for Ekasilicon (Germanium) Property Silicon s Tin s Predicted Measured Props Props Value Value Atomic Mass Color Grey White metal Grey Grey- White Density Reaction w/ Acid & Base Resists Acid, Reacts Base Reacts Acid, Resists Base Resists Both Resists Both Oxide SiO 2 SnO 2 Eks 1 O 2 GeO 2

56 METALS List typical or descriptive properties Give the operational definition of a metal:

57 NONMETALS ARE FOUND IN ALL 3 Sulfur, S(s) List typical or descriptive properties Give the operational definition of a nonmetal: Bromine, Br 2 (l) Chlorine, Cl 2 (l)

58 METALLOIDS show some properties of metals and some of nonmetals also known as conductors Properties of Silicon shiny conducts electricity poorly does not conduct heat well brittle

59 Patterns in Metallic Character = Metal = Metalloid = Nonmetal

60 THE MODERN PERIODIC TABLE Elements with similar chemical and physical properties are in the are called Groups or Families designated by a number and letter at top rows are called each shows the pattern of properties repeated in the next period

61 The Modern Periodic Table Main Group = Representative Elements = A groups Transition Elements = B groups all metals Bottom Rows = Inner Transition Elements = Rare Earth Elements metals really belong in Period 6 & 7

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63 = Alkali Metals = Alkali Earth Metals = Noble Gases = Halogens = Lanthanides = Actinides = Transition Metals

64 Important Groups - Hydrogen nonmetal colorless, diatomic gas very low melting point and density reacts with nonmetals to form molecular compounds HCl is acidic gas H 2 O is a liquid reacts with metals to form hydrides metal hydrides react with water to form H 2 HX dissolves in water to form acids

65 Important Groups - Alkali Metals Group IA = Alkali Metals soft, low melting points, low density flame tests very reactive water-soluble compounds, colorless react with water to form basic (alkaline) solutions and H 2 2 Na + 2 H 2 O 2 NaOH + H 2 releases a lot of heat lithium sodium potassium rubidium cesium

66 Important Groups - Alkali Earth Metals Group IIA = Alkali Earth Metals harder, higher melting, and denser than alkali metals Mg alloys used as structural materials flame tests reactive form stable, insoluble oxides from which they are normally extracted oxides are basic reactivity with water to form H 2 Be = none; Mg = steam; Ca, Sr, Ba = cold water beryllium magnesium calcium strontium barium

67 Important Groups - Halogens Group VIIA = Halogens nonmetals all diatomic very reactive Cl 2, Br 2 react slowly with water Br 2 + H 2 O HBr + HOBr react with metals to form ionic compounds HX all acids HF weak < HCl < HBr < HI fluorine chlorine bromine iodine astatine

68 Important Groups - Noble Gases Group VIIIA = Noble Gases all gases very low melting and boiling points very unreactive, practically inert BECAUSE IT IS very hard to remove electron from or give an electron to helium neon argon krypton xenon

69 ION CHARGE AND THE PERIODIC TABLE the charge on an ion of a representative element can often be determined from an element s position on the Periodic Table metals Nonmetals main group metals, Charge = nonmetals, charge =

70 1A 2A 3A 5A 6A 7A Li +1 N -3 O -2 F -1 Na +1 Mg +2 Al +3 S -2 Cl -1 K +1 Ca +2 Se -2 Br -1 Rb +1 Sr +2 Te -2 I -1 Cs +1 Ba +2

71 The Mole

72 Counting Atoms by Moles WHY? The number of atoms we will use is x and we call this a mole 1 mole = x things Like 1 dozen = 12 things

73 Chemical Packages - Moles mole = number of particles equal to the number of atoms in 12 g of C-12 1 atom of C-12 weighs exactly 12 amu 1 mole of C-12 weighs exactly 12 g The number of particles in 1 mole is called Avogadro s Number = x mole of C atoms weighs g and has x atoms the average mass of a C atom is amu

74 Example 2.6 Calculate the number of atoms in 2.45 mol of copper Given: Find: Concept Plan: Relationships: mol Cu 2.45 mol Cu atoms Cu atoms 1mol atoms Cu 1 mol = x atoms 23 Solution: Check: 2.45 mol Cu atoms 10 1mol Cu atoms since atoms are small, the large number of atoms makes sense 23

75 RELATIONSHIP BETWEEN MOLES AND MASS The mass of one mole of atoms is called the

76 Mole and Mass Relationships Weight of Pieces in Weight of Substance 1 atom 1 mole 1 mole hydrogen amu x atoms g carbon amu x atoms g oxygen amu x atoms g sulfur amu x atoms g calcium amu x atoms g chlorine amu x atoms g copper amu x atoms g 1 mole sulfur g 1 mole carbon g

77 Example 2.7 Calculate the moles of carbon in g of pencil lead Given: Find: Concept Plan: Relationships: Solution: Check: g C mol C g C 1 mol C = g 1mol 12.01g g C mol mol C 1mol 12.01g since the given amount is much less than 1 mol C, the number makes sense -3 C

78 Example 2.8 How many copper atoms are in a penny weighing 3.10 g? Given: Find: Concept Plan: Relationships: Solution: Check: 3.10 g Cu atoms Cu g Cu mol Cu atoms Cu 1mol g 1 mol Cu = g, 1 mol = x g Cu mol Cu g Cu atoms Cu atoms 1mol mol atoms since the given amount is much less than 1 mol Cu, the number makes sense 23 23

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80 What element is defined by the following information? p+ = 11 n = 12 e- = 11 A) sodium B) vanadium C) magnesium D) titanium

81 p+ = 11 n = 12 e- = 11 A) sodium B) vanadium C) magnesium D) titanium Answer: A

82 What element is defined by the following information? p+ = 17 n = 20 e- = 17 A) calcium B) rubidium C) chlorine D) neon E) oxygen

83 p+ = 17 n = 20 e- = 17 A) calcium B) rubidium C) chlorine D) neon E) oxygen Answer: C

84 What does X represent in the symbol? 80 X 35 A) mercury B) chlorine C) scandium D) bromine E) selenium

85 A) mercury B) chlorine C) scandium D) bromine E) selenium Answer: D

86 Determine the number of protons, neutrons and electrons in : 40 X 18 A) p+ = 18 n = 18 e- = 22 B) p+ = 18 n = 22 e- = 18 C) p+ = 22 n = 18 e- = 18 D) p+ = 18 n = 22 e- = 40 E) p+ = 40 n = 22 e- = 18 Answer: B

87 A) p+ = 18 n = 18 e- = 22 B) p+ = 18 n = 22 e- = 18 C) p+ = 22 n = 18 e- = 18 D) p+ = 18 n = 22 e- = 40 E) p+ = 40 n = 22 e- = 18 Answer: B

88 What species is represented by the following information? p+ = 12 n = 14 e- = 10 A) Si4+ B) Mg C) Ne D) Si E) Mg2+

89 p+ = 12 n = 14 e- = 10 A) Si4+ B) Mg C) Ne D) Si E) Mg2+ Answer: E

90 What species is represented by the following information? p+ = 17 n = 18 e- = 18 A) Cl B) Cl- C) Ar D) Ar+ E) Kr

91 p+ = 17 n = 18 e- = 18 A) Cl B) Cl- C) Ar D) Ar+ E) Kr Answer: B

92 Which of the following elements is a metal? A) As B) C C) I D) Sn E) Se

93 A) As B) C C) I D) Sn E) Se Answer: D

94 Which of the following elements is a halogen? A) Ne B) I C) O D) Mg E) K Answer: B

95 A) Ne B) I C) O D) Mg E) K Answer: B

96 Predict the charge that an aluminum ion would have. A) 5- B) 1+ C) 1- D) 2+ E) 3+

97 A) 5- B) 1+ C) 1- D) 2+ E) 3+ Answer: E

98 Two samples of potassium iodide are decomposed into their constituent elements. The first sample produced 13.0 g of potassium and 42.3 g of iodine. If the second sample produced 24.4 kg of potassium, how many kg of iodine were produced? A) 13.3 kg B) 22.5 kg C) 79.4 kg D) 44.4 kg E) 92.4 kg

99 A) 13.3 kg B) 22.5 kg C) 79.4 kg D) 44.4 kg E) 92.4 kg Answer: C

100 Calculate the atomic mass of silver if silver has 2 naturally occurring isotopes with the following masses andatural abundances: Ag amu 51.84% Ag amu 48.46% A) amu B) amu C) amu D) amu E) amu

101 A) amu B) amu C) amu D) amu E) amu Answer: E

102 How many xenon atoms are contained in 2.36 moles of xenon? A) xenon atoms B) xenon atoms C) xenon atoms D) xenon atoms E) xenon atoms Answer: C

103 A) xenon atoms B) xenon atoms C) xenon atoms D) xenon atoms E) xenon atoms Answer: C

104 What mass (in mg) does 2.63 moles of nickel have? A) 44.8 mg B) mg C) 129 mg D) 3.56 x 10 5 mg E) 1.54 x 10 5 mg

105 A) 44.8 mg B) mg C) 129 mg D) 3.56 x 10 5 mg E) 1.54 x 10 5 mg Answer: E

106 How many moles of Cs are contained in 595 kg of Cs? A) moles Cs B) moles Cs C) moles Cs D) moles Cs E) moles Cs

107 A) moles Cs B) moles Cs C) moles Cs D) moles Cs E) moles Cs Answer: B