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Atoms and Elements John Dalton 1766-1844 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 MiniBiographies http://poohbah.cem.msu.edu/Portraits Scanning Tunneling Microscope 1986 Nobel Prize Operation of a STM Superconducting YBa2Cu3O7 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 Scientific Revolution • late 16th century, the scientific approach to understanding nature • next 150+ years, observations about nature were made that could not easily be explained Aristotelian approach Law of Conservation of Mass total m reactants = total m of products Antoine Lavoisier 1743-1794 Reaction of Sodium with Chlorine to Make Sodium Chloride 7.7 g Na + 11.9 g Cl2 19.6 g NaCl LAW OF DEFINITE PROPORTIONS All samples of a given compound, regardless of their source or how they were prepared, have the ___________________ ___________________ Joseph Proust 1754-1826 Proportions in Sodium Chloride a 100.0 g sample of sodium mass of Cl 60.7 g 1.54 chloride contains 39.3 g of sodium mass of Na 39.3 g and 60.7 g of chlorine a 200.0 g sample of sodium mass of Cl 121.4 g 1.54 chloride contains 78.6 g of sodium mass of Na 78.6 g and 121.4 g of chlorine a 58.44 g sample of sodium mass of Cl 35.44 g 1.541 chloride contains 22.99 g of sodium mass of Na 22.99 g and 35.44 g of chlorine 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 1766-1844 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 1 g of carbon in carbon dioxide mass of oxygen that combines with 1 g of carbon in carbon monoxide 2.67 g 1.33 g 2 DALTON’S ATOMIC THEORY 1) 2) 3) 4) Each element is composed of tiny, indestructible particles called atoms …still correct? All atoms of a given element has the same mass and other properties that distinguish them from atoms of other elements…still correct? Atoms combine in simple, whole-number ratios to form molecules of compounds In a chemical reaction, atoms of one element cannot change into atoms of another element they simply rearrange the way they are attached Some Notes on Charge Cathode Ray Tubes anode cathode 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 Thomson’s Experiment 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 -1.76 x 108 C/g the charge/mass of the hydrogen ion is +9.58 x 104 C/g 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! the only way for this to be true is if these particles were pieces of atoms later experiments by Millikan showed that the particle did have the same amount of charge as the hydrogen ion 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 ________ Millikan’s Oil Drop Experiment Electrons • • • • electrons are particles found in all atoms cathode rays are streams of electrons the electron has a charge of -1.60 x 1019 C the electron has a mass of 9.1 x 10-28 g A New Theory of the Atom Thomson’s Plum Pudding Atom or maybe a raisins in oatmeal model 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 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 ~1/2000th H atom and – charge _______________that are energy rays, not particles Rutherford’s Experiment How can you prove something is empty? Rutherford’s Experiment Alpha Particles Striking Screen Radioactive Sample Lead Box Gold Foil Fluorescent Screen 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.” RUTHERFORD’S CONCLUSIONS Atom mostly _______________________ Atom contains a dense ______ that was small in volume compared to the atom but large in mass because almost all the particles went straight through because ________________________________ This dense particle was __________ charged because of the large ______________ of some of the particles Plum Pudding Atom • • • • • • • • • • a few of the particles do not go through • • • • • • • • • • • • if atom was like a plum pudding, all the particles should go straight through Nuclear Atom . . most particles go straight through . some particles go through, but are deflected RUTHERFORD’S INTERPRETATION – THE NUCLEAR MODEL 1) The atom contains a tiny dense center called the ______________________ 2) The _______ has essentially the entire ____ of the atom 3) the _______ weigh so little they give practically no mass to the atom The ______ is _________ charged 4) the amount of space taken by the ________ is only about 1/10 trillionth the volume of the atom the amount of positive charge balances the negative charge of the electrons The electrons are dispersed in the empty space of the atom surrounding the nucleus 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 = +1.60 x 1019 C mass = 1.67262 x 10-24 g For an atom to be neutral there must be equal ________________________ Relative Mass and Charge • we generally talk about the mass of atoms by comparing it to 1/12th 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 0.00055 amu, 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 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 = 1.67493 x 10-24 g slightly no heavier than a proton charge 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 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 35.45 amu 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 Mass Spectrometer Mass Spectrometer Mass Spectrum Result • 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 yaxis ATOMIC MASS we previously learned that not all atoms of an element have the same mass we generally use the average mass of all an element’s atoms found in a sample in calculations isotopes 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 NEON Example 2.5 If copper is 69.17% Cu-63 with a mass of 62.9396 amu and the rest Cu-65 with a mass of 64.9278 amu, find copper’s atomic mass Given: Find: Concept Plan: Cu-63 = 69.17%, 62.9396 amu Cu-65 = 100-69.17%, 64.9278 amu atomic mass, amu Relationships: Atomic Mass Solution: isotope masses, isotope fractions avg. atomic mass fractional abundance of isotope Atomic Mass n mass of isotope 0.6917 62.9396 amu 0.3083 64.9278 amu Atomic Mass 63.5525 63.55 amu Check: the average is between the two masses, closer to the major isotope n CHARGED ATOMS Ions + Ions Called______________ Originate from _________ - Ions Called______________ Originate from _________ ATOMIC STRUCTURES OF IONS Anions are named by changing the ending of the name to -_____________ fluorine F + 1e- F─ _________________ oxygen O + 2e- O2─ ___________ ATOMIC STRUCTURES OF IONS Cations are named ___________________ sodium calcium Na Ca Na+ + 1eCa2+ + 2e- _________ __________ 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 Periodic Pattern nm H2O a/b H 1 H2 m Li2O m/nm BeOnm B2O3 nm CO2 nm N2O5 nm O2 nm Li b Be a/b B a C a N a O F 7 LiH 9 BeH2 11 ( BH3)n 12 CH4 14 NH3 16 H2O 19 HF m Na2O m MgO m Al2O3 nm/m SiO2nm P4O10nm SO3 nm Cl2O7 Na b Mg b Al a/b Si a P a S a Cl a 23 NaH24 MgH2 27 (AlH3) 28 SiH4 31 PH3 32 H2S 35.5 HCl m = metal, nm = nonmetal, m/nm = metalloid a = acidic oxide, b = basic oxide, a/b = amphoteric oxide Mendeleev’s Periodic Chart 1871 Mendeleev’s Predictions for Ekasilicon (Germanium) Property Atomic Mass Color Silicon’s Props 28 Tin’s Props 118 Grey Grey 5.5 GreyWhite 5.4 Resists Both Resists Both Eks1O2 GeO2 Density 2.32 White metal 7.28 Reaction w/ Acid & Base Resists Acid, Reacts Base SiO2 Reacts Acid, Resists Base SnO2 Oxide Predicted Measured Value Value 72 72.6 METALS List typical or descriptive properties __________________________________ __________________________________ __________________________________ __________________________________ __________________________________ Give the operational definition of a metal: ________________________________ ________________________________ NONMETALS ARE FOUND IN ALL 3 ______________ Sulfur, S(s) List typical or descriptive properties _________________________________ _________________________________ _________________________________ _________________________________ _________________________________ Give the operational definition of a nonmetal: ________________________________ ________________________________ Bromine, Br2(l) Chlorine, Cl2(l) 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 Patterns in Metallic Character = Metal = Metalloid = Nonmetal 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 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 = Alkali Metals = Halogens = Alkali Earth Metals = Lanthanides = Noble Gases = Actinides = Transition Metals Important Groups - Hydrogen • nonmetal • colorless, diatomic gas very low melting point and density • reacts with nonmetals to form molecular compounds HCl is acidic gas H2O is a liquid • reacts with metals to form hydrides metal hydrides react with water to form H2 • HX dissolves in water to form acids Important Groups - Alkali Metals • Group IA = Alkali Metals • soft, low melting points, low density lithium • flame tests • very reactive • water-soluble compounds, colorless sodium potassium rubidium • react with water to form basic (alkaline) solutions and H2 2 Na + 2 H2O 2 NaOH + H2 releases a lot of heat cesium 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 beryllium magnesium • reactive calcium • form stable, insoluble oxides from strontium • • which they are normally extracted oxides are basic barium reactivity with water to form H2 Be = none; Mg = steam; Ca, Sr, Ba = cold water Important Groups - Halogens • Group VIIA = Halogens • nonmetals fluorine • all diatomic chlorine • very reactive • Cl2, Br2 react slowly with water bromine Br2 + H2O HBr + HOBr • react with metals to form ionic • compounds HX all acids HF weak < HCl < HBr < HI iodine astatine Important Groups - Noble Gases • Group VIIIA = Noble Gases • all gases very low melting and boiling points helium neon • very unreactive, practically • • inert BECAUSE IT IS very hard to remove electron from or give an electron to argon krypton xenon 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 = ________________ 1A 2A 3A Li+1 Na+1 Mg+2 Al+3 5A 6A 7A N-3 O-2 F-1 S-2 Cl-1 K+1 Ca+2 Se-2 Br-1 Rb+1 Sr+2 Te-2 I-1 Cs+1 Ba+2 The Mole Counting Atoms by Moles WHY? • The number of atoms we will use is 6.022 x 1023 and we call this a mole 1 mole = 6.022 x 1023 things Like 1 dozen = 12 things 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 = 6.0221421 x 1023 1 mole of C atoms weighs 12.01 g and has 6.022 x 1023 atoms the average mass of a C atom is 12.01 amu Example 2.6 Calculate the number of atoms in 2.45 mol of copper Given: Find: Concept Plan: 2.45 mol Cu atoms Cu mol Cu atoms Cu 6.022 10 23 atoms 1 mol Relationships: Solution: 1 mol = 6.022 x 1023 atoms 6.022 1023 atoms 2.45 mol Cu 1 mol 1.48 1024 atoms Cu Check: since atoms are small, the large number of atoms makes sense RELATIONSHIP BETWEEN MOLES AND MASS The mass of one mole of atoms is called the _____________ Mole and Mass Relationships hydrogen carbon Weight of Pieces in 1 atom 1 mole 1.008 amu 6.022 x 1023 atoms 12.01 amu 6.022 x 1023 atoms Weight of 1 mole 1.008 g 12.01 g oxygen 16.00 amu 6.022 x 1023 atoms 16.00 g sulfur 32.06 amu 6.022 x 1023 atoms 32.06 g calcium 40.08 amu 6.022 x 1023 atoms 40.08 g chlorine 35.45 amu 6.022 x 1023 atoms 35.45 g copper 63.55 amu 6.022 x 1023 atoms 63.55 g Substance 1 mole sulfur 32.06 g 1 mole carbon 12.01 g Example 2.7 Calculate the moles of carbon in 0.0265 g of pencil lead Given: Find: Concept Plan: 0.0265 g C mol C gC mol C 1 mol 12.01 g Relationships: 1 mol C = 12.01 g Solution: 1 mol 0.0265 g C 12.01 g 2.21 10-3 mol C Check: since the given amount is much less than 1 mol C, the number makes sense 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 1 mol 63.55 g 1 mol Cu = 63.55 g, 1 mol = 6.022 x 1023 mol Cu atoms Cu 6.022 10 23 atoms 1 mol 1 mol Cu 6.022 10 23 atoms 3.10 g Cu 63.55 g Cu 1 mol 2.94 10 22 atoms Cu since the given amount is much less than 1 mol Cu, the number makes sense What element is defined by the following information? • • • • • p+ = 11 n° = 12 e- = 11 A) sodium B) vanadium C) magnesium D) titanium • • • • • • p+ = 11 n° = 12 e- = 11 A) sodium B) vanadium C) magnesium D) titanium Answer: A What element is defined by the following information? p+ = 17 n° = 20 e- = 17 • A) calcium • B) rubidium • C) chlorine • D) neon • E) oxygen p+ = 17 n° = 20 e- = 17 • A) calcium • B) rubidium • C) chlorine • D) neon • E) oxygen • Answer: C What does X represent in the symbol? 80 X 35 • • • • • A) mercury B) chlorine C) scandium D) bromine E) selenium • • • • • • A) mercury B) chlorine C) scandium D) bromine E) selenium Answer: D 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 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 What species is represented by the following information? • • • • • • p+ = 12 n° = 14 e- = 10 A) Si4+ B) Mg C) Ne D) Si E) Mg2+ p+ = 12 n° = 14 e- = 10 A) Si4+ B) Mg C) Ne D) Si E) Mg2+ Answer: E What species is represented by the following information? • • • • • • p+ = 17 n° = 18 e- = 18 A) Cl B) ClC) Ar D) Ar+ E) Kr p+ = 17 n° = 18 e- = 18 A) Cl B) ClC) Ar D) Ar+ E) Kr Answer: B Which of the following elements is a metal? • • • • • A) As B) C C) I D) Sn E) Se A) As B) C C) I D) Sn E) Se Answer: D Which of the following elements is a halogen? • • • • • • A) Ne B) I C) O D) Mg E) K Answer: B A) Ne B) I C) O D) Mg E) K Answer: B Predict the charge that an aluminum ion would have. • • • • • A) 5B) 1+ C) 1D) 2+ E) 3+ A) 5B) 1+ C) 1D) 2+ E) 3+ Answer: E 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 A) 13.3 kg B) 22.5 kg C) 79.4 kg D) 44.4 kg E) 92.4 kg Answer: C Calculate the atomic mass of silver if silver has 2 naturally occurring isotopes with the following masses andatural abundances: Ag-107 106.90509 amu 51.84% Ag-109 108.90476 amu 48.46% • A) 107.90 amu • B) 108.00 amu • C) 107.79 amu • D) 108.32 amu • E) 108.19 amu A) 107.90 amu B) 108.00 amu C) 107.79 amu D) 108.32 amu E) 108.19 amu Answer: E How many xenon atoms are contained in 2.36 moles of xenon? • • • • • • A) 3.92 × 1024 xenon atoms B) 2.55 × 1023 xenon atoms C) 1.42 × 1024 xenon atoms D) 7.91 × 1025 xenon atoms E) 1.87 × 1026 xenon atoms Answer: C A) 3.92 × 1024 xenon atoms B) 2.55 × 1023 xenon atoms C) 1.42 × 1024 xenon atoms D) 7.91 × 1025 xenon atoms E) 1.87 × 1026 xenon atoms Answer: C What mass (in mg) does 2.63 moles of nickel have? • • • • • A) 44.8 mg B) 2.23 × 104 mg C) 129 mg D) 3.56 x 105 mg E) 1.54 x 105 mg A) 44.8 mg B) 2.23 × 104 mg C) 129 mg D) 3.56 x 105 mg E) 1.54 x 105 mg Answer: E How many moles of Cs are contained in 595 kg of Cs? • • • • • A) 2.23 × 102 moles Cs B) 4.48 × 103 moles Cs C) 7.91 × 104 moles Cs D) 1.26 × 103 moles Cs E) 5.39 × 102 moles Cs A) 2.23 × 102 moles Cs B) 4.48 × 103 moles Cs C) 7.91 × 104 moles Cs D) 1.26 × 103 moles Cs E) 5.39 × 102 moles Cs Answer: B