3Section 5.1 AtomsOBJECTIVES:Describe the size of an atom.
4History of the atom Not the history of atom, but the idea of the atom. Original idea Ancient Greece (400 B.C.)Democritus and Leucippus- Greek philosophers.
5History of Atom Smallest possible piece? Looked at beach Made of sand Atomos - not to be cutLooked at beachMade of sandCut sand - smaller sand
6Another Greek Aristotle - Famous philosopher All substances are made of 4 elementsFire - HotAir - lightEarth - cool, heavyWater - wetBlend these in different proportions to get all substances
7Who Was Right? Greek society was slave based. Beneath famous to work with hands.Did not experiment.Greeks settled disagreements by argument.Aristotle was more famous.He won.His ideas carried through middle ages.Alchemists change lead to gold.
8Who’s Next? Late 1700’s - John Dalton- England. Teacher- summarized results of his experiments and those of others.Dalton’s Atomic TheoryCombined ideas of elements with that of atoms.
9Dalton’s Atomic Theory All matter is made of tiny indivisible particles called atoms.Atoms of the same element are identical, those of different atoms are different.Atoms of different elements combine in whole number ratios to form compounds.Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.
10Just How Small Is an Atom? Think of cutting a piece of lead into smaller and smaller piecesHow far can it be cut?An atom is the smallest particle of an element that retains the properties of that elementAtoms-very small: Fig. 5.2, p. 108still observable with proper instruments: Fig. 5.3, page 108
11Section 5.2 Structure of the Nuclear Atom OBJECTIVES:Distinguish among protons, electrons, and neutrons in terms of relative mass and charge.
12Section 5.2 Structure of the Nuclear Atom OBJECTIVES:Describe the structure of an atom, including the location of the protons, electrons, and neutrons with respect to the nucleus.
13Parts of Atoms J. J. Thomson - English physicist. 1897 Made a piece of equipment called a cathode ray tube.It is a vacuum tube - all the air has been pumped out.
18- + Thomson’s Experiment Voltage source-+Passing an electric current makes a beam appear to move from the negative to the positive end
19- + Thomson’s Experiment Voltage source-+Passing an electric current makes a beam appear to move from the negative to the positive end
20- + Thomson’s Experiment Voltage source-+Passing an electric current makes a beam appear to move from the negative to the positive end
21- + Thomson’s Experiment Voltage source-+Passing an electric current makes a beam appear to move from the negative to the positive end
22Thomson’s ExperimentVoltage sourceBy adding an electric field
23Thomson’s ExperimentVoltage source+-By adding an electric field
24Thomson’s ExperimentVoltage source+-By adding an electric field
25Thomson’s ExperimentVoltage source+-By adding an electric field
26Thomson’s ExperimentVoltage source+-By adding an electric field
27Thomson’s ExperimentVoltage source+-By adding an electric field
28Thomson’s ExperimentVoltage source+-By adding an electric field he found that the moving pieces were negative
29Other particlesProton - positively charged pieces 1840 times heavier than the electron – by E. GoldsteinNeutron - no charge but the same mass as a proton – by J. ChadwickWhere are the pieces?
30Rutherford’s experiment Ernest Rutherford -English physicist. (1910)Believed in the plum pudding model of the atom (discussed in Chapter 13).Wanted to see how big they are.Used radioactivity.Alpha particles - positively charged pieces- helium atoms minus electronsShot them at gold foil which can be made a few atoms thick.
31Rutherford’s experiment When an alpha particle hits a fluorescent screen, it glows.Here’s what it looked like (page 111)
33He ExpectedThe alpha particles to pass through without changing direction very much.Because…?…the positive charges were thought to be spread out evenly. Alone they were not enough to stop the alpha particles.
41Density and the AtomSince most of the particles went through, it was mostly empty space.Because the pieces turned so much, the positive pieces were heavy.Small volume, big mass, big density.This small dense positive area is the nucleus.
42Subatomic particles – p.111 RelativemassActualmass (g)NameSymbolChargeElectrone--11/18409.11 x 10-28Protonp++111.67 x 10-24Neutronn011.67 x 10-24
43Section 5.3 Distinguishing Between Atoms OBJECTIVES:Explain how the atomic number identifies an element.
44Section 5.3 Distinguishing Between Atoms OBJECTIVES:Use the atomic number and mass number of an element to find the numbers of protons, electrons, and neutrons.
45Section 5.3 Distinguishing Between Atoms OBJECTIVES:Explain how isotopes differ, and why the atomic masses of elements are not whole numbers.
46Section 5.3 Distinguishing Between Atoms OBJECTIVES:Calculate the average atomic mass of an element from isotope data.
47Counting the Pieces Atomic Number = number of protons in the nucleus # of protons determines kind of atom (since all protons are alike!)the same as the number of electrons in the neutral atom.Mass Number = the number of protons + neutrons.These account for most of mass
48SymbolsContain the symbol of the element, the mass number and the atomic number.
49SymbolsContain the symbol of the element, the mass number and the atomic number.MassnumberXAtomicnumber
50F Symbols 19 9 Find the number of protons number of neutrons number of electronsAtomic numberMass Number19F9
51Br Symbols 80 35 Find the number of protons number of neutrons number of electronsAtomic numberMass Number80Br35
52Symbolsif an element has an atomic number of 34 and a mass number of 78 what is thenumber of protonsnumber of neutronsnumber of electronsComplete symbol
53Symbols if an element has 91 protons and 140 neutrons what is the Atomic numberMass numbernumber of electronsComplete symbol
54Symbols if an element has 78 electrons and 117 neutrons what is the Atomic numberMass numbernumber of protonsComplete symbol
55Isotopes Dalton was wrong. Atoms of the same element can have different numbers of neutrons.different mass numbers.called isotopes.
56Naming IsotopesWe can also put the mass number after the name of the element.carbon- 12carbon -14uranium-235
57Atomic Mass How heavy is an atom of oxygen? There are different kinds of oxygen atoms.More concerned with average atomic mass.Based on abundance of each element in nature.Don’t use grams because the numbers would be too small.
58Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom.Each isotope has its own atomic mass, thus we determine the average from percent abundance.
59Calculating averagesMultiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results.Sample 5-5, p.120
60Atomic MassCalculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of amu and the rest has a mass of amu.
61Atomic MassMagnesium has three isotopes % magnesium 24 with a mass of amu, 10.00% magnesium 25 with a mass of amu, and the rest magnesium 25 with a mass of amu. What is the atomic mass of magnesium?If not told otherwise, the mass of the isotope is the mass number in amu
62Atomic Mass Is not a whole number because it is an average. are the decimal numbers on the periodic table.
63Section 5.4 The Periodic Table: Organizing the Elements OBJECTIVES:Describe the origin of the periodic table.
64Section 5.4 The Periodic Table: Organizing the Elements OBJECTIVES:Identify the position of groups, periods, and the transition metals in the periodic table.
65Development of the Periodic Table mid-1800s, about 70 elementsDmitri Mendeleev – Russian chemistArranged elements in order of increasing atomic massThus, the first “Periodic Table”
66Mendeleev Left blanks for undiscovered elements When discovered, good predictionProblems?Co and Ni; Ar and K; Te and I
67New way Henry Moseley – British physicist Arranged elements according to increasing atomic numberThe arrangement todayP.124 – long formSymbol, atomic number & mass
68Periodic table Horizontal rows = periods There are 7 periods Periodic law:Vertical column = group (or family)Similar physical & chemical prop.Identified by number & letter
69Areas of the periodic table Group A elements = representative elementsWide range of phys & chem prop.Metals: electrical conductors, have luster, ductile, malleable
70Metals Group IA – alkali metals Group 2A – alkaline earth metals Transition metals and Inner transition metals – Group BAll metals are solids at room temperature, except _____.
71NonmetalsNonmetals: generally nonlustrous, poor conductors of electricitySome gases (O, N, Cl); some are brittle solids (S); one is a fuming dark red liquid (Br)Group 7A – halogensGroup 0 – noble gases
72Division between metal & nonmetal Heavy, stair-step lineMetalloids border the lineProperties intermediate between metals and nonmetalsLearn the general behavior and trends of the elements, instead of memorizing each element property