Presentation on theme: "Unit #3 Atomic Structure"— Presentation transcript:
1Unit #3 Atomic Structure What is an Atom?Unit #3 Atomic Structure
2Review from 8th Grade OBJECTIVES: Identify the subatomic particles Explain how the atomic number identifies an element.Use the atomic number and mass number of an element to find the numbers of protons, electrons, and neutronsReview key terms
3Subatomic particles Relative mass Actual mass (g) Name Symbol Charge Electrone--11/18409.11 x 10-28Protonp++111.67 x 10-24Neutronn011.67 x 10-24
4Counting 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
5Counting the Pieces Protons: equal to atomic number Neutrons: Mass Number – Atomic NumberElectrons: In a neutral atom equal to atomic number
6SymbolsContain the symbol of the element, the mass number and the atomic number.
7SymbolsContain the symbol of the element, the mass number and the atomic number.MassnumberXAtomicnumber
8F Symbols 19 9 Find the number of protons number of neutrons number of electronsAtomic numberMass Number19F9
9Br Symbols 80 35 Find the number of protons number of neutrons number of electronsAtomic numberMass Number80Br35
10Symbolsif an element has an atomic number of 34 and a mass number of 78 what is thenumber of protonsnumber of neutronsnumber of electronsComplete symbol
11Symbols if an element has 91 protons and 140 neutrons what is the Atomic numberMass numbernumber of electronsComplete symbol
12Symbols if an element has 78 electrons and 117 neutrons what is the Atomic numberMass numberNumber of protonsComplete symbol
13What if Atoms Aren’t Neutral Ions: charged atoms resulting from the loss or gain of electrons
14What if Atoms Aren’t Neutral Anion: negatively charged ion; result from gaining electronsTake the number of electrons in a neutral atom and add the absolute value of the chargeIdentify:Number of ProtonsNumber of NeutronsNumber of Electrons811-Br35
15What if Atoms Aren’t Neutral Cation: positively charged ion; result from the loss of electronsTake the number of electrons in a neutral atom and subtract the value of the chargeIdentify:Number of ProtonsNumber of NeutronsNumber of Electrons27Al3+13
16Distinguishing Between Atoms OBJECTIVES:Explain how isotopes differ, and why the atomic masses of elements are not whole numbers.
17Distinguishing Between Atoms OBJECTIVES:Calculate the average atomic mass of an element from isotope data.
18IsotopesAtoms of the same element can have different numbers of neutronsDifferent mass numbersCalled isotopes
19Naming IsotopesWe can also put the mass number after the name of the element.carbon- 12carbon -14uranium-235
20Atomic Mass How heavy is an atom of oxygen? There are different kinds of oxygen atomsWe are more concerned with average atomic massAverage atomic mass is based on abundance of each element in nature.We don’t use grams because the numbers would be too small
21Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) It is one twelfth the mass of a carbon- 12 atomEach isotope has its own atomic mass, thus we determine the average from percent abundance
22Calculating averagesConvert the percent to a decimal (move the decimal 2 places to the left or divide by 100)Multiply the atomic mass by it’s percent (expressed as a decimal), then add the results.
23Calculating AveragesCalculating the Average Atomic Mass is similar to calculating your grade in this classPercent of GradeStudent's AverageTests 35%89Quizzes 25%95Labs 20%35Homework 20%100
24Calculating AveragesIf Bromine-79 has an abundance of 50.69% and Bromine-81 has an abundance of % what is the average atomic mass of Bromine?Why is it better to use the mass of an individual isotope for the mass number rather than round the number from the periodic table?
25Atomic MassMagnesium has three isotopes % magnesium-24 with a mass of amu, 10.00% magnesium-25 with a mass of amu, and the rest magnesium- 26 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
26Atomic Mass Is not a whole number because it is an average. are the decimal numbers on the periodic table.
27History 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.
28Democritus and Leucippus Leucippus was the first person to come up with the idea of the atomDemocritus was a student of Leucippus and expanded on his idea
29Democritus Democritus added: Matter is composed of atoms which move through empty spaceAtoms are solid, homogeneous, indestructible, and indivisibleDifferent atoms have different shapes and sizesThe size, shape, and movement of atoms determine their properties
30Greek Aristotle - Famous philosopher All substances are made of 4 elementsFire - HotAir - lightEarth - cool, heavyWater - wetBlend these in different proportions to get all substances
31AristotleThere was no scientific evidence to back up either Democritus or Aristotle, but people believed Aristotle based on reputationAristotle’s theory persisted for 2,000 years
32Leading to the modern theory 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.Saw atoms as small solid spheres. Billiard Ball Model.
33Dalton’s Atomic Theory All matter is made of tiny indivisible particles called atoms.Atoms of the same element are identical, those of atoms of different elements 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.
34Laws Related to Atomic Theory Law of Conservation of Mass- Antoine Lavoisier; states that matter is neither created nor destroyed in chemical reactionsLaw of Definite Proportions- Joseph Proust; states that all compounds contain the same elements in the same ratioLaw of Multiple Proportions- John Dalton; elements combine in small whole number ratios
35Just 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
36Structure of the Nuclear Atom OBJECTIVES:Distinguish among protons, electrons, and neutrons in terms of relative mass and charge.Describe the structure of an atom, including the location of the protons, electrons, and neutrons with respect to the nucleus.
37Parts 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.
42- + Thomson’s Experiment Voltage source-+Passing an electric current makes a beam appear to move from the negative to the positive end
43- + Thomson’s Experiment Voltage source-+Passing an electric current makes a beam appear to move from the negative to the positive end
44- + Thomson’s Experiment Voltage source-+Passing an electric current makes a beam appear to move from the negative to the positive end
45- + Thomson’s Experiment Voltage source-+Passing an electric current makes a beam appear to move from the negative to the positive end
46Thomson’s ExperimentVoltage sourceBy adding an electric field
47Thomson’s ExperimentVoltage source+-By adding an electric field
48Thomson’s ExperimentVoltage source+-By adding an electric field
49Thomson’s ExperimentVoltage source+-By adding an electric field
50Thomson’s ExperimentVoltage source+-By adding an electric field
51Thomson’s ExperimentVoltage source+-By adding an electric field
52Thomson’s ExperimentVoltage source+-By adding an electric field he found that the moving pieces were negative
53Plum Pudding Model Proposed by JJ Thomson Said the atom had a uniform positive charge in which the negatively charged electrons resided
54Other particlesProton - positively charged pieces times heavier than the electron – by E. GoldsteinNeutron - no charge but the same mass as a proton – by J. ChadwickWhere are the pieces?
55Millikan’s Oil DropJJ Thomson used the cathode ray to find the mass to charge ratio of an electron.He did not know the mass or charge, only the ratioMillikan’s Oil Drop experiment determined the charge of an electron
57Millikan’s Experiment X-raysX-rays give some electrons a charge.
58Millikan’s Experiment From the mass of the drop and the charge onthe plates, he calculated the mass of an electronSome drops would hover
59Rutherford’s experiment Ernest Rutherford -English physicist. (1910)Believed in the plum pudding model of the atomWanted 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.
60Rutherford’s experiment When an alpha particle hits a fluorescent screen, it glows.Here’s what it looked like
62He 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.
70Density 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.
71Bohr ModelBohr worked with the concepts of energy, wavelength and frequencyEach color of light is associated with a different energyEach atom gives off its own unique color so..Electrons of diiferent atoms have different energies
72Bohr Model Each atom has its own specific electron arrangement Electrons are in Energy levels in the atomWhen an electron goes from an excited state back down to its ground state the atom emits light
74The Bohr Model Doesn’t work. Only works for hydrogen atoms. Electrons don’t move in circles.The quantization of energy is right, but not because they are circling like planets.Back to the drawing board
75The Quantum Mechanical Model A totally new approach.De Broglie said matter could be like a wave, like standing waves.The vibrations of a stringed instrument.More on this in Unit # 4
76Models of the Atom to Know DaltonsThomsonsRutherfordBohrQuantum