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Transcription

1 Name: RegentsChemistry:Mr.Palermo Notes:Unit4:Atomics!

2 Name: $ Key$Ideas$ Themodernmodeloftheatomhasevolvedoveralongperiodoftimethroughtheworkofmany scientists.(3.1a) Eachatomhasanucleus,withanoverallpositivecharge,surroundedbyoneormorenegatively chargedelectrons.(3.1b) Subatomicparticlescontainedinthenucleusincludeprotonsandneutrons.(3.1c) Theprotonispositivelycharged,andtheneutronhasnocharge.Theelectronisnegatively charged.(3.1d) Protonsandelectronshaveequalbutoppositecharges.Thenumberofprotonsequalsthenumberof electronsinanatom.(3.1e) Themassofeachprotonandeachneutronisapproximatelyequaltooneatomicmassunit.An electronismuchlessmassivethanaprotonoraneutron.(3.1f) Thenumberofprotonsinanatom(atomicnumber)identifiestheelement.Thesumoftheprotons andneutronsinanatom(massnumber)identifiesanisotope.commonnotationsthatrepresent isotopesinclude:14c,14c,carbonl14,cl14.(3.1g) InthewaveLmechanicalmodel(electroncloudmodel),theelectronsareinorbitals,whichare definedastheregionsofthemostprobableelectronlocation(groundstate).(3.1h) Eachelectroninanatomhasitsowndistinctamountofenergy.(3.1i) Whenanelectroninanatomgainsaspecificamountofenergy,theelectronisatahigherenergy state(excitedstate).(3.1j) Whenanelectronreturnsfromahigherenergystatetoalowerenergystate,aspecificamountof energyisemitted.thisemittedenergycanbeusedtoidentifyanelement.(3.1k) Theoutermostelectronsinanatomarecalledthevalenceelectrons.Ingeneral,thenumberof valenceelectronsaffectsthechemicalpropertiesofanelement.(3.1l) Atomsofanelementthatcontainthesamenumberofprotonsbutadifferentnumberofneutronsare calledisotopesofthatelement.(3.1m) Theaverageatomicmassofanelementistheweightedaverageofthemassesofitsnaturally occurringisotopes.(3.1n) TheplacementorlocationofelementsonthePeriodicTablegivesanindicationofphysicaland chemicalpropertiesofthatelement.theelementsontheperiodictablearearrangedinorderof increasingatomicnumber.(3.1y) ForGroups1,2,and13L18onthePeriodicTable,elementswithinthesamegrouphavethesame numberofvalenceelectrons(heliumisanexception)andthereforesimilarchemicalproperties. (3.1z)

3 UNIT 4: ATOMICS LESSON 4.1: ATOMIC THEORY Objective: By the end of this video you will be able to:! Describe how the modern model of the atom has evolved over a long period of time through the work of many scientists! Relate experimental evidence to models of the atom! Describe in detail Rutherford s Experiment and the conclusions he made Democritus ( B.C.) His Model of the Atom: - Atom is the smallest piece that any substance can be broken down into. Dalton (1808) His Model of Atom: - All elements composed of tiny particles called ATOMS - Atoms of same element are identical; atoms of different elements are different J. J. Thompson (1897) Discovered ELECTRONS using a cathode ray tube. His Model of the Atom: - plum pudding model - Atom is positively charged with negative electrons stuck in it. Dalton s Model: Solid indestructible sphere 1

4 Cathode Ray Tube (CRT) A Vacuum tube where a beam of electrons pass through from left to right. Thomson used it to discover electrons, - Concluded they are negatively charged. CRT Television! Describe how the modern model of the atom has evolved over a long period of time through the work of many scientists! Relate experimental evidence to models of the atom Ernest Rutherford (1911) Rutherford s Gold Foil Experiment Discovered the NUCLEUS His Model of the Atom: - Small dense positive nucleus - Atom is mostly empty space The experiment: Shot positively charged alpha particles at gold foil. The Result: Most particles went straight through. A few were deflected. 2

5 His Conclusion: (you must know these) Example: 1. Atom is mostly empty space 2. Small dense positive center (nucleus) When alpha particles are used to bombard gold foil, most of the alpha particles pass through undeflected. This result indicates that most of the volume of a gold atom consists of. 1. a nucleus 2. neutrons 3. protons 4. unoccupied space! Describe in detail Rutherford s Experiment and the conclusions he made MODERN THEORIES Niels Bohr (1913) His Model of the Atom: Electrons travel around the nucleus in well-defined paths called ORBITS (like planets in a solar system) Electrons in different orbits possess different amounts of ENERGY. Wave-Mechanical Model (present day model) Discovery: Can only determine the probability of finding an electron Model of the Atom: - Electrons found in ORBITALS 3

6 ! Describe how the modern model of the atom has evolved over a long period of time through the work of many scientists! Relate experimental evidence to models of the atom You should be able to:! Describe how the modern model of the atom has evolved over a long period of time through the work of many scientists! Relate experimental evidence to models of the atom! Describe in detail Rutherford s Experiment and the conclusions he made Objective: By the end of this video you will be able to: LESSON 4.2: SUBATOMIC PARTICLES! Identify the subatomic particles of an atom (proton, neutron, and electron)! Determine the number of protons, neutrons, electrons, nucleons and nuclear charge in a neutral atom Subatomic Particles Name: Symbol Charge Mass The Parts of the atom Nucleons = (protons + neutrons) Proton (located in the nucleus) Neutron (located in the nucleus) p amu n 0 0 1amu Electron (located outside the nucleus) e /1836 amu amu = atomic mass unit 1 amu = 1/12 th mass of a carbon-12 atom 4

7 ! Identify the subatomic particles of an atom (proton, neutron, and electron) Atomic Number " Equal to the number of protons " Every element has its own atomic number " How periodic table is arranged 6 C Mass Number " Equal to the sum of the protons and the neutrons (whole number) " Can be written as carbon To find: # of protons C Look up atomic number on Periodic Table Ex. Lithium has 3 protons To find: # of electrons Equal to the # of protons in a neutral atom Ex. Lithium has 3 electrons To find: # of neutrons Protons + Neutrons = Mass # of neutrons = mass # - number of protons Ex. Lithium has 4 neutrons (7 3) = 4 5

8 ! Determine the number of protons, neutrons, electrons in a neutral atom To find: Nuclear Charge Equal to the number of protons Ex. Lithium has a +3 nuclear charge Example: Fill in the table Element Atomic # Mass # # of protons # of neutrons # of electron s! Determine the number of nucleons and nuclear charge in a neutral atom Carbon (C) You should be able to:! Identify the subatomic particles of an atom (proton, neutron, and electron)! Determine the number of protons, neutrons, electrons, nucleons and nuclear charge in a neutral atom LESSON 4.3: IONS 6

9 Objective: By the end of this video you will be able to:! Determine the number of protons, neutrons, and electrons in an ion Ions Charged particles Formed when atoms gain or lose electrons cation: The atom loses e- becomes positively charged Ex. Na + anion: the atom becomes negatively charged Ex. Cl Example: Example: Element Fe Atomic # Mass # p n e Element Br Atomic # Mass # p n e Fe Br 1-7

10 ! Determine the number of protons, neutrons, and electrons in an ion You should be able to:! Determine the number of protons, neutrons, and electrons in an ion Objective: By the end of this video you will be able to: LESSON 4.4: ISOTOPES AVERAGE ATOMIC MASS Differentiate between atomic number, mass number, and (average) atomic mass! Calculate the number of neutrons in an isotope! Calculate the (average) atomic mass for all isotopes of an element Isotopes Isotope Symbols Elements that have the same atomic number but different mass (different # of neutrons) Show the mass of isotope Same atomic #, different mass # Ex. isotope symbol of element X X Mass # Atomic # 8

11 Common Isotopes of Hydrogen Name Symbol #p #e #n Mass Protium 1H Deuterium 2 H Tritium 3H Example: The isotope symbol for Carbon C How many neutrons does it have? 14 6 = 8 Mass # Proton # Example: Write the isotope symbol for: Oxygen O! Differentiate between atomic number, mass number, and (average) atomic mass! Calculate the number of neutrons in an isotope How many neutrons does it have? Why is atomic mass not a whole number? CALCULATING AVERAGE ATOMIC MASS The atomic mass on the periodic table is a weighted average of the isotopes of the elements. The weighted atomic mass takes into account the relative abundances (amounts) of all the naturally occurring isotopes. 9

12 Example of a general weighted average Your grade in chemistry " 50% exams 85 " 10% quizzes 100. " 15% labs 95 " 25% HW/CW 80. (50 x 85) + (10 x 100.) + (15 x 95) + (25 x 80.) = 100 = 87 avg. Example: Determine avg atomic mass Boron-10 Boron % amu 80.22% amu Step 1: Multiply the mass of each isotope by its percent abundance then divide by 100 (19.78 x ) + (80.22 x ) = amu Example Determine weighted atomic mass Potassium % amu Potassium % amu! Calculate the (average) atomic mass for all isotopes of an element You should be able to:! Differentiate between atomic number, mass number, and (average) atomic mass! Calculate the number of neutrons in an isotope! Calculate the (average) atomic mass for all isotopes of an element LESSON 4.5: BOHR DIAGRAMS 10

13 Objective: By the end of this video you will be able to:! Construct Bohr diagrams for atoms and ions Bohr Models How do electrons orbit the nucleus? In energy levels Each principal energy level: - is a fixed distance from the nucleus - can hold a specific number of electrons - has a definite amount of energy The greater the distance from the nucleus the greater the energy of the electrons in it. The ORBITS are called principal energy levels or shells. How many electrons can each shell hold? 2n 2 n = the period number from reference table Increasing Energy Ex. Max # of electrons in 1 st shell is 2(1) 2 = 2 e- Drawing Bohr Diagrams Example: Bohr diagram of Mg 1. Look up electron configuration on Periodic table (if its an ion add/subtract the e- from the outermost energy level) 2. Draw a circle for nucleus and notate # of protons and neutrons in it. 3. Draw in energy levels and notate the # of electrons in each shell 12 p+ 12 n 0 2 e- 8 e- 2 e- 11

14 Example: Bohr diagram of Mg +2 Example: Bohr diagram of Ca p+ 12 n 0 2 e- 8 e-! Construct Bohr diagrams for atoms and ions You should be able to:! Construct Bohr diagrams for atoms and ions Objective: By the end of this video you will be able to: LESSON 4.6: GROUND VS EXCITED STATE BRIGHT LINE SPECTRUM! Differentiate between excited and ground state! Explain how light is produced! Identify substances based upon their bright line spectra 12

15 Ground State vs. Excited State EXAMPLE: Possible Excited States for Sodium " Ground State- When electrons occupy the LOWEST available ENERGY LEVELS. (configuration on periodic table) Na (ground state) Na (possible excited state) Na (another possible excited state) Na (another possible excited state) Excited State- Electrons NO LONGER occupy the lowest available energy levels (different than electron configuration) How do you tell if the configuration is ground or excited state? Example: Add up total # of electrons in configuration Determine element If it matches element configuration on periodic table = GROUND If it doesn t match = EXCITED Identify the electron configuration as being ground state or excited state: = 9 Fluorine Excited State More Examples:! Differentiate between excited and ground state *****Remember when in excited state the total # of electrons DOES NOT change 13

16 Absorption BRIGHT LINE SPECTRUM Electrons absorb energy as they move to higher energy levels (excited state) This excited state is temporary and unstable. Emission Light Electrons are negatively charged and therefore attracted to positive nucleus so eventually they fall back to ground state and give off the energy they absorbed as light energy. The color of the light is determined by the amount of energy lost by the electron when it drops back to the ground state. Electromagnetic Spectrum Example: Possible Ways an electron can fall back to ground state from 4 th energy level. 1. From the 4th to the 1st energy level 2. From the 4th to the 3rd to the 1st energy level 3. From the 4th to the 2nd to the 1st energy level. 4. From the 4th to the 3rd to the 2nd to the 1st energy level. 14

17 Bright Line Spectra Example: What Gases Comprise the Unknown? Each element has its own bright line spectra that is unique. (like a fingerprint) Can be used to identify an unknown mixture of gases.! Explain how light is produced! Identify substances based upon their bright line spectra You should be able to:! Differentiate between excited and ground state! Explain how light is produced! Identify substances based upon their bright line spectra Objective: By the end of this video you will be able to:! Construct Lewis dot diagrams for atoms and ions LESSON 4.7: LEWIS DOT DIAGRAMS 15

18 Lewis Dot Diagrams (electron dot diagrams) Only show VALENCE ELECTRONS Valence shell: outer most shell of an atom that contains electrons Valence electrons: electrons that occupy the valence shell (last number in electron configuration) Steps for drawing dot diagrams: 1. Draw the elements symbol 2. Locate valence electron # (last number of electron configuration) 3. Pair the first 2 electrons they deal out any remaining one at a time to other 3 sides. Example: Draw dot diagram for Carbon Example: Draw dot diagram of Na C Na Example: Draw dot diagram of Al Al! Construct Lewis dot diagrams for atoms 16

19 Lewis Diagrams: Ions 1. Draw brackets around the element symbol 2. Write charge of ion outside bracket on top right corner of symbol 3. Positive ions no dots 4. Negative ions 8 dots [ Na ] + Remove 1 electron from the valence shell of K Example: K + Na + = 2-8 Example: S -2 Example: P and P -3 Add 2 electrons to the 6 that S normally has in its valence shell! Construct Lewis dot diagrams for ions You should be able to:! Construct Lewis dot diagrams for atoms and ions 17