3 NGSSS: SC912P8.4Explore the scientific theory of atoms (also known as atomic theory) by describing the structure of atoms in terms of protons, neutrons and electrons, and differentiate among these particles in terms of their mass, electrical charges and locations within the atom
4 Questions you should be able to answer by the end: What scientists helped to develop atomic theory?What part of atoms did Thomson discover?What part of atoms did Rutherford discover?
5 Origins of Atomic Theory DemocritusGreek philosopher in 4th century BCETiny, indivisible units and voidAtomos unable to be cut or dividedNo evidence; all conjecture and theory
6 Dalton’s Contribution 1808, British schoolteacher John Dalton performed experimentsAtoms DO exist!Atoms could form compoundsLaw of Definite Proportions
7 What’s the Answer?How was Dalton’s theory different from that of Democritus?Carbon makes up 27% of the mass of CO2. How many grams of C are there in 88g of CO2?
8 Thomson Contributes to the Development of Atomic Theory 1897, British scientist J.J. Thomson working with cathode raysDiscovered electrons, negatively charged particlesPlumPudding by another Thomson called Lord Calvin
9 Can you Explain? What was the Greek perspective of atoms? How did Dalton support and detract from the Greek perspective of atoms?How did JJ Thomson discover electrons?
10 Rutherford Breaks Away from the Pack! Was a student of ThomsonTested the idea that the mass of an atom was spread evenly over its volumeGold Foil experimentBounce back indicatesa concentrated centerHow would test that idea?
11 Gestation of The Planetary Model Begins . . . Rutherford concluded that atom’s positive charge is concentrated at the centerNucleus dense positively charged core of atomSo tiny that like a marble in a football stadiumNegative electrons orbit the nucleus
12 Rutherford’s Atomic Model No specific orbitsOnly established the existence of the positive nucleus
13 Who did what?ScientistContributionFirst proposed that the universe is made up of tiny, indivisible units called atomsCarried out scientific experiments that showed that atoms existShowed that atoms contain smaller particles called electronsShowed that the positive charge in an atom is concentrated in a nucleus at its center
15 NGSSS: SC912P8.4Explore the scientific theory of atoms (also known as atomic theory) by describing the structure of atoms in terms of protons, neutrons and electrons, and differentiate among these particles in terms of their ass, electrical charges and locations within the atom
16 By the end of the lesson, you should be able to answer: What do atoms of the same element have in common?What are isotopes?How is an element’s average atomic mass calculated?
17 Who did what? Rutherford Dalton Thomson Democritus ScientistContributionFirst proposed that the universe is made up of tiny, indivisible units called atomsCarried out scientific experiments that showed that atoms existShowed that atoms contain smaller particles called electronsShowed that the positive charge in an atom is concentrated in a nucleus at its centerDemocritusDaltonThomsonRutherford
18 Bohr and Chadwick: The next steps in Atomic Theory Development 1913, Danish physicist Neils BohrFixed orbits for the electronsJames Chadwick, Bohr’s studentFound the neutron in the nucleusLed to discovery of fission and the atomic bomb
19 Electron Cloud Model Established by 1926 Area where electrons are most likely to be found100,000 times larger than the diameter of the nucleusImpossible to accurately describe path and location at any given timeOrbital a region in which an electron is most likely to be
20 What is Inside an Atom Particle Charge Mass (kg) Location Proton +1 1.67 xInside the nucleusNeutronElectron-19.11 xOutside the nucleus
21 What Do Atoms of the Same Element Have in Common? The number of protons is the same!!!# of protons identify the atom and element
22 Balancing Charge with Electrons Protons positiveElectrons negative1 proton + 1 electron = neutral chargeGain/lose electron = ion (ionized atom)Ions are NOT neutral
23 The Electric Force Opposites attract Protons and electrons attract each otherFarther apart = less attraction
24 What is an Atomic Number? Atoms of same element = same # protonsAtomic # = # of protonsNeutral atoms means the atomic # = protons = electrons (i.e., net charge = zero)
25 Practice Atomic Number Find the atomic number and name for the following elements:HScTaBhFSnUHydrogen 1Scandium 21Tatalum 73Bohrium 107Flourine 9Tin 50Uranium 92How many electrons does each of the listed elements have?
26 Atomic Mass Number Most atoms have protons and neutrons Atomic Mass # = protons + neutronsAtomic Mass = Atomic Number + neutronsHow can atoms of the same element have different mass #’s when they all MUST have the same atomic #?
27 Reminding YourselfWhich two types of subatomic particles are located in the nucleus?How does the mass of an electron compare with the mass of a proton?Why are atoms neutral?What force holds atoms together?
28 Isotopes Atoms of an element with different mass #’s Remember, the AN (# of protons) is ALWAYS the same# of neutrons is different from one isotope to another
29 Let’s Peer at H Isotopes . . . ProtiumDeuteriumTritiumWhat is the atomic number, atomic mass, and electrical charge for each?
30 How Common Are Different Isotopes? Some more than others (e.g., O has AM of 16 usually; about 0.2% have mass of 18)Some isotopes are unstable and decayHow can decayed isotopes form new/different isotopes of the same element (even though they are breaking apart)?
31 How Can You Show an Atom’s Atomic and Mass Numbers ClChemical symbol represents the elementAMN is written on topAN is written on bottomHow can you compute the number of neutrons?35 17
32 More About Atomic MassToo tiny 1 atom of F has mass (kg) of less than one trillionth of one billionth of one gramWhat do you think that number looks like? Write it down and compare with your neighbor11,000,000,000,000,000X1,000,000,000,000
33 Unified Atomic Mass Unit Describes the masses of atomsSI standard of measure for atomsA AMU = 1/12 mass of C-12 atomMass number = protons + neutrons (i.e., whole number)Atomic mass = mass of single atom of element (i.e., usually a decimal)
34 How’s Your Memory? What is the AN of most atoms of O? What is the AMN of most atoms of O?How many protons are in the nucleus of an atom of Cl?What unit do scientist use to measure the masses of atoms?
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