PSC 4010

PSC 4010Nuclear Technology: A matter of Energy

PSC 4010: Chapter 2Goals:

_ SWBAT put the different atomic theories in a historical and technical context

_SWBAT compare the current simplified atomic model with all precedent models and theories

PSC 4010: Chapter 2What is a theory?An organized set of laws designed to show that a scientific system is valid. For this purpose, theories use scientific models

Theories can:_be supported by facts_be rejected by experimental evidence_sometimes take long to be proven true (or not)

PSC 4010: Chapter 2Brainstorm: What is a model?

A model is a physical representation of something we cannot see (even without visible proofs we can demonstrate the existence of objects and explain their nature)PSC 4010: Chapter 2

PSC 4010: Chapter 2A bit of history (pp. 2,3 2,7)

Ancient GreeksNaturalists (nature could work on its own, following laws and not controlled by gods)What is matter composed of?

PSC 4010: Chapter 2LeucippusInventor of AtomAtomos (Indivisible)Observing dust particles, concluded that matter is composed of infinitely small particles that could no longer be divided

PSC 4010: Chapter 2DemocritusDisciple of LeucippusDeveloped first Atomic TheoryMatter is discontinuous There are gaps between atoms. These always move and can combine together

PSC 4010: Chapter 2EmpedoclesTheory of four elementsMatter is continuous All substances are made of Water, Earth, Air and Fire

PSC 4010: Chapter 2AristotleTheory of four elements (as Empedocles)The four elements can combine to form other substances by the influence of Moisture, Dryness, Cold and Heat (diagram p. 2,5)

PSC 4010: Chapter 2Theory of four elements continued for about 2000 years until18th century, Water is discovered to be made of hydrogen and oxygen18th century, Air is discovered to be a mixture of many gases

PSC 4010: Chapter 2Matter is continuous ____Matter is made of very small particles ____Developed first atomic theory____Four elements combine to form new substances____Invented word Atom ____First to talk about 4 elements____Matter is discontinuous____

L: LeucippusD: DemocritusE: EmpedoclesA: AristotleELDALEDPSC 4010: Chapter 2

Purely theoretical ideas since they had no technical means of proving their hypothesesPSC 4010: Chapter 2

Uniform matter (no gaps)Tiny particles (atoms) with gaps between themMatter is composed of indivisible atomsMatter is discontinuousPSC 4010: Chapter 2What have we learned about the different atomic theories and their historical and technical context?

Industrial Revolution_The very small universe_The structure of matterWhat is matter composed of?_Matter is continuous, discontinuous, indivisible, four elementsAncient Greeks (Naturalists)_Development of thinkers and PhilosophersEnd of four elements theory_New discoveries (chemistry & electricity)PSC 4010: Chapter 2More history

Renaissance (14th to 17th century)Growing interest in physical world (geography and astronomy)Europe wanted to extend borders of known world and extend its influence to Africa and the OrientIncrement in international tradeDiscovery of New World (America)

PSC 4010: Chapter 2And then camethe Industrial Revolution

New discoveries (chemistry and electricity)Scientific world interested in the very small universe and the structure of matter

PSC 4010: Chapter 2Daltons model (pp. 2,10 2,14)

An element is a collection of identical atomsA compound is a combination of different atoms Different elements have different massesOrganized known elements according to their relative masses (compared to Hydrogen, the lightest, considered of unit value, e.g. = 1)His model did not include the presence of chargesPSC 4010: Chapter 2

Secondary IV Textbook (MELS) The Material World Chapter 1: Atoms and ElementsPSC 4010: Chapter 2

Leucippus & Democritus had done soDalton thought atoms were indivisibleDalton thought atoms of same element were identicalPSC 4010: Chapter 2Thomsons model (pp. 2,18 2,20)

Bringing a magnet near a cathode ray tube (flow of electrons between two electrodes in a vacuum), made the flow bentThis was a proof that atoms possess charged particlesHe called those particles Electrons, and decided they had negative chargeSince atoms are neutral, they must have positive charges, and also these charges should be in identical number with the negative ones

PSC 4010: Chapter 2Secondary IV Textbook (MELS) The Material World Chapter 1: Atoms and Elements

PSC 4010: Chapter 2

Dalton thought atoms were indivisible and had no charges. Thomsons model has a divisible atom (can be divided into positive and negative particles)The electron (negatively charged)Thomson though electrons were scattered throughout a positively charged sphere, thus neutrality was achieved (charged muffin)PSC 4010: Chapter 2Rutherfords model (pp. 2,20 2,23)

Bombarded a thin sheet of gold with fast moving alpha particles (positively charged, to be studied later)Gold can be stretched and made extremely thinProved that matter (atoms) consist mostly of empty space (Matter is discontinuous: Democritus)Almost all atomic mass is concentrated in a small nucleus with a very strong positive chargeThe positively charged particles in the nucleus were called ProtonsThe nucleus would be surrounded by a cloud of very light electrons

PSC 4010: Chapter 2

PSC 4010: Chapter 2

PSC 4010: Chapter 2

Most particles bombarded were not deflected_Positive: positive bombarded particles were repelled_Dense: positive bombarded particles bounced back_Compact: only a few of bombarded particles seemed strike nucleus

PSC 4010: Chapter 2

ProtonsPositiveNegative electrons would crash into the positive nucleus (Thomson-like model)PSC 4010: Chapter 2Bohrs model (pp. 2,23 2,24)

Added the idea of energy levels, where electrons revolve around the nucleus in fixed levels or shells

PSC 4010: Chapter 2

PSC 4010: Chapter 2Chadwicks model or the Simplified Atomic Model (pp. 2,24 2,30)

Tried to respond to the question: how could positively charged particles in the nucleus stay together and not repel?

Concluded that neutral particles must also be in the nucleus, between the protons, in order to separate them and thus decrease any force of repulsion. He called those neutral particles Neutrons

A much stronger force must therefore exist in the nucleus, operating at very small distances, to keep the nucleus from disintegrating. This is the nuclear force, and will be studied later in this module

PSC 4010: Chapter 2

PSC 4010: Chapter 2

NeutronNeutron must exist in order to keep the nucleus from disintegrating due to the electrostatic repulsions of positively charged protonsPSC 4010: Chapter 2What have we learned about the evolution of the Atomic Model?Daltons (solid indivisible balls, no charge, different masses)

Thomsons (positive nucleus, embedded with negative electrons)

Rutherfords (atoms are mostly empty space, most mass is found at nucleus, light electrons surround it)

Bohrs (electrons revolve around nucleus in fixed levels or shells)

PSC 4010: Chapter 2What is the new atomic model?

How are the other models added to it?

PSC 4010: Chapter 2Evolution of the atomic model:

New subatomic particles have been discovered (not part of this program)

Atoms are neutral, therefore # protons = # electrons

Protons and neutrons are very heavy (compared to electrons) and have similar masses

Electron configuration: arrangement of electrons around the nucleus of an atom (you must know the name of the first 20 elements of the Periodic Table for Chapter 3)

PSC 4010: Chapter 2Electron configuration: arrangement of electrons around the nucleus of an atom (you must know the name of the first 20 elements of the Periodic Table for Chapter 3)

For our purposes (20 first elements), each level has a maximum of:_First level: 2 electrons max_Second level: 8 electrons max_Third level: 8 electrons max

Examples:

Nitrogen (Atom. Num 7, so 7 protons, and also 7 electrons): 2e, 5eSilicon (Atom. Num 14, so 14 protons, and also 14 electrons): 2e, 8e, 4eCalcium (Atom. Num 20, so 20 protons, and also 20 electrons): 2e, 8e, 8e, 2e

PSC 4010: Chapter 2

PSC 4010: Chapter 2

PSC 4010: Chapter 2

PSC 4010: Chapter 2

PSC 4010: Chapter 2Practice Exercises for Chapter 2:

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