The History of the Atom

Warm Up10/19/12How long have people been interested in understanding matter and its structure?Thousands of yearsHundreds of yearsA few yearsNever1History of Atomic Structure

2What is an atom?The smallest particle of an element.Atoms are so small that we cannot even see them with a microscope.How do scientists know what they look like or how they are made?

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AristotleDemocritushttp://www.youtube.com/watch?v=lY-Thmrt1Ts4Ancient PhilosophyWho: Aristotle, DemocritusWhen: More than 2000 years agoWhere: GreeceWhat: Aristotle believed in 4 elements: Earth, Air, Fire, and Water. Democritus believed that matter was made of small particles that could not be divided. He named them atoms meaning uncut or indivisible.Why: Aristotle and Democritus used observation and inference to explain the existence of everything.

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AlchemistsWho: European ScientistsWhen: 800 900 years agoWhere: EuropeWhat: Their work developed into what is now modern chemistry.Why: Trying to change ordinary materials into gold.

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Alchemic Symbols7Becquerel and CurieHenri Becquerel(1896)-- While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very penetrating rays.

Marie Curie(1898)--Studied uranium and thorium and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium.

8Lavoisier elements combine to form compounds.

ProustLaw of Definite ProportionsThe mass of elements of reactants equals the mass of elements of products.9Particle TheoryWho: John DaltonWhen: 1808Where: EnglandWhat: Described atoms as tiny particles that could not be divided. Thought each element was made of its own kind of atom.Why: Building on the ideas of Democritus in ancient Greece.

10John DaltonThe Atomic TheoryAll elements are composed of atoms.All atoms of the same element are the same, but different from other elements. They have same size, mass and properties.Compounds contain atoms of more than one element, combined in whole number ratios.Compounds form when atoms join, separate, or rearrange.

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John Dalton12Discovery of ElectronsWho: J. J. ThompsonWhen: 1897Where: EnglandWhat: Thompson discovered that electrons were smaller particles of an atom and were negatively charged.Why: Thompson knew atoms were neutrally charged, but couldnt find the positive particle.

13J. J. ThomsonFirst to show atoms are made of subatomic particles.Plum pudding model or chocolate chip ice cream model. Pudding or ice cream is positive charged mass o f matter and plums or chocolate chips are the negative charges evenly scattered throughout the atom.Used an electric current and the cathode ray tube to learn more about atoms.

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J. J. Thompson15Atomic Structure IWho: Ernest RutherfordWhen: 1911Where: EnglandWhat: Conducted an experiment to isolate the positive particles in an atom. Decided that the atoms were mostly empty space, but had a dense central core.Why: He knew that atoms had positive and negative particles, but could not decide how they were arranged.

16RutherfordThe atom is mostly empty space. All of the positive charge is located in the center of the atom in the nucleus. Electrons move randomly in the space around the nucleus.Used the gold foil experiment.

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

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Ernest Rutherford18ChadwickProtons and neutrons in nucleus.Protons positiveNeutrons-neutralElectrons-negativeProton mass = neutron mass; electrons much smaller19Atomic Structure IIWho: Niels BohrWhen: 1913Where: EnglandWhat: Proposed that electrons traveled in fixed paths around the nucleus. Scientists still use the Bohr model to show the number of electrons in each orbit around the nucleus. (energy levels)Why: Bohr was trying to show why the negative electrons were not sucked into the nucleus of the atom.

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Niels Bohr21Modern Model/Wave ModelShrodingerElectron Cloud ModelUses mathematical model to describe the certainty of finding an electron at a certain location on the electron cloud.The electron cloud is a visual model of the most likely locations for the electrons. Where the cloud is denser, there is more probability of finding an electron.An electron can move from one energy level to another when the atom gains or loses energy.

22Electron Cloud ModelElectrons travel around the nucleus in random orbits.Scientists cannot predict where they will be at any given moment.Electrons travel so fast, they appear to form a cloud around the nucleus.23

Electron Cloud Model24http://www.youtube.com/watch?v=wJ2e-uPmdYg

Atomic Theory Song:http://www.youtube.com/watch?v=vUzTQWn-wfE

25Atomic OrbitalsAn orbital is a region of space around the nucleus where an electron is likely to be found. An electron cloud is a good approximation of how electrons behave in their orbitals.Each orbital can contain 2 electrons.

Energy LevelNumber of OrbitalsMaximum Number of Electrons1 (s)122 (s, p)483 (s p d)9184 (s p d f)163226IsotopesIsotopes can be shown in several ways.Symbol-Atomic MassH-1 (P=__, E=__, N=__)H-2 (P=__, E=__, N=__)H-3 (P=__, E=__, N=__)

It can also be shown:27History of the Periodic TableMendeleev- Father of the Periodic Table; Arranged table according to increasing mass.Moseley- Improved the table by arranging it according to atomic number (number of protons). There are a few places on the chart where the mass decreases.Seaborg-pulled out the f block.

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29Arrangement of the Periodic TableElements are arranged by atomic number (number of protons).Each row on the periodic table is a period.Each column on the periodic table is a group.Similar electron configurations.Similar chemical properties.30Classes of ElementsThere are many different ways to classify elements.State of matterSolidsblack symbolLiquidblue symbolGasred symbolOccurrence in natureElements that do not occur naturallywhite symbolGeneral propertiesMetalNonmetalMetalloid31MetalsThe majority of the elements on the periodic table.Solids (except Hg)Good conductors of heat and electricityMalleable- can be hammered into sheetsDuctile- can be drawn into wiresHave luster (shiny)Found to the left of the stairstep.

32Transition MetalsMetals in groups 3-12.Form a bridge between the elements on the left and right sides of the table.Among the first discovered (Au, Ag, Cu)They form compounds with distinctive colors.33NonmetalsGenerally have properties opposite of metals.Poor conductors of heat and electricity.Nonmetals have low boiling pointsmany nonmetals are gases at room temperature.Brittle solids (will shatter if hit with a hammer) or gases (b/c low boiling points)

34MetalloidLocated between metals and nonmetals---touch the stairstep.Have some properties of metals and some of nonmetals.A metalloids ability to conduct electric current varies with temperature.Si and Ge are good insulators at low temperatures, but good conductors at high temperatures.Semiconductorsused in computer chips.

35As you move across the period, from left to right, the elements become less metallic and more nonmetallic in their properties.

Elements in a group have similar properties because they have the same number of valence electrons. They wont be identical because they have different number of energy levels.

36FamiliesAlkali MetalsAlkaline Earth MetalsTransition MetalsBoron GroupCarbon GroupNitrogen GroupOxygen GroupHalogensNoble Gases37Alkali MetalsThey have one outer (valence) electrons so they are very reactive.They are only found as compounds in naturebecause they are so reactive.Reactivity increases as you move down the group.Ex. SodiumStored under oil b/c so reactiveMakes NaClVideo or Na reactivity

38Alkaline Earth MetalsHave 2 valence electrons.Mg, Ca, Be39The Boron and Carbon FamiliesBoronAluminum is the most abundant metal in the Earths crust.Bauxite is made from Al and O.

Carbon GroupExcept for water, most of the compounds in your body contain carbon.Si is second most abundant element in Earths crust.

40Nitrogen groupN and P in fertilizerOxygen groupO most abundant element in Earths crust.HalogensThey all have similar chemical properties.. Very, very reactive.Noble gases- colorless, odorless, and extremely unreactive.41