Presentation on theme: "The Atom, The History, and The Periodic Table (Chemical Naming and Formula Writing) Unit #3 Part I Chemistry."— Presentation transcript:
1The Atom, The History, and The Periodic Table (Chemical Naming and Formula Writing) Unit #3Part IChemistry
2Theories Involving Matter and Atoms DemocritusGreek400 B.C. – Greeks: “all matter iscomposed of 4 fundamentalsubstances”Earth, air (wind), water & fireDemocritus: “matter is composedof small, indivisible parts,” (Greek –“atomos”)No experiments to test; no definitive conclusionFirst scientist to discover the idea of an atom
3Alchemy (next 2000 years) Mixture of science and mysticism. Lab procedures were developed, but alchemists did not perform controlled experiments like true scientists.
4Theories cont. Aristotle Greek Rejected the idea of atoms Expanded on idea of 4elementsReasoning from logic & observationAlso in line with religion
5Theories cont. Lavoisier French chemist “Father of Modern Chemistry” Experimented and measured the masses of reactants and products of various reactionsLaw of Conservation of Matter
6Theories cont. Proust French chemist Showed that a given compound always contains the same proportion of elements by massLaw of Definite Proportions
7Theories cont. John Dalton (1803) English schoolteacher Thought about atoms as particles that might compose elementsBilliard Ball Modelatom is a uniform, solid sphereElements combine in the ratio of small whole numbersLaw of Multiple Proportions
8John Dalton Dalton’s Four Postulates 1. Elements are composed of small indivisible particles called atoms.2. Atoms of the same element are identical. Atoms of different elements are different.3. Atoms of different elements combine together in simple proportions to create a compound.4. In a chemical reaction, atoms are rearranged, but not changed.
9Henri Becquerel (1896) Discovered radioactivity Three types: spontaneous emission of radiation from the nucleusThree types:alpha () - positivebeta () - negativegamma () - neutral
10J. J. Thomson (1903) Cathode Ray Tube Experiments Discovered Electrons beam of negative particlesDiscovered Electronsnegative particles within the atomPlum-pudding Model
11J. J. Thomson (1903) Plum-pudding Model positive sphere (pudding) with negative electrons (plums) dispersed throughout
12Ernest Rutherford (1911) Gold Foil Experiment Discovered the nucleus dense, positive charge in the center of the atomNuclear Model
13Ernest Rutherford (1911) Nuclear Model dense, positive nucleus surrounded by negative electrons
14Niels Bohr (1913) Bright-Line Spectrum Energy Levels Planetary Model tried to explain presence of specific colors in hydrogen’s spectrumEnergy Levelselectrons can only exist in specific energy statesPlanetary Model
15Niels Bohr (1913) Bright-line spectrum Planetary Model electrons move in circular orbits within specific energy levels
16Erwin Schrödinger (1926) Quantum mechanics Electron cloud model electrons can only exist in specified energy statesElectron cloud modelorbital: region around the nucleus where e- are likely to be found
17Electron Cloud Model (orbital) Erwin Schrödinger (1926)Electron Cloud Model (orbital)dots represent probability of finding an e- not actual electrons
18James Chadwick (1932) Discovered neutrons Joliot-Curie Experiments neutral particles in the nucleus of an atomJoliot-Curie Experimentsbased his theory on their experimental evidence
19revision of Rutherford’s Nuclear Model James Chadwick (1932)Neutron Modelrevision of Rutherford’s Nuclear Model
20Atoms Best current representation of the atom is a charged-cloud Smallest particle of an element that retains its propertiesElectrically neutral; # Protons = # electrons Parts of an atomNucleus (contains both protons and neutrons)Electron Cloud (contains electrons)
21Parts of an Atom Nucleus Small, dense center of positive charge. ProtonsPositively charged particles within the nucleusNeutronsParticles within the nucleus with no chargeAbout the same mass as protons
22Parts of an Atom cont. Electron Cloud Empty Space Holds electrons, which are densely packedNegatively charged particles found outside the nucleusMuch smaller than protons and neutronsProton/neutron mass = 1.67 x gElectron mass = 9.11 x gMore about electron behavior later
23Picture of an atome-ElectronsNeutronsp+NucleusProtonsno
24Atoms and ElementsWhat is the difference between an element and an atom?An atom is a single example of an element.An element is the collective term for many atoms of a single substance.
25Periodic Table of Elements Structure Listed in order of inc. atomic #Columns = Families or GROUPSHave similar chemical propertiesReferred to by the number and letter (A or B) over the columnMany have special namesRows = PERIODSContains info on physical properties(i.e. mp, bp, density, physical states, etc)
26Element Characteristic Each square usually containsElement nameElement symbolAtomic numberThe number of protonsSymbolized at “Z”Atomic mass or mass numberAtomic mass: decimal mole weight= to the average mass numbers of all isotopesMass number: rounded mole weightMass number: The sum of the number of the protons and the number of neutronsState of matter (usually)
27Short Handing Element Characteristics SymbolizingAzXA = mass # (NO DECIMALS!)Z = atomic # (# of protons & electrons)X = symbol of the element
28IsotopesIsotopesAtoms with the same number of protons but a different number of neutronsAtoms of the same element have the same atomic number but different mass numbers
31Isotopes cont.The diagram shows three oxygen isotopes. Each nucleus has eight protons (gray) and eight, nine, or ten neutrons (green).
32Oxidation Numbers Indicate the charge on the ion Found on the periodic tableCommon oxidation numbers are given in additional tableNote:Group 8 elements do not form ions; No ox #Transition metals have multiple ox #’s
33Valence Electrons Electrons in the outer most shell The electrons on an atom that can be gained or lost in a chemical reactionMore on this to come with Electron Configurations….
34Alkali Metals Group IA (except H) Li, Na, K, Rb, Cs, Fr Soft, gray metalsVery reactiveEspecially with waterReact with water to form bases“Alkali” = basic
35Alkali Metals cont. Why are they so reactive? One electron in their outer shellOnly 1 electron away from a full outer shellWant to lose that electron: easily reactSo reactive – don’t occur as free elements
36Interesting Tidbits Li – used as depression medication Cs – used in atomic clocksFr – predicted by Mendeleev in 1870s; discovered in 1939Less than 1 oz. of Fr exists at any given time
37Alkali Earth Metals Group IIA Be, Mg, Ca, Sr, Ba, Ra Shiny, silvery-white metalsHarder and denser than Group IADistributed in rock formationsReactive but not as reactive as Group IA2 outer electronsWant to lose 2 to have a complete outer shell+2 oxidation number
38Interesting Tidbits Used in pyrotechnics and fireworks Mg – white; Sr – red; Ba – green
39Calcium Widely distributed as limestone Important biologically for bones and teethCompounds of Calcium- CaCO3 = limestone]- CaO = “lime” or “quicklime”- Ca(OH)2 = “limewater”; treat antacid
40Nobel Gases He, Ne, Ar, Kr, Xe, & Rn Group VIIIAHe, Ne, Ar, Kr, Xe, & RnAka “Inert Gases” b/c they are unreactiveAka “Rare Gases” b/c they are very rare on EarthColorless, tasteless, odorless
41Nobel Gases cont. Why are they unreactive? Their outer shells are full Recall: the outer shell electrons are the ones involved in bondingWhen the outer shells are full, these electrons can’t bond and, therefore, react with other elementsUsed in:LightingFill light bulbs, neon lights, black lights, flashlight bulbs, strobe lights, headlights, etc.
42Halogens F, Cl, Br, I, At Non-metals Group VIIAF, Cl, Br, I, AtNon-metals- Exist in all 3 states at room temperature:* Solid: I, At* Liquid: Br* Gas: F, ClVery reactiveMost often, bond with metalsDiatomic (F2, Cl2, etc.)
43Halogens cont. Why are the halogens diatomic? 1 electron away from a full outer shellToo reactive/unstable by itselfBonds with another atom so both have 8Dot diagramsWhat is the mole weight of chlorine gas?Which is more reactive, F2 or Cl2?F2
44Transition Metals Middle section of the periodic table Exhibit metallic propertiesDuctileMalleableGood conductors of heat and electricitySilvery luster (except Cu and Au)
45Ions Atoms that have a positive or negative charge To become an ion, an atom gains or loses electronsCation = positively charged ion;Lose electron(s)Metals form positive ionsAnion = negatively charged ion;Gain electron(s)
46Polyatomic IonsDef: tightly bound groups of atoms that behave as a unit and carry a chargeIon composed of more than one atomList of common polyatomic ionsEx:SO4-2NO ** Must memorize theseCO polyatomic ions! **PO4-3OH-1C2H3O2-1NH4+1