Presentation on theme: "Unit II : Atoms, Molecules, Ions and Nuclear Chemistry"— Presentation transcript:
1Unit II : Atoms, Molecules, Ions and Nuclear Chemistry
2Early History of Chemistry Before 16th CenturyAlchemy: Attempts (scientific or otherwise) to change cheap metals into gold17th CenturyRobert Boyle: First “chemist” to perform quantitative experiments18th CenturyGeorge Stahl: Phlogiston flows out of a burning material.Joseph Priestley: Discovers oxygen gas, “dephlogisticated air.”
3Law of Conservation of Mass Discovered by Antoine LavoisierMass is neither created nor destroyedCombustion involves oxygen, not phlogiston
4Law of Definite Proportions Sometimes called the law of constant compositionJohn Proust (1799)A given compound always contains exactly the same proportion of elements by mass.Carbon tetrachloride is always 1 atom carbon per 4 atoms chlorine.
5Law of Multiple Proportions When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.The ratio of the masses of oxygen in H2O and H2O2 will be a small whole number (“2”).
6Dalton’s Atomic Theory Each element is made up of tiny particles called atoms.The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways.Chemical compounds are formed when atoms combine with each other. A given compound always has the same relative numbers and types of atoms.Chemical reactions involve reorganization of the atoms - changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.
7Avagadro’s Hypothesis (1811) At the same temperature and pressure, equal volumes of different gases contain the same number of particles.5 liters of oxygen5 liters of nitrogenSAME NUMBER OF PARTICLES
8Chemical Symbols Co Cu He H The chemical symbols used today were developed by Jons Jakob Berzelius.They consist of one or two letters.The first letter is always capitalized.The second, if there is one, is never capitalized. The second letter is often a letter prominent in the pronunciation.Co Cu He H
9Early Experiments to Characterize the Atom DemocritisDaltonThomsonRutherfordBohrSchrodinger
10Cathode RayStreams of negatively charged particles were found to emanate fromcathode tubes.J. J. Thompson is credited with their discovery (1897).
11Deflection of Cathode Ray by an Applied Electric Field
12Rutherford Gold Foil Experiment Ernest Rutherford shot particles at a thin sheet of gold foil and observed the pattern of scatter of the particles.
13Rutherford Gold Foil Experiment Expected results if Thomson’s Model was correctActual results
14Summary of Atom Democritis - first idea of the atom Dalton - ~1807 Atomic Theory (atom = ball)Thomson - Experiment with Cathode RayDiscovered the electron“Plum pudding model”Rutherford - Gold Foil ExperimentAtom is mostly empty space with a dense, positively charged nucleusBohr - “Solar System”Schrodinger - Quantum Mechanical Model
15Modern View of Atomic Structure The atom contains 3 types of subatomic particles:ElectronsNegatively charged, found outside the nucleus… very small mass… would take ~2000 electrons to equal the mass of 1 of the other subatomic particlesProtonsPositively charged, found in the nucleusNeutronsFound in the nucleus… like a proton but with no charge
16Subatomic Particle Summary Mass (g)ChargeAtomic Mass ScaleRelative MassRelative ChargeProton (p+)1.6726x10-24+1.602x camu1+1Neutron (n0)amuElectron (e-)9.109 x 10-27-1.602x c5.486 x amu1/1836-1
17Useful Units Atomic Diameter:10-10m (1 Å) = 100 pm = 1x10-8cm Nuclear Diameter: 10-13cm1 amu (atomic mass unit) = x10-24 kgBased off of C-12… relative mass of O w/ 8 protons and 8 neutrons is1 picometer (pm) = 1 x mNOTE:Heaviest atom has a mass of only 4.8x10-22g and a diameter of only 5x10-10mBiggest atom is 240 amu and is 50 Å across.Typical C-C bond length 154 pm (1.54 Å)Molecular models are 1 Å /inch or about 0.4 Å /cm
18K Atomic Number A = Z + N 39 19 Element Symbol A = mass number = number of protons + number of neutronsK39Element Symbol19Z = atomic number = number of protonsA = Z + NMass number = # p+ + # n0
19Isotopes Isotopes are atoms of the same element with different masses. Isotopes have different numbers of neutrons.Carbon has two natural isotopes: 12C and 13CHow does this change things?
20IsotopesOn the periodic table the given atomic mass is the AVERAGE massWe use percentage to help with this math.For Carbon, there is 98.89% 12C and 1.11% of 13CNow what?12 (mass of 12C) x =13 (mass of 13C) x ==
21IsotopesOn the periodic table the given atomic mass is the AVERAGE massWe use percentage to help with this math.For Carbon, there is 98.89% 12C and 1.11% of 13C
22Mass SpectrometerUsed to experimentally determine mass and percent abundances of isotopes
24PeriodicityWhen one looks at the chemical properties of elements, one notices a repeating pattern of reactivities.
25The Periodic Table1869- Dmiti Mendeleev organized 1st periodic table by lining elements up in horizontal rows in order of increasing atomic weightLeft spaces when an element was not known but should exist and have properties similar to the element about it in his table.Periodicity – periodic repetition of the properties of elements1913- H.G.J. Moseley organized elements according to increasing atomic numberLaw of chemical periodicityThe properties of the elements are periodicfunctions of atomic numbers.
26Features of the Periodic Table Vertical Columns: Groups or FamiliesA and B groups. “A” main group, “B” transition elementsHorizontal Rows: called periodsPeriodic Law: when the elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties
27Metals ~80% of all elements are metals High electrical conductivity and have a high luster when cleanedDuctile (can be made into wires) and MalleableCan form alloysAre solid at room temperature except for one… which one is it?
28Nonmetals Generally nonlustrous… which means not shiny Generally poor conductors of electricityWith the exceptions of carbon (graphite), none conduct electricityAllotropesA particular element can often exist in several different formsCarbon as graphite or diamond… oxygen as O2 or O3 (ozone)
30Overview of Groups Group 1A Group 2A Alkali Metals Metals, solid at room temp, and VERY REACTIVEOnly found in nature combined in compoundsGroup 2AAlkaline Earth MetalsMetals, solid at room temp, and also only found in nature in compoundsExcept for Be, all react with water to produce alkaline solutions
31Overview of Groups Group 7A Group 8A Halogens All exist in diatomic moleculesCombine violently with alkali metals to form saltsGroup 8ANoble Gases (Inert Gases)Least reactive elementsAll are gases
32Overview of Groups Group B Metals (Groups 3-12): Transition Metals & Inner Transition MetalsLanthanides- shiny metals similar in reactivity to alkaline earth metalsActinides- unique in nuclear structures – nuclei are unstable and therefore radioactiveInner Transitions Metals – rare-earth metals
34Chemical FormulasThe subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound.Molecular compounds are composed of molecules and almost always contain only nonmetals.
35Chemical Formulas: Diatomic Molecules These 7 elements occur naturally as diatomic molecules
36Types of Formulas Molecular Formula – CH4 Structural Formula Ball and Stick ModelSpace-Filling Model
37Types of Formulas Molecular Formula Empirical Formula Exact number of each type of atomC6H12O6Empirical FormulaLowest whole number ratio of each type of atomCH2O