Presentation on theme: "Atoms and Elements:The Nature of Matter"— Presentation transcript:
1Atoms and Elements:The Nature of Matter “It’s easier to break an atom than a prejudice” A. EinsteinGoldMercuryChemists are interested in the nature of matter and how this is related to its atoms and molecules.
2Nature of Matter, cont’d CHEMICAL COMPOUNDS are composed of atoms and so can be decomposed to those atoms.The red compound is composed of • nickel (Ni) (silver) • carbon (C) (black) • hydrogen (H) (white) • oxygen (O) (red) • nitrogen (N) (blue)
3Nature of Matter, cont’d A MOLECULE is the smallest unit of a compound that retains the chemical characteristics of the compound.Composition of molecules is given by a MOLECULAR FORMULAH2OC8H10N4O2 - caffeine
4Nature of Matter, cont’d STATES OF MATTERSOLIDS — have rigid shape, fixed volume. External shape can reflect the atomic and molecular arrangement.Reasonably well understood.LIQUIDS — have no fixed shape and may not fill a container completely.Not well understood.GASES — expand to fill their container.Good theoretical understanding.
5Kinetic Nature of Matter Nature of Matter, cont’dKinetic Nature of MatterMatter consists of atoms and molecules in motion.
6Copper atoms on silica surface. See CD-ROM Screen 1.4 Nature of Matter, cont’dAn atom is the smallest particle of an element that has the chemical properties of the element.Copper atoms on silica surface. See CD-ROM Screen 1.4Distance across = 1.8 nanometer (1.8 x 10-9 m)
7Nature of Matter, cont’d ATOMIC COMPOSITIONProtons+ electrical chargemass = x grelative mass = atomic mass units (amu)Electronsnegative electrical chargerelative mass = amuNeutronsno electrical chargemass = amu
8The Atom nucleus (of protons and neutrons) An atom consists of anucleus(of protons and neutrons)electrons in space about the nucleus.Electron cloudNucleus
9ATOMS AND ELEMENTSTo play the movies and simulations included, view the presentation in Slide Show Mode.
10RadioactivityOne of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ).She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.
11ATOM COMPOSITION The atom is mostly empty space protons and neutrons in the nucleus.the number of electrons is equal to the number of protons.electrons in space around the nucleus.Atoms are extremely small: One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water.
12The modern view of the atom was developed by Ernest Rutherford (1871-1937). Screen 2.9
13Atomic Number, ZAll atoms of the same element have the same number of protons in the nucleus, Z13Atomic numberAlAtom symbol26.981Atomic weight
14Atomic WeightThis tells us the mass of one atom of an element relative to one atom of another element.OR — the mass of 1000 atoms of one relative to 1000 atoms of another.For example, an O atom is approximately 16 times heavier than an H atom.Define one element as the standard against which all others are measuredStandard = carbon
15Mass Number, A Mass Number (A) = # protons + # neutrons C atom with 6 protons and 6 neutrons is the mass standard= 12 atomic mass unitsMass Number (A) = # protons + # neutronsA boron atom can have A = 5 p n = 10 amu
16IsotopesAtoms of the same element (same Z) but different mass number (A).Boron-10 (10B) has 5 p and 5 nBoron-11 (11B) has 5 p and 6 n10B11B
17Isotopes & Their UsesBone scans with radioactive technetium-99.
18Isotopes & Their UsesThe tritium content of ground water is used to discover the source of the water, for example, in municipal water or the source of the steam from a volcano.
19Masses of Isotopes determined with a mass spectrometer
2010B11BIsotopesBecause of the existence of isotopes, the mass of a collection of atoms has an average value.Average mass = ATOMIC WEIGHTBoron is 20% 10B and 80% 11B. That is, 11B is 80 percent abundant on earth.For boron atomic weight= (10 amu) (11 amu) = amu
21Isotopes & Atomic Weight Because of the existence of isotopes, the mass of a collection of atoms has an average value.6Li = 7.5% abundant and 7Li = 92.5%Atomic weight of Li = ______________28Si = 92.23%, 29Si = 4.67%, 30Si = 3.10%Atomic weight of Si = ______________
22Counting AtomsMg burns in air (O2) to produce white magnesium oxide, MgO.How can we figure out how much oxide is produced from a given mass of Mg?
23Counting AtomsChemistry is a quantitative science—we need a “counting unit.”MOLE1 mole is the amount of substance that contains as many particles (atoms, molecules) as C atoms in 12.0 g of 12C.
24Particles in a MoleAvogadro’s NumberAmedeo Avogadrox 1023There is Avogadro’s number of particles in a mole of any substance.
25Molar Mass 1 mol of 12C = 12.00 g of C = 6.022 x 1023 atoms of C 12.00 g of 12C is its MOLAR MASSTaking into account all of the isotopes of C, the molar mass of C is g/mol
27PROBLEM: What amount of Mg is represented by 0.200 g? How many atoms? Mg has a molar mass of g/mol.How many atoms in this piece of Mg?= x 1021 atoms Mg
28Periodic TableDmitri Mendeleev developed the modern periodic table. Argued that element properties are periodic functions of their “atomic weights”.We now know that element properties are periodic functions of their ATOMIC NUMBERS.
32Hydrogen Shuttle main engines use H2 and O2 What was the cause of the Hindenburg fire while landing in New Jersey in May 1939 ?
33Group 1A: Alkali Metals Reaction of potassium + H2O What are the characteristic properties of a metal ?Reaction of potassium + H2OCutting sodium metalSolids at room temperature, react with water
34Group 2A: Alkaline Earth Metals MagnesiumMagnesium oxideOccur naturally only in compounds,except for Bethey also react with water. Mg and Ca are the most abundant
35Calcium Carbonate—Limestone Champagne cave carved into chalk in FranceThe Appian Way, Italy
36Group 3A: B, Al, Ga, In, Tl Aluminum, the most abundant metal in the earth’s crustBoron halides BF3 & BI3
37What determines the colors of precious stones ? Gems & MineralsWhat determines the colors of precious stones ?Sapphire: Al2O3 with Fe3+ or Ti3+ impurity gives blue whereas V3+ gives violet.Ruby: Al2O3 with Cr3+ impurity
38Colors of Transition Metal Compounds NickelCobaltCopperZincIron
40Transition Elements Iron in air gives iron(III) oxide They are all metals, Ag, Au and Pt are the less reactiveStructural materials, paints, catalytic converters, batteriesThey play important biological roles, e.g., Fe.Lanthanides and actinidesIron in air gives iron(III) oxide
41Glenn Seaborg (1912-1999 ) Discovered 8 new elements. Only living person for whom an element was named.What is a synchrotron ? How does it work?
43Allotropes: distinct forms of nonmetals, also called allomorphic forms Diamond“Buckyballs”Graphite — layer structure of carbon atoms reflects physical properties.C60:buckminsterfullerene
44Group 5A: N, P, As, Sb, Bi Ammonia, NH3 White and red phosphorus How does nature break atmospheric N2 and transform it intocompounds such as chlorophyll, proteins and DNA ?Ammonia, NH3White and red phosphorus
45PhosphorusPhosphorus is essential to life, important constituent of bones and teeth, first isolated by Brandt from urine, Both white and red P ignite spontaneously in air to form P4O10, which then transforms into H3PO4
46Group 6A: O, S, Se, Te, Po Sulfur from a volcano What allotropes of oxygen do you know ?What is sulfuric acid most commonly used for ?Sulfuric acid dripping from snot-tite in cave in MexicoSulfur from a volcano
48Group 8A: He, Ne, Ar, Kr, Xe, Rn XeOF4 Gases at room temperature Until 1962 they were considered chemically unreactiveLighter than air balloons“Neon” signsXeOF4
49Summary Historical experiments that motivated the development of the modern view of matter (Thompson, Rutherford, M. Curie).Description of elementary particles(electrons, protons, neutrons).Isotopes, Atomic number (Z), Mass number (A), Atomic Weight.Molar mass, Avogadro’s number.Periodic Table, groups, periods, metals, metalloids, nonmetals, halogens, noble gases, transition elements.