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Atoms and Elements:The Nature of Matter

Atoms and Elements:The Nature of Matter

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Atoms and Elements:The Nature of Matter

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  1. Atoms and Elements:The Nature of Matter “It’s easier to break an atom than a prejudice” A. Einstein Chemists are interested in the nature of matter and how this is related to its atoms and molecules. Gold Mercury

  2. Nature of Matter, cont’d The red compound is composed of• nickel (Ni) (silver)• carbon (C) (black)• hydrogen (H) (white)• oxygen (O) (red)• nitrogen (N) (blue) CHEMICAL COMPOUNDSare composed of atoms and so can be decomposed to those atoms.

  3. Nature of Matter, cont’d A MOLECULEis the smallest unit of a compound that retains the chemical characteristics of the compound. Composition of molecules is given by aMOLECULAR FORMULA C8H10N4O2 - caffeine H2O

  4. Nature of Matter, cont’d STATES OF MATTER • SOLIDS— 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.

  5. Nature of Matter, cont’d Kinetic Nature of Matter Matter consists of atoms and molecules in motion.

  6. Nature of Matter, cont’d Copper atoms on silica surface.See CD-ROM Screen 1.4 • An atomis the smallest particle of an element that has the chemical properties of the element. Distance across = 1.8 nanometer (1.8 x 10-9 m)

  7. Nature of Matter, cont’d ATOMIC COMPOSITION • Protons • + electrical charge • mass = 1.672623 x 10-24 g • relative mass = 1.007 atomic mass units (amu) • Electrons • negative electrical charge • relative mass = 0.0005 amu • Neutrons • no electrical charge • mass = 1.009 amu

  8. Electron cloud Nucleus The Atom An atom consists of a • nucleus • (of protonsand neutrons) • electrons in space about the nucleus.


  10. Radioactivity • One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934). • She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

  11. ATOM 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.

  12. The modern view of the atom was developed by Ernest Rutherford(1871-1937). Screen 2.9

  13. Atomic number Atom symbol Atomic weight Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z 13 Al 26.981

  14. Atomic Weight • This 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 measured • Standard = carbon

  15. Mass Number, A • C atom with 6 protons and 6 neutrons is the mass standard • = 12 atomic mass units • Mass Number (A) = # protons + # neutrons • A boron atom can have A = 5 p + 5 n = 10 amu

  16. 11B 10B Isotopes • Atoms of the same element (same Z) but different mass number (A). • Boron-10 (10B) has 5 p and 5 n • Boron-11 (11B) has 5 p and 6 n

  17. Isotopes & Their Uses Bone scans with radioactive technetium-99.

  18. Isotopes & Their Uses The 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.

  19. Masses of Isotopesdetermined with a mass spectrometer

  20. 11B 10B Isotopes • Because of the existence of isotopes, the mass of a collection of atoms has an average value. • Average mass = ATOMIC WEIGHT • Boron is 20% 10B and 80% 11B. That is, 11B is 80 percent abundant on earth. • For boron atomic weight = 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu

  21. Isotopes & 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 = ______________

  22. Counting Atoms Mg 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?

  23. Counting Atoms Chemistry is a quantitative science—we need a “counting unit.” MOLE 1 mole is the amount of substance that contains as many particles (atoms, molecules) as C atoms in 12.0 g of 12C.

  24. Particles in a Mole Avogadro’s Number Amedeo Avogadro 1776-1856 6.02214199 x 1023 There is Avogadro’s number of particles in a mole of any substance.

  25. Molar 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 MASS Taking into account all of the isotopes of C, the molar mass of C is 12.011 g/mol

  26. One-mole Amounts

  27. PROBLEM: What amount of Mg is represented by 0.200 g? How many atoms? Mg has a molar mass of 24.3050 g/mol. How many atoms in this piece of Mg? = 4.95 x 1021 atoms Mg

  28. Periodic Table • Dmitri 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.

  29. Periods in the Periodic Table

  30. Regions of the Periodic Table

  31. Element Abundance C O Al Si Fe

  32. Hydrogen Shuttle main engines use H2 and O2 What was the cause of the Hindenburg fire while landing in New Jersey in May 1939 ?

  33. Group 1A: Alkali Metals What are the characteristic properties of a metal ? Reaction of potassium + H2O Cutting sodium metal Solids at room temperature, react with water

  34. Group 2A: Alkaline Earth Metals Magnesium Magnesium oxide Occur naturally only in compounds,except for Be they also react with water. Mg and Ca are the most abundant

  35. Calcium Carbonate—Limestone Champagne cave carved into chalk in France The Appian Way, Italy

  36. Group 3A: B,Al, Ga, In, Tl Aluminum, the most abundant metal in the earth’s crust Boron halides BF3 & BI3

  37. Gems & Minerals What determines the colors of precious stones ? • Sapphire: Al2O3 with Fe3+ or Ti3+ impurity gives blue whereas V3+ gives violet. • Ruby: Al2O3 with Cr3+ impurity

  38. Colors of Transition Metal Compounds Nickel Cobalt Copper Zinc Iron

  39. Relative Densities of the Elements

  40. Transition Elements They are all metals, Ag, Au and Pt are the less reactive Structural materials, paints, catalytic converters, batteries They play important biological roles, e.g., Fe. Lanthanides and actinides Iron in air gives iron(III) oxide

  41. Glenn Seaborg(1912-1999 ) • Discovered 8 new elements. • Only living person for whom an element was named. What is a synchrotron ? How does it work?

  42. Group 4A: C, Si, Ge, Sn, Pb Quartz, SiO2 Diamond

  43. Allotropes: distinct forms of nonmetals, also called allomorphic forms Diamond Graphite — layer structure of carbon atoms reflects physical properties. “Buckyballs” C60:buckminsterfullerene

  44. Group 5A: N, P, As, Sb, Bi How does nature break atmospheric N2 and transform it into compounds such as chlorophyll, proteins and DNA ? White and red phosphorus Ammonia, NH3

  45. Phosphorus • Phosphorus is essential to life, important constituent of bones and teeth, first isolated by Brandt from urine, 1669. Both white and red P ignite spontaneously in air to form P4O10, which then transforms into H3PO4

  46. Group 6A: O, S, Se, Te, Po What allotropes of oxygen do you know ? What is sulfuric acid most commonly used for ? Sulfuric acid dripping from snot-tite in cave in Mexico Sulfur from a volcano

  47. Group 7A:halogensF, Cl, Br, I, At salt

  48. XeOF4 Group 8A: He, Ne, Ar, Kr, Xe, Rn Gases at room temperature Until 1962 they were considered chemically unreactive • Lighter than air balloons • “Neon” signs

  49. Summary • 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.