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Atoms and Elements:The Nature of Matter Chemists are interested in the nature of matter and how this is related to its atoms and molecules. Gold Mercury.

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Presentation on theme: "Atoms and Elements:The Nature of Matter Chemists are interested in the nature of matter and how this is related to its atoms and molecules. Gold Mercury."— Presentation transcript:

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

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

4 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 FORMULA H2OH2OH2OH2O C 8 H 10 N 4 O 2 - caffeine Nature of Matter, cont’d

5 STATES OF MATTER SOLIDS — have rigid shape, fixed volume. External shape can reflect the atomic and molecular arrangement.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.LIQUIDS — have no fixed shape and may not fill a container completely. –Not well understood. GASES — expand to fill their container.GASES — expand to fill their container. –Good theoretical understanding. Nature of Matter, cont’d

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

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

8 ATOMIC COMPOSITION ProtonsProtons –+ electrical charge –mass = x g –relative mass = atomic mass units (amu) ElectronsElectrons – negative electrical charge –relative mass = amu NeutronsNeutrons – no electrical charge –mass = amu Nature of Matter, cont’d

9 An atom consists of a nucleusnucleus –(of protons and neutrons) electrons in space about the nucleus.electrons in space about the nucleus. The Atom Electron cloud Nucleus

10 A TOMS AND E LEMENTS

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

12 ATOM COMPOSITION protons and neutrons in the nucleus.protons and neutrons in the nucleus. the number of electrons is equal to the number of protons.the number of electrons is equal to the number of protons. electrons in space around the nucleus.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.Atoms are extremely small: One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water. The atom is mostly empty space

13 The modern view of the atom was developed by Ernest Rutherford ( ). Screen 2.9

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

15 Atomic Weight This tells us the mass of one atom of an element relative to one atom of another element.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.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.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 measuredDefine one element as the standard against which all others are measured Standard = carbonStandard = carbon

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

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

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

19 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.

20 Masses of Isotopes determined with a mass spectrometer

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

22 Isotopes & Atomic Weight Because of the existence of isotopes, the mass of a collection of atoms has an average value.Because of the existence of isotopes, the mass of a collection of atoms has an average value. 6 Li = 7.5% abundant and 7 Li = 92.5% 6 Li = 7.5% abundant and 7 Li = 92.5% –Atomic weight of Li = ______________ 28 Si = 92.23%, 29 Si = 4.67%, 30 Si = 3.10% 28 Si = 92.23%, 29 Si = 4.67%, 30 Si = 3.10% –Atomic weight of Si = ______________

23 Counting Atoms Mg burns in air (O 2 ) to produce white magnesium oxide, MgO. How can we figure out how much oxide is produced from a given mass of Mg?

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

25 Particles in a Mole x Avogadro’s Number There is Avogadro’s number of particles in a mole of any substance. Amedeo Avogadro

26 Molar Mass 1 mol of 12 C = g of C = x atoms of C g of 12 C is its MOLAR MASS Taking into account all of the isotopes of C, the molar mass of C is g/mol

27 One-mole Amounts

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

29 Periodic Table Dmitri Mendeleev developed the modern periodic table. Argued that element properties are periodic functions of their “atomic weights”.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.We now know that element properties are periodic functions of their ATOMIC NUMBERS.

30 Periods in the Periodic Table

31 Regions of the Periodic Table

32 Element Abundance Fe C Al O Si

33 HydrogenHydrogen Shuttle main engines use H 2 and O 2 What was the cause of the Hindenburg fire while landing in New Jersey in May 1939 ?

34 Group 1A: Alkali Metals Cutting sodium metal Reaction of potassium + H 2 O Solids at room temperature, react with water What are the characteristic properties of a metal ?

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

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

37 Group 3A: B, Al, Ga, In, Tl Aluminum, the most abundant metal in the earth’s crust Boron halides BF 3 & BI 3

38 Gems & Minerals Sapphire: Al 2 O 3 with Fe 3+ or Ti 3+ impurity gives blue whereas V 3+ gives violet.Sapphire: Al 2 O 3 with Fe 3+ or Ti 3+ impurity gives blue whereas V 3+ gives violet. Ruby: Al 2 O 3 with Cr 3+ impurityRuby: Al 2 O 3 with Cr 3+ impurity What determines the colors of precious stones ?

39 Colors of Transition Metal Compounds Iron Cobalt Nickel CopperZinc

40 Relative Densities of the Elements

41 Transition Elements Lanthanides and actinides Iron in air gives iron(III) oxide 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.

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

43 Group 4A: C, Si, Ge, Sn, Pb Quartz, SiO 2 Diamond

44 Graphite — layer structure of carbon atoms reflects physical properties. Diamond “Buckyballs” Allotropes : distinct forms of nonmetals, also called allomorphic forms C 60 :buckminsterfullerene

45 Group 5A: N, P, As, Sb, Bi White and red phosphorus Ammonia, NH 3 How does nature break atmospheric N 2 and transform it into compounds such as chlorophyll, proteins and DNA ?

46 Phosphorus Phosphorus 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 P 4 O 10, which then transforms into H 3 PO 4

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

48 Group 7A:halogens F, Cl, Br, I, At salt

49 Group 8A: He, Ne, Ar, Kr, Xe, Rn Lighter than air balloons “Neon” signs XeOF 4 Gases at room temperature Until 1962 they were considered chemically unreactive

50 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.


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