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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 Gold Mercury Chemists are interested in the nature of matter and how this is related to its atoms and molecules.

2 Nature 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)

3 Nature 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 FORMULA H2O C8H10N4O2 - caffeine

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

6 Copper atoms on silica surface. See CD-ROM Screen 1.4
Nature of Matter, cont’d An 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 1.4 Distance across = 1.8 nanometer (1.8 x 10-9 m)

7 Nature of Matter, cont’d
ATOMIC COMPOSITION Protons + electrical charge mass = x g relative mass = atomic mass units (amu) Electrons negative electrical charge relative mass = amu Neutrons no electrical charge mass = amu

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

9 ATOMS AND ELEMENTS To play the movies and simulations included, view the presentation in Slide Show Mode.

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

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 Mass Number (A) = # protons + # neutrons
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 n = 10 amu

16 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 10B 11B

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 Isotopes determined with a mass spectrometer

20 10B 11B 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 = (10 amu) (11 amu) = 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 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 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 g/mol. How many atoms in this piece of Mg? = 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 Reaction of potassium + H2O
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 What determines the colors of precious stones ?
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 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. 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 “Buckyballs” Graphite — layer structure of carbon atoms reflects physical properties. C60:buckminsterfullerene

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

45 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 P4O10, which then transforms into H3PO4

46 Group 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 Mexico Sulfur from a volcano

47 Group 7A:halogens F, Cl, Br, I, At

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

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.

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