Dr. S. M. Condren

Chapter 2

Atoms and Elements

Dr. S. M. Condren

Dalton’s Atomic Theory

Postulates

• proposed in 1803

• know for first exam

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Dalton’s Atomic Theory

Postulate 1

• An element is composed of tiny particles called atoms.

• All atoms of a given element show the same chemical properties.

Dr. S. M. Condren

Dalton’s Atomic Theory

Postulate 2• Atoms of different elements have

different properties.

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Dalton’s Atomic Theory

Postulate 3

• Compounds are formed when atoms of two or more elements combine.

• In a given compound, the relative number of atoms of each kind are definite and constant.

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Dalton’s Atomic Theory

Postulate 4

• In an ordinary chemical reaction, no atom of any element disappears or is changed into an atom of another element.

• Chemical reactions involve changing the way in which the atoms are joined together.

Dr. S. M. Condren

Structure of the Atom

Composed of:• protons• neutrons• electrons

• protons– found in nucleus– relative charge of +1– relative mass of 1.0073 amu

Dr. S. M. Condren

Structure of the Atom

Composed of:• protons• neutrons• electrons

• neutrons– found in nucleus– neutral charge– relative mass of 1.0087 amu

Dr. S. M. Condren

Structure of the Atom

Composed of:• protons• neutrons• electrons

• electrons– found in electron cloud– relative charge of -1– relative mass of 0.00055 amu

Dr. S. M. Condren

ATOM COMPOSITION

•protons and neutrons in the nucleus.

•the number of electrons is equal to the number of protons in a neutral atom.

•electrons in space around the nucleus.

•extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water.

The atom is mostlyempty space

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Radioactivity

• Alpha – helium-4 nucleus

• Ra226 Rn222 + He4()

• Beta – high energy electron

• U239 Np239 + -1

• Gamma – energy resulting from transitions from one nuclear energy level to another

• Ni60* Ni60 +

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Penetrations ofRadioactive Emissions

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Isotopes & Their UsesHeart scans with radioactive technetium-99.

9943Tc

Emits gamma rays

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The modern view of the atom was developed by The modern view of the atom was developed by

Ernest Rutherford (1871-1937).(1871-1937).

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Rutherford’s Model of the Atom

• atom is composed mainly of vacant space

• all the positive charge and most of the mass is in a small area called the nucleus

• electrons are in the electron cloud surrounding the nucleus

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Nucleus

If nucleus is 1” The atom would be 1.5 miles in diameter

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Ions• Ion

– electrostatically charged atom or group of atoms

• cations– positive ions

• anions– negative ions

• ionic compounds– combination of cations and anions– zero net charge

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Atomic number, Z• the number of protons in the nucleus

• the number of electrons in a neutral atom

• the integer on the periodic table for each element

1313

AlAl

26.98126.981

Atomic numberAtomic number

Atom symbolAtom symbol

Atomic weightAtomic weight

Dr. S. M. Condren

Dr. S. M. Condren

Imaging

Dr. S. M. Condren

Which best represents the poles?

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Quantum Corral

http://www.almaden.ibm.com/vis/stm/corral.html

Dr. S. M. Condren

Mass Number,, A• C atom with 6 protons and 6

neutrons is the mass standard

• = 12 atomic mass units (u)

• Mass Number (A)= # protons + # neutrons

• A boron atom can have A = 5 p + 5 n = 10 u

A

Z

10

5B

A

Z

10

5B

Dr. S. M. Condren

Isotopes

• atoms of the same element which differ in the number of neutrons in the nucleus

• designated by mass number

Dr. S. M. Condren

Isotopes of Hydrogen H-1, 1H, protium

• 1 proton and no neutrons in nucleus

• only isotope of any element containing no neutrons in the nucleus

• most common isotope of hydrogen

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Isotopes of Hydrogen H-2 or D, 2H, deuterium

• 1 proton and 1 neutron in nucleus

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Isotopes of Hydrogen H-3 or T, 3H, tritium

• 1 proton and 2 neutrons in nucleus

radioactive

electron antineutrino

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The radioactive isotope 14C has how many neutrons?

6, 8, other

Dr. S. M. Condren

The identity of an element is determined by the number of which particle?

protons, neutrons, electrons

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Mass Spectrometer

a simulation is available athttp://www.colby.edu/chemistry/OChem/DEMOS/MassSpec.html

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Mass spectrum of C6H5Br

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Atomic Masses andIsotopic Abundances

natural atomic masses =

SUM[(atomic mass of isotope)

*(fractional isotopic abundance)]

Dr. S. M. Condren

Example: Chlorine has two isotopes, Cl-35 and Cl-37, which have masses of 34.96885 and 36.96590 amu, respectively. The natural atomic mass of chlorine is 35.453 amu. What are the percent abundances of the two isotopes?

let x = fraction Cl-35 y = fraction Cl-37

x + y = 1 y = 1 - x

(AW Cl-35)(fraction Cl-35) + (AW Cl-37)(fraction Cl-37) = 35.453

Thus: 34.96885*x + 36.96590*y = 35.453

34.96885*x + 36.96590*(1-x) = 35.453

x = 0.75757 <=> 75.757% Cl-35 Thus 24.243% Cl-37

Dr. S. M. Condren

Molar Mass-Molecular Weight

Sum

atomic masses

represented by formula

atomic masses => gaw

molar mass => MM

Dr. S. M. Condren

Example

What is the molar mass of ethanol, C2H5O1H1?

MM = 2(gaw)C + (5 + 1)(gaw)H + 1(gaw)O

= 2(12.011)C + 6(1.00794)H + 1(15.9994)O

= 24.022 + 6.04764 + 15.9994

= 46.069 g/molSignificant figures rule for multiplication

Significant figures rule for addition

Sequence – multiplication then addition,apply significant figure rules in proper sequence

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The Mole

• a unit of measurement, quantity of matter present

• Avogadro’s Number6.022 x 1023 particles

• Latin for “pile”

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One Mole of each Substance

Clockwise from top left:1-Octanol, C8H17OH;Mercury(II) iodide, HgI2;Methanol, CH3OH; andSulfur, S8.

Dr. S. M. Condren

ExampleHow many moles of carbon dioxide

molecules are there in 10.00g of carbon dioxide?

MM = 1(gaw)C + 2(gaw)O = 44.01 g/mol

#mol CO2 = (10.00g)(1 mol/44.01g)/ /= 0.2272 mol

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Missing elements: 44, 68, 72, & 100 amu

Mendeleev’s Periodic Table

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Properties of Ekasilicon

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Modern Periodic Table

the elements are arranged according to increasing atomic numbers

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I A II A III B IV B V B VI B VII B VIII B I B II B III A IV A V A VI A VII A VIII A1 1 2

1 H H He1.008 1.008 4.0026

3 4 5 6 7 8 9 10

2 Li Be B C N O F Ne6.939 9.0122 10.811 12.011 14.007 15.999 18.998 20.183

11 12 13 14 15 16 17 18

3 Na Mg Al Si P S Cl Ar22.99 24.312 26.982 28.086 30.974 32.064 35.453 39.948

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr39.102 40.08 44.956 47.89 50.942 51.996 54.938 55.847 58.932 58.71 63.54 65.37 69.72 72.59 74.922 78.96 79.909 83.8

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe85.468 87.62 88.906 91.224 92.906 95.94 * 98 101.07 102.91 106.42 107.9 112.41 114.82 118.71 121.75 127.61 126.9 131.29

55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

6 Cs Ba **La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn132.91 137.33 138.91 178.49 180.95 183.85 186.21 190.2 192.22 195.08 196.97 200.29 204.38 207.2 208.98 * 209 * 210 * 222

87 88 89 104 105 106 107 108 109 110 111 112 113 114 115 116 118

7 Fr Ra ***Ac Rf Ha Sg Ns Hs Mt Uun Uuu Uub Uut Uuq Uup Uuh Uuo* 223 226.03 227.03 * 261 * 262 * 263 * 262 * 265 * 268 * 269 * 272 * 277 *284 *285 *288 *292 *294

Based on symbols used by ACS S.M.Condren 2006

58 59 60 61 62 63 64 65 66 67 68 69 70 71

* Designates that **Lanthanum Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Luall isotopes are Series 140.12 140.91 144.24 * 145 150.36 151.96 157.25 158.93 162.51 164.93 167.26 168.93 173.04 174.97

radioactive 90 91 92 93 94 95 96 97 98 99 100 101 102 103

*** Actinium Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Series 232.04 231.04 238.03 237.05 * 244 * 243 * 247 * 247 * 251 * 252 * 257 * 258 * 259 * 260

Periodic Table of theElements

Periodic Table of the Elements

Dr. S. M. Condren

Organization of Periodic Table• period - horizontal row• group - vertical columnFamily Names• Group IA alkali metals• Group IIA alkaline earth metals• Group VIIA halogens• Group VIIIA noble gases• transition metals• inner transition metals

– lanthanum series rare earths– actinium series trans-uranium series

Dr. S. M. Condren

Dr. S. M. Condren

ELEMENTS THAT EXIST AS MOLECULES

ELEMENTS THAT EXIST AS MOLECULES

Allotropes of CAllotropes of CAllotropes of CAllotropes of C

Dr. S. M. Condren

Dr. S. M. Condren

ELEMENTS THAT EXISTAS DIATOMIC MOLECULES

Dr. S. M. Condren

White P4 and polymeric red phosphorus

S8 sulfur molecules

ELEMENTS THAT EXISTAS POLYATOMIC MOLECULES