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CHEMISTRYThe Molecular Science
Chapter two
Slides prepared by
S. Michael Condren
Department of Chemistry
Christian Brothers University
to Accompany
CHEMISTRY The Molecular Scienceby John W. Moore, Conrad Stanitski, & Peter C. Jurs
Atomic Structure
Electrical charges of the same type repel one another, and charges of the opposite type attract one another.
Alpha Radiation
• composed of 2 protons and 2 neutrons
• thus, helium-4 nucleus
• +2 charge
• mass of 4 amu
• creates element with atomic number 2 lower
Beta Radiation
• composed of a high energy electron which was ejected from the nucleus
• “neutron” converted to “proton”
• very little mass
• -1 charge
• creates element with atomic number 1 higher
Gamma Radiation
• nucleus has energy levels
• energy released from nucleus as the nucleus changes from higher to lower energy levels
• no mass
• no charge
Structure of the Atom
• electrons– found in electron cloud
– relative charge of -1
– relative mass of 0.00055 amu
• protons– found in nucleus
– relative charge of +1
– relative mass of 1.0073 amu
• neutrons– found in nucleus
– neutral charge
– relative mass of 1.0087 amu
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
Ions
• cations– positive ions
• anions– negative ions
• ionic compounds– combination of cations and anions– zero net charge
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
Isotopes
• atoms of the same element which differ in the number of neutrons in the nucleus
• designated by mass number
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
Mass Number, A
• integer representing the approximate mass of an atom
• equal to the sum of the number of protons and neutrons in the nucleus
Masses of Atoms
Carbon-12 Scale
Masses of the atoms are compared to the mass of C-12 isotope having a mass of 12.0000
Atomic Masses andIsotopic Abundances
natural atomic masses =
sum[(atomic mass of isotope)
(fractional isotopic abundance)]
The Mole
• a unit of measurement, quantity of matter present
• Avogadro’s Number6.022 1023 particles
• Latin for “pile”
Example
How many grams of Cu are there in 5.67 mol Cu?
#g Cu = (5.67 mol)(63.546g/mol)
= 360. gAtomic mass of Cu
Example
Calculate the number of boron atoms in 1.000g sample of the element.
#B atoms = (1.000g)(1mol / 10.81g)
(6.022 1023atoms/mol)
= 5.571 1022 B atoms
Example
How many moles of silicon, S, are in 30.5g of S?
#mol Si = (30.5g)(1 mol/32.06g)
= 0.951 mol Si
Example
What is the molar mass of methanol, CH3OH?
MM = 1(gaw)C + (3 + 1)(gaw)H + 1(gaw)O
= 1(12.011)C + 4(1.00794)H + 1(15.9994)O
= 22.042 g/mol
Example
How many moles of carbon dioxide molecules are there in 6.45g of carbon dioxide?
MM = 1(gaw)C + 2(gaw)O = 44.01 g/mol
#mol CO2 = (6.45g)(1 mol/44.01g)
= 0. 147 mol
Development of Periodic Table
Newlands - English
1864 – Law of Octaves – every 8th element has similar
properties
Development of Periodic Table
Mendeleev
• Russian
• 1869 - Periodic Law
• allowed him to predict properties of unknown elements
Mendeleev’s Periodic Table
the elements are arranged according to increasing atomic weights
Missing elements: 44, 68, 72, & 100 amu
Predicted Properties of Ekasilicon
Property Ekasilicon Germanium
Atomic Weight 72 72.6
Color gray gray
Density, g/mL 5.5 5.36
Oxide EsO2 GeO2
Chloride EsCl4 GeCl4
Modern Periodic TableMoseley, Henry Gwyn Jeffreys
1887–1915, English physicist.
• studied the relations among spectra of different elements.
• concluded that the atomic number is equal to the charge on the nucleus based on the x-ray spectra emitted by the element.
• explained discrepancies in Mendeleev’s Periodic Law.
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 89 104 105 106 107 108 109 110 111 112 114 116 118
7 Fr Ra ***Ac Rf Ha Sg Ns Hs Mt Uun Uuu Unb Uuq Uuh Uuo* 223 226.03 227.03 * 261 * 262 * 263 * 262 * 265 * 268 * 269 * 272 * 277 *285 *289 *293
Based on symbols used by ACS S.M.Condren 2001
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 the ElementsPeriodic Table of the Elements
Family Names
Group IA alkali metals
Group IIA alkaline earth metals
Group VIIA halogens
Group VIIIAnoble gases
transition metals
inner transition metals
• lanthanum series rare earths
• actinium series trans-uranium series