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

Chapter 2

Elements & Atoms

Atomic Structure

Electrical charges of the same type repel one another, and charges of the opposite type attract one another.

Radioactivity

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

Millikan’s Experiment

Rutherford’s Experiment

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

• charged single atom

• charged cluster of atoms

Ions

• cations– positive ions

• anions– negative ions

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

Metric Prefixes

Relative size of atom

and atomic nucleus

Scanning Tunneling Microscope

Measurement and Units

length - meter

volume - liter

mass - gram

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

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

• 1 proton and 1 neutron in nucleus

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

• 1 proton and 2 neutrons in nucleus

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

Nuclear Notation

X-A

• C-12

XA

• C12

ZXA

• 6C12

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

Mass Spectrometer

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”

Molar Mass

Sum

atomic masses

represented by formula

atomic masses gaw

molar mass MM

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.

Modern Periodic Table

the elements are arranged according to increasing atomic numbers

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

Organization of Periodic Table

• period – horizontal row

• group – vertical column

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

Types of Elements

metals

nonmetals

metalloids – semimetals