Lecture 4. Chapter 2. Structure of the Atom Contd.

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Lecture 4. Chapter 2. Structure of the Atom
(Contd.)
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Lecture 4.

• Exercise 2.1. A US penny is 19 mm across. How
  many Ag atoms could span this if diameter Ag atom
  is 2.88 Å? Note 1 Ag atom per 2.88 Å.
• Conversion factors 1 10-3 m/1 mm and
• 1 10-10 m/ 1 Å.
• Number 19 mm x 10-3 m x 1 Ag atom x 1 Å
• 1 mm 2.88 Å
  10-10 m
• 6.6 x 107 Ag atoms
• which is sixty six million Ag atoms.

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Diameters of Atomic Nuclei.

• These are on the order of 10-4 Å. So if we
  draw an atom on the board with a diameter of 1m,
  then the nucleus will be 0.1 mm across!

diameter of nucleus 0.1 mm
Diameter 1 meter
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Atomic numbers, mass numbers, and Isotopes. (p.
45).

• The chemical properties of the elements are
  controlled by the numbers of electrons and
  protons. The number of protons ( no. of
  electrons) is the Atomic Number (Z) of the
  element.

Z 1 6 8
13
protons
H C
O Al
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Mass Number

• The Mass Number is the sum of the number of
  protons plus neutrons. Atoms of a given element
  can have different numbers of neutrons. Thus, C
  (carbon) always has Z 6, i.e. it has 6 protons,
  since C determines its chemistry, but can have
  different numbers of neutrons.

Nuclei of Carbon atoms
all have six protons (red)
six neutrons (blue)
eight neutrons
carbon-12 carbon-13 carbon-14
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Isotopes

• Different isotopes of the same element have
  different mass numbers. Thus, 12C and 14C both
  have 6 protons (Atomic Number 6), but 12C has 6
  neutrons, while 14C has 8.

C
Mass number 14 Atomic number 6
carbon-14
Usually, only the mass number is indicated,
and referred to as carbon-14.
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Isotopes of Hydrogen (Z 1)
one proton one proton,
one proton in nucleus one
neutron two neutrons
Hydrogen Deuterium
Tritium 99.9844 0.0156
radioactive, unstable
1 2
3
H H
H
1 1
1
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The 12C atom
nucleus contains 6 protons (Z 6) and 6
neutrons
6 electrons
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2.4. Atomic weights.

• These are expressed in amu. The mass of the
  12C isotope has been defined as exactly 12 amu. 1
  amu 1.66054 x 10-24 g, or 1/6.022 x 1023 g. In
  these units, the 1H isotope has a mass of 1.0078
  amu.

The mass of the 12C isotope is exactly 12 amu.
Carbon-12
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Atomic weights of the elements

• Elements usually consist of mixtures of
  isotopes. The Atomic Weights for the elements are
  thus the average masses of these mixtures,
  expressed in amu. Thus, naturally occurring C
  consists of 98.93 12C and 1.07 13C. The Atomic
  Weight of the mixture is thus given by
• Atomic weight 98.93 x 12 1.07 x 13.0335
• 100 100
• 12.01 amu.

Divide by 100 because per one hundred
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Average Atomic Mass Atomic Weight
EXAMPLE Si naturally occurs in three
isotopes 92.2 of 28Si (27.98 amu) 4.7 of 29Si
(28.98 amu) 3.1 of 30Si (29.97 amu) what is the
atomic weight of Si?
92.2 100
0.922 x 27.98 amu 0.047 x 28.98 amu 0.031 x
29.97 amu 28.09 amu
add together
4.7 100
3.1 100
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2.5. The Periodic Table.

• The Periodic Table is the most important tool
  that chemists use for organizing and remembering
  chemical facts. The chemical properties show a
  periodic pattern, hence periodic table.
  Mendeleev in 1869 came up with the arrangement we
  now essentially use, possibly from the
  arrangement of cards in solitaire.

Dmitri Ivanovich Mendeleev
(1834-1907)
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Solitaire
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(No Transcript)
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Periodic Table
Elements are sorted according to increasing
atomic number
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C
12.01
Atomic weight
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Groups in the periodic table
Group 7
Group 5
Group 1
Group 3
Group 1B
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Groups

• The vertical columns in the periodic table are
  called GROUPS. Properties repeat down a group,
  such as Alkali metals (Group 1) are all soft
  silvery reactive metals that form basic
  hydroxides, while Noble gases (group 8) are all
  chemically unreactive gases, halogens (group 7)
  all exist as X2 molecules, and form salts where
  they are the anion X-.

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Group 1B, the coinage metals
Cu Ag
Au
Copper penny American silver South
African
Eagle Gold Krugerrand
They are all relatively inert, corrosion-resistant
metals which have been used for minting coins.
They are all excellent conductors of
electricity. They all can form chlorides of
the composition MCl (M metal), such as CuCl,
AgCl, and AuCl.
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Numbers Down side Indicate period
Rows or Periods in the Periodic Table (these run
across the periodic table)
First period contains only H and He
third period
5th period
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HW 37
Periodic Table
Most elements are metals
VIII A
I A
II A
III A
IV A
VA
VI A
VIIA
Non- metals
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Molecules and Molecular Compounds
Some elements exist as diatomic molecules
at room temp. H2 N2
O2 F2 Cl2 Br2 I2
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Periodic table helps predict formulas of
compounds
e.g. fluorides of metallic elements Group 1 HF,
LiF, NaF, KF, RbF, CsF
Group 3A. BF3, AlF3, GaF3, InF3
Group 2. BeF2, MgF2, CaF2, SrF2, BaF2
Group 3B. ScF3, YF3, LaF3, AcF3.
Group 2B. ZnF2, CdF2, HgF2
Metallic elements
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Periodic table helps predict formulas of
compounds

• e.g. Hydrides (compounds with hydrogen) of
• non-metallic elements

Group 7. HF, HCl, HBr, HI.
Group 6. H2O, H2S, H2Se, H2Te
inert
Group 5. NH3, PH3, AsH3, SbH3
Group 4. CH4, SiH4, GeH4
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Atoms of the first four elements in the periodic
table
1 4 7
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1H 2He 3Li 4Be
Hydrogen Helium Lithium
Beryllium
protons 1 2
3 4 Neutrons 0
2 4
5 Electrons 1 2
3 4
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Atoms and ions

• An atom can lose one or more electrons to
  become a positively charged cation, or gain
  electrons to become a negatively charged anion

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This has an effect when we count electrons in
elements and Ions
one extra compared to Z
neutral atom, same as Z
two less compared to Z
number of protons (Z)
number of electrons
number of neutrons
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32S
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32 16 16
35 1 36
80 35 45
80Br-
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20
40Ca2
20 - 2 18
40 20 20
- charge results in gain of one electron
2 charge results in loss of two electrons
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Molecules and Molecular Compounds
The periodic table helps predict how elements
combine
Empirical Formulas
Molecular Formulas
Only gives relative number of atoms in compound
Show actual number and types of atoms in a
molecule
Subscripts are smallest whole-number ratios
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Empirical Formulas
Molecular Formulas
H2O2
HO
Hydrogen peroxide
C4H10
C2H5
Butane
C3H8
C3H8
Propane
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Empirical and molecular formulae of glucose
hydrogen (white)
oxygen (red)
Empirical Formula CH2O Molecular Formula C
6H12O6 ( empirical formula x 6)
carbon (cyan)
If you count the atoms in this model of glucose
you will see 6 carbons, 12 hydrogens, and
6 oxygens
glucose
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Different representations of methane (CH4)
Structural formula

• Space-filling model

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Ions and Ionic Compounds
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Which Elements form Anions, which Cations?
Metals tend to form Cations
Nonmetals tend to form Anions
VIII A
I A
II A
III A
IV A
VA
VI A
VIIA
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Cations and Anions can combine to form Ionic
Compounds
Sodium cation, Na
Chloride anion, Cl-
Sodium chloride crystal
Sodium chloride
(Ionic Crystal not a discrete molecule)
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Empirical Formulas for Ionic Compounds
(A) determine charge on ions formed
(B) add ions so that compound is neutral overall
Na, O
Al, O
Na
O2-
O2-
Al3
Al3
2 Na
O2-
O2-
Na2O
Al2O3
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A simple approach simply swap the charge on one
ion to be the subscript on the other
charges
2-
3
Al2O3
Al
O
subscripts
MgCl2
Ca2O2
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2.8 Naming Inorganic Compounds.

• There are now more than 19 million known chemical
  substances. We cannot use common names for all of
  them, e.g. rock salt or sugar. We need a
  system of naming them that indicates
  unambiguously what they are.

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Organic and Inorganic substances

• Organic substances are compounds of carbon and
  hydrogen (plus other elements such as N or S)
  associated with living things. Inorganic
  substances are substances not associated mainly
  with living things.

CH2CH2OH
AlCl3 Ethanol aluminum
chloride Organic
Inorganic
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Naming Ionic Compounds

• These consist of metal cations (e.g. Na)
  combined with non-metal anions (e.g. Cl-).
• 1. Positive cations
• a) Cations formed from the metal are given the
  same name as the metal e.g. Sodium, Aluminum,
  Zinc.

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• b). If a metal can form cations of different
  charge, this is indicated with Roman numerals,
  e.g.
• Fe2 iron (II) Fe3 iron(III)
• Cu copper(I) Cu2 copper(II).
• An older method still widely used uses Latin
  names where the suffix OUS indicates the lower
  charge, and IC indicates the higher charge
• Fe(II) ferrous Fe(III) ferric
• Cu(I) cuprous Cu(II) cupric

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2. Negative ions (Anions).

• a) The names of monoatomic anions are formed
  by replacing the ending of the name of the
  element with ide.
• H- hydride ion Cl- chloride O2-
  oxide N3- nitride S2- sulfide
• A few simple polyatomic anions also get the
  suffix ide
• OH- hydroxide CN- cyanide O22- peroxide

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Oxo-anions (sulfate, sulfite, nitrate, nitrite)

• b) Polyatomic anions containing oxygen end in
  ATE (more oxygens) or ITE (fewer oxygens).
• more oxygens
• NO3- nitrate SO42- sulfate
• NO2- nitrite SO32- sulfite
• fewer oxygens

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The oxo-anions of chlorine

• Prefixes are used when there are more than two
  different oxo-anions of the same element
• Cl- chloride
• ClO- hypochlorite
• fewer oxygens ite
• ClO2- chlorite
• ClO3- chlorate
• more oxygens ate
• ClO4- perchlorate

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Carbonate and hydrogen carbonate

• c) Anions derived from other anions by addition
  of hydrogen
• CO32- carbonate ( H) ?
• HCO3- hydrogencarbonate

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3. Ionic compounds.

• These are named with the cation name first,
  followed by the name of the anion
• NaCl sodium chloride
• Na2CO3 sodium carbonate
• Al(NO3)3 aluminum nitrate
• Cu(ClO4)2 copper(II) perchlorate or
• cupric perchlorate

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Names and Formulas of Binary Molecular Compounds.

• Binary compounds are two-element compounds,
  e.g. carbon dioxide. Rules for naming these are
  as follows
• 1. The name of the element further to the left in
  the periodic table is usually written first. Thus
  oxygen is always written last except when
  combined with fluorine. OF2 oxygen difluoride,
  but Cl2O is dichlorine monoxide.
• 2. If elements are in same group, heavier element
  is written first, e.g. SO2 sulfur dioxide.
• 3. the name of the second element is given an
  IDE ending.

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Numerical prefixes

• 4. Greek prefixes are used to indicate the number
  of atoms of each element in the formula
• SF6 sulfur hexafluoride
• NF3 nitrogen trifluoride
• N2O4 dinitrogen tetroxide.
• P4S10 tetraphosphorus decasulfide.
• (A table of Greek prefixes is given on next slide)

Note here the a in tetra is omitted
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Table of Greek prefixes (bottom left p. 66)

• mono- 1
• di- 2
• tri- 3
• tetra- 4
• penta- 5
• hexa- 6
• hepta- 7
• octa- 8
• nona- 9
• deca- 10
• Note that if the name of the second element
  starts with a vowel, e.g. oxide, then the -a is
  omitted for
• tetra-, penta-, and hepta-, so we have
  disulfur tetroxide, phosphorus pentoxide,
  diiodine heptoxide.