Introductory Chemistry B CH4751 Dr' Erzeng Xue

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Introductory Chemistry B CH4751Dr. Erzeng Xue
CH4751 Lecture Notes 1 (Erzeng Xue)
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Course General Information
CH4751 Lecture Notes 1 (Erzeng Xue)

• Lectures Room C1061
• Time Monday 5pm, Tuesday 2pm
• Notes Available at the class and on the ULs
  web
• Labs Room B3-053,
• Time Friday 4pm, Weeks 3, 5, 7, 9, 11
• Attendance is MANDATORY
• MUST have white lab coat and safety specs
• Assessment 75 End term Exam
• 25 Lab. Attendance/Reports

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CH4751 Course Syllabus
CH4751 Lecture Notes 1 (Erzeng Xue)
Course General Information

• Fundamental Laws, Dimensions and Units of
  Measurement
• Matter, Composition, Structure and Properties
• Classification and Composition
• Atoms, Molecules Ions
• Chemical Bonding
• Periodic Nature of elements
• The mole definition and use
• Change in Composition and Structure - Chemical
  Reactions
• Reaction Process and Types of Reaction
• Reaction Stoichiometry
• Direction of a Reaction and Energy Change
  Associated with it
• The Extent of Reaction and Chemical Equilibrium
• Rate of Reaction and Concept of Catalysis
• Chemistry of Selected Systems
• Chemical Reactions Involving Multi Phases
• Acid, base and pH
• Quantum Chemistry Its Applications in Chemical
  Modelling Spectroscopes
• Chemistry in Specialised Areas
• Introduction to Organic Chemistry / BioChemistry
  (depending on the availability of time)

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Recommended Texts
CH4751 Lecture Notes 1 (Erzeng Xue)
Course General Information

• Available in UL Bookshop as follows
• Brown, LeMay Bursten, Chemistry The Central
  Science, 9th ed.
• Zumdahl, Chemistry 5th ed.
• Atkins Jones, Chemistry Molecules, Matter,
  and Change, 3rd edn.
• Available in UL library
• General Chemistry texts Classification Number
  540

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Experiments
CH4751 Lecture Notes 1 (Erzeng Xue)

• There are 5 experiments
• Separation of sand and salt
• Assay of an industrial Etchant solution by
  acid-base titration
• A series of reactions involving compounds of
  copper
• The oxidising capacities of household bleaches
• Indicators and acid-base dissociation constants

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What Is Chemistry ?
CH4751 Lecture Notes 1 (Erzeng Xue)

• Describes
• Structure composition of matter (at both macro
  and micro levels)
• Changes in structure composition
• Energy involved in these changes

Why Study Chemistry ?

• Understand our world and how it works
• Chemistry is the central science
• Educate
• This module is the foundation course on which you
  can further build up your knowledge of chemistry
  in other areas

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How To Study Chemistry ?
CH4751 Lecture Notes 1 (Erzeng Xue)

• Fundamental laws
• Using clear language
• Clear definition of terms used
• logic description of known facts
• Using scientific methods
• Observation of true fact
• Carefully designed experiments
• Modelling
• Classification of known information

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Where Are You Standing Now?
CH4751 Lecture Notes 1 (Erzeng Xue)
Targeted Your Chemistry Knowledge After CH4751
Your Leaving Cert Chemistry Knowledge
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Fundamental laws
CH4751 Lecture Notes 2 (Erzeng Xue)

• Law of Conservation of Energy
• Energy can be neither created nor destroyed, but
  may be transformed from one form to another
• Law of Conservation of Mass
• Mass cannot be created or destroyed. The total
  mass of substances involved in a physical or
  chemical change remains constant

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Dimensions and Units
CH4751 Lecture Notes 2 (Erzeng Xue)

• DIMENSON
• Many things happening in a process (naturally or
  in an experiments)
• What are these things or quantities?
• How many quantities are involved?
• Are these quantities dependent or independent?
• UNIT
• What is the scale of a quantity (big or small)?
• To describe a quantity quantitatively
• To compare the same quantity
• at different stage of a process, or
• in two different processes
• Dimension and unit provide the base of
  scientific language

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Fundamental Dimensions
CH4751 Lecture Notes 2 (Erzeng Xue)
Dimensions and Units

• There are 7 independent dimensions

Note There are several unit systems in use. The
most commonly used ones are S.I. (preferred) and
English.
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Use of Dimensions and Units
CH4751 Lecture Notes 2 (Erzeng Xue)
Dimensions and Units

• All other quantities can be expressed in terms of
  these fundamental quantities
• For complex situation derived units may be used
• e.g. velocity would have dimension LT-1
• For each dimension unit can be in different scale
  
• e.g. velocity would have unit m/s, km/hr etc.
• An unit for the same dimension in different
  systems can be converted
• e.g. velocity 120 miles/hr 195.6 km/hr 3260
  m/min
• A quantitative description consists of 2 parts
• number unit e.g. velocity 10 m/s,
• the number used is depending on the unit used.
• Different dimensions cannot be added, subtracted
  or equated

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Derived Units
CH4751 Lecture Notes 2 (Erzeng Xue)
Dimensions and Units

• A combination of different quantities
  representing a physical measurement can be
  expressed by using a Derived Unit
• Quantity Definition Derived Unit
• Area Length x length m2
• Volume Area x length m3
• Density Mass / unit volume kg m-3
• Speed Distance / unit time m s-1
• Acceleration Change in speed / unit time m
  s-2
• Force Mass x acceleration kg m s-2 (Newton, N)
• Pressure Force / unit area kg m-1 s-2 (Pascal,
  Pa)
• Energy Force x distance kg m2 s-2 (Joule, J)

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Unit Conversion
CH4751 Lecture Notes 2 (Erzeng Xue)
Dimensions and Units

• Procedure of unit conversions
• a) Find equivalent of the unit
• e.g. 1 inch 2.54 cm (Equivalence Statement)
• b) Write the unit factors
• e.g. (2.54 cm/1in) and (1 in/2.54 cm)
• c) Use proper unit factor in your calculation
• e.g. A pencil is 7 inches long. Whats its
  length in cm?
• 7 in x (2.54 cm/1in) 17.8 cm
• Exercises
• 1. A gas is at pressure of 29.7 psi, what is the
  pressure in atm? Write the conversion process.
• 2. When 1 litre of water at 20 C is heated to
  100C, what is the volume of water vapour formed
  at 1 atm at 100C?
• 3. A temperature of 104 Fehrenheit was read.
  What is this temperature in Celsium scale?

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Important Notes
CH4751 Lecture Notes 2 (Erzeng Xue)
Dimensions and Units

• When quoting any quantity always quote both the
  number and unit
• A number without unit has no definite meaning in
  physics and chemistry
• When performing calculation always use the same
  unit system
• If the date collected contain the quantities in
  different unit system, make conversion so that
  all the quantities are described in the same
  system before further calculation
• Check the unit of a quantity before performing a
  calculation
• Only the numbers with the same unit can be added,
  subtracted and equated

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Uncertainty in Measurement
CH4751 Lecture Notes 2 (Erzeng Xue)
Dimensions and Units

• Uncertainties always exist in measured quantities
• Caused by equipment errors, human errors
• Accuracy
• measure of how close measurement is to its real
  (or true) value
• Precision
• measure of how close successive measurements are
  to each other
• Precise measurements can be inaccurate

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Matter and Its Classification
CH4751 Lecture Notes 3 (Erzeng Xue)
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Physical State and Examples
CH4751 Lecture Notes 3 (Erzeng Xue)
Matter its classification

• Solid
• rigid, fixed volume and shape
• Liquid
• definite volume but no distinct shape
• Gas (vapour)
• no fixed volume or shape conforms to that of its
  container
• Compressibility
• Change in volume under pressure
• Solids and liquids are only slightly compressible
• Gases are highly compressible

Plutonium
Mercury
Chlorine
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Chemical Composition and Examples
CH4751 Lecture Notes 3 (Erzeng Xue)
Matter
Matter its classification

• Pure substance
• It has a definite chemical composition and
  properties.
• It cannot be separated into simpler substances
  by physical means.
• Element
• pure substance which cannot be further broken
  down by ordinary chemical means.
• Compound
• pure substance which is composed of 2 or more
  elements and can be further broken down by
  chemical means.
• Mixture
• contains 2 or more pure substances, which can be
  separated out by physical means.
• can be homogeneous (uniform throughout, e.g. air)
  and heterogeneous (not uniform throughout, e.g.
  wood)

carbon
ice
bronze
agate
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Comparison Mixtures vs. Compounds
CH4751 Lecture Notes 3 (Erzeng Xue)
Matter its classification

• Differences between a mixture and a compound

• Examples
• Which of the materials below are pure substances
  and which are mixtures? What is physical states
  of each under normal conditions?
• water, salt, paper, milk, apple, vegetable oil,
  petrol, cotton, vitamin tablets, natural gas,
  soil, beer, wine.

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Matter and Its Properties
CH4751 Lecture Notes 3 (Erzeng Xue)
Matter
Physical properties
Chemical properties
Some examples are reactivity, corrosive
nature acidity/basicity, toxicity etc.
Some examples are state (solid, liquid,
gas) melting/boiling point, thermoconductivity,
density, etc

• Q1. Where can one get physical /chemical
  properties of a substance?
• physical chemistry handbooks.
• Q2. Why are physical/chemical properties
  different?
• The composition structure
• Q3. Are there theories to explain/help us to
  understand the different properties of various
  substances?
• Yes. The structure of atoms of constituent
  elements and how these atoms are stuck on each
  other in a molecule (chemical bonding).

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Atoms and Molecules
CH4751 Lecture Notes 3 (Erzeng Xue)

• Atom
• Smallest particle of an element which can
  undergo chemical changes in a reaction
• Note Atom - we mean each individual particle
  of an element (microscopic)
• Element - we mean the collective of atoms of
  the same kind (macroscopic)
• Molecule
• Smallest particle of a compound which can exist
  and still retain the chemical properties of the
  compound.
• Note Molecule can be a single atom or several
  atoms binding each other in a specific way
• Molecule - we mean each individual particle
  of a compound (micro-)
• Compound - we mean the collective of molecules
  of the same kind (macro-)

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Structure of the Atoms
CH4751 Lecture Notes 3 (Erzeng Xue)
Atoms Molecules
Electron clouds
5x10-15 m
Nucleus - consists of protons and neutrons
Some basic fact about the atom Size 0.1 to 0.5
nanometers (1 nm 1x10-9 m) Composition
contains electrons (e), protons (p), and
neutrons (n), with the exception of
hydrogen. Mass H atom 1.67x10-24g
1.008 atomic mass units (a.m.u.) C atom
2x10-23g 12.000 a.m.u. Electrical charge
neutral particle mass (a.m.u.) charge
e- 0.0005 - 1 p 1.007
1 n 1.009 0
0.1- 0.5 x 10-10 m
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Structure of the Atoms
CH4751 Lecture Notes 3 (Erzeng Xue)
Atoms Molecules

• Important points
• The number of electrons protons in an atom are
  equal - zero net electrical charge
• The nucleus of an atom is very small in
  comparison with the overall size of an atom
• Density of the nucleus of an atom is huge (of the
  order of 1013-1014 g/cm3) because
• the nucleus carries most of the atoms mass
  (protons neutrons) in its tiny volume
• Electrons take up most of the volume of the atom
  and play the key role in chemical reactions
• Comparison of Atom Size with everyday objects
• Q1. The diameter of a carbon atom is 1.5 x 10-10
  m. How many carbon atoms could be aligned side
  by side in a straight line across the width of a
  pencil line that is 0.2mm wide?
• A. 0.2 x 10-3m/ 1.5 x 10-10m 1.3 x 106 C atoms
• Q2. The diameter of a 2 cent coin is 19 mm while
  the diameter of a silver atom is 2.88x10-10 m.
  How many silver atoms could be arranged side by
  side in a straight line across the diameter of
  it?
• A. 19 x 10-3m/ 2.88 x 10-10m 6.6 x 107 Ag
  atoms

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Atoms and Elements
CH4751 Lecture Notes 4 (Erzeng Xue)
Atoms Molecules

• Atom
• Atom - individual particle.
• - We say a hydrogen atom, a chlorine atom
• Element
• Collective of atoms of the same kind.
• Each element is given a specific symbol. Usually
  the symbol is taken from the 1st one or two
  letters, with some exception such as iron-Fe,
  gold-Au, silver-Ag, etc.
• Some of the more common elements
• Element Symbol Element Symbol
• Hydrogen H Helium He
• Carbon C Aluminium Al
• Nitrogen N Oxygen O
• Phosphorous P Iron Fe
• Copper Cu Nickel Ni
• Sulphur S Iodine I

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Molecules and Compounds
CH4751 Lecture Notes 4 (Erzeng Xue)
Atoms Molecules

• Molecule
• It can be a single atom or several atoms stuck
  on (chemical bond) each other in a specific way.
  
• E.g. We say carbon molecule, C, chlorine
  molecule, Cl2, water molecule, H2O.
• The properties of a molecule are related to the
  constituent atoms but also depending on how these
  atoms are bonded together
• Atoms are the basic building blocks for molecules
• Compound
• Collective of molecules of the same kind.
• We say hydrogen (compound), H2, chlorine
  (compound), Cl2, water, H2O etc.
• Q. What we call CO, an atom? an element? a
  molecule? a compound?

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Elements
CH4751 Lecture Notes 4 (Erzeng Xue)
Atoms Molecules

• A How many elements are there?
• So far we have identified around 120 (some of
  them exist only a short time in lab
• (Note we dont say how many atoms we found. it
  depends on the quantity of an element)
• How many compounds are there?
• Many, many. There are more new compounds found
  and invented
• (Note We dont say how many molecules we found.
  its number depends on the quantity of a compound)

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Periodic Table of Elements
CH4751 Lecture Notes 4 (Erzeng Xue)
Atoms Molecules

• Different element refers different matter - are
  there any relation/trend?
• Yes. they can be arranged according to their
  atomic mass electronic structure
• Periodic table of elements showing the atomic
  number

Symbol of element
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Cl
35.45
atomic number
atomic mass
Note - The symbols used for elements are
universally adapted. - There are different
notation systems in use. Check the keys.
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Isotopes and Atomic Mass
CH4751 Lecture Notes 4 (Erzeng Xue)
Atoms Molecules

• Isotopes
• Atoms of the same element having different no. of
  neutrons, thus different masses
• e.g. hydrogen deuterium tritium
• molecules consist of atoms having different no.
  of eutrons are also called isotopes.
• Atomic mass
• is the average of the isotope masses of an
  element, weighted to reflect their relative
  natural abundances
• Example Chlorine has two naturally occurring
  isotopes, 35Cl (A34.97a.m.u.) and 37Cl (A
  36.96 a.m.u.). The respective natural abundances
  of these isotopes are 75.5 and 24.5.
• (average) atomic mass
• Note atomic mass is also called as atomic
  weight

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Atoms, Molecules and Ions
CH4751 Lecture Notes 4 (Erzeng Xue)
Atoms Molecules

• Ions
• In some situations (in a chemical reaction or an
  acid/base dissolved in water), atoms or molecules
  have gained or lost one or more electrons.
• e.g. H OH- SO4 (or SO4-2)
• Ions can carry positive charge when lost
  electrons, e.g. H
• Ions can carry negative charge when gained
  electrons, e.g. OH-, SO4
• Note the superscript refers to the number of
  electrons gained or lost.

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Inter-Conversion Chart
CH4751 Lecture Notes 4 (Erzeng Xue)
Atoms Molecules
Elements
Compounds
Identical
atoms
Atoms
Molecules
e-
n
e-
n
Ions
Isotopes
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Molecule Mass
CH4751 Lecture Notes 4 (Erzeng Xue)
Atoms Molecules

• Molecular mass is the sum of the atomic masses of
  all of the constituent atoms in a molecule.
• Example 1 Molecular mass (M.M.) of H2?
• Atomic Mass (A.M.) of H 1.008 a.m.u.
• M.M. of H2 2 x 1.008 2.016 a.m.u.
• Example 2 M.M. of carbon monoxide, CO?
• A.M. of C 12.0 a.m.u., A.M. of O 16.0 a.m.u
• M.M. of CO 1x12.0 1x16.0 28.0 a.m.u.
• Example 3 M.M. of glucose, C6H12O6?
• A.M. of C12.0 a.m.u., A.M. of H is 1.0 a.m.u.,
  A.M. of O16.0 a.m.u
• M.M. of C6H12O6 6x(12.0 a.m.u.) 12x(1.0
  a.m.u.) 6x(16.0 a.m.u)
• 180.0 a.m.u.
• Note molecule weight (unit g/mol) equals to
  molecule mass in value but refers to a different
  unit.

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Chemical Bondings
CH4751 Lecture Notes 5 (Erzeng Xue)

• A chemical bonding
• refers to a specific way atoms are held together
  in a molecule by certain forces
• A chemical reaction always involves bond
  reconstruction (in most cases bond-breaking and
  reformation)
• The properties of a resultant molecule depend not
  only on those of constituent atoms but also how
  they are bonded together
• An atom may form one type of bond with certain
  atoms and another type bond with other type of
  atoms, depending on the nature of the bonding
  atoms
• Types of chemical bonds
• Ionic
• Covalent
• Dative (or coordinate) covalent
• Atomic structure, especially the orbital theory,
  is the basis of chemical bonding

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Classical Orbital Theory
CH4751 Lecture Notes 5 (Erzeng Xue)
Chemical bondings

• An atom can have several shells of electrons,
  spinning around nucleus (n1, 2, 3 etc)
• There is a maximum number of electrons each shell
  can hold
• Electrons at each shell has different level of
  energy, those at outer shell having higher energy
• When excited (absorb energy) an electron can jump
  from lower orbital to higher orbital, which is
  unstable - the electron then jumps back to its
  original orbital and release energy in various
  forms (spectroscopes)

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Electronic Configuration and Periodic Table of
Elements
CH4751 Lecture Notes 5 (Erzeng Xue)
Chemical bondings

• Electronic configuration-distribution of
  electrons among each shell of an atom
• Different elements have different electronic
  configurations
• Periodic Table and Electronic configuration
• The row (period) number rows corresponding to
  the number of shells
• The columns (group) generally representing the
  number of electrons at outer shell

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Electronic Configurations of Elements
CH4751 Lecture Notes 5 (Erzeng Xue)
Chemical bondings

• Element Atomic number Electrons in each shell
  Electron configuration
• n1 n2 n3 n4
• Hydrogen 1 1 1s1
• Helium 2 2 1s2
• Lithium 3 2 1 1s2, 2s1
• Beryllium 4 2 2 1s2, 2s2
• Boron 5 2 3 1s2, 2s2, 2p1
• Carbon 6 2 4 1s2, 2s2, 2p2
• Nitrogen 7 2 5 1s2, 2s2, 2p3
• Oxygen 8 2 6 1s2, 2s2, 2p4
• Fluorine 9 2 7 1s2, 2s2, 2p5
• Neon 10 2 8 1s2, 2s2, 2p6
• Sodium 11 2 8 1 1s2, 2s2, 2p1, 3s1
• Magnesium 12 2 8 2 1s2, 2s2, 2p1, 3s2
• Aluminium 13 2 8 3 1s2, 2s2, 2p1, 3s2, 3p1
• Silicon 14 2 8 4 1s2, 2s2, 2p1, 3s2, 3p2
• Phosphorus 15 2 8 5 1s2, 2s2, 2p1, 3s2, 3p3
• Sulphur 16 2 8 6 1s2, 2s2, 2p1, 3s2, 3p4
• Chlorine 17 2 8 7 1s2, 2s2, 2p1, 3s2, 3p5

shell number n1,2,3,4 etc
type of orbital s,p,d,f
number e-s in that orbital
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Chemical Bonding and e-1 Configurations
CH4751 Lecture Notes 5 (Erzeng Xue)
Chemical bondings

• General Rule of bond formation
• Atoms of an element participating in bonding
  usually try to achieve a closed outer shell (low
  energy) e- configuration as a result of bond
  formation
• e.g.'s Li (1s2 2s1) prefers to be Li (1s2)
  by losing 1 electron
• Mg (1s2 2s2 2p6 3s2) prefers to be Mg2 (1s2
  2s2 2p6) by losing 2 electrons
• F (1s2, 2s2, 2p5) prefers to be F- (1s2 2s2
  2p6) by gaining 1 electron
• Simple Representations of Chemical Bonds
  Electron-Dot (Lewis Structures)
• Rules
• outer shell e- 's only
• element symbol represents "core
• single dots on each side, then pair to a maximum
  of 8, exception He
• Note only works for elements with a max. of 8 e-
  's in outer shell (i.e. not suitable for d
  orbitals)
• e.g. Mg, electron configuration 1s2, 2s2, 2p6,
  3s2 Lewis structure Mg

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Ionic Bonding
CH4751 Lecture Notes 5 (Erzeng Xue)
Chemical bondings

• Involves complete transfer of e- '(s) from one
  atom to the other.
• How many e- 's transfer ?
• Depends on
• number required to leave a filled outer shell
• energy considerations (ionisation vs. bond
  formation)
• Electrostatic forces are involved (attraction of
  opposite charges).
• Consider formation of sodium chloride, NaCl
• Nao Clo NaCl-
• 1s2,2s2,2p6,3s1 1s2,2s2,2p6,3s2,3p5
  (1s2,2s2,2p6) (1s2,2s2,2p6,3s2,3p6)-
• closed shell e- configurations
• Electron-Dot representation
• Na . . Cl Na Cl -

.. ..
.. ..
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Covalent Bonding
CH4751 Lecture Notes 5 (Erzeng Xue)
Chemical bondings

• Involves sharing of outer shell e- '(s) between
  atoms, allowing each atom to have a full shell
  of electrons
• Driving force same as for ionic case overall
  decrease in energy of system i.e. energy is
  evolved during bond formation
• A pair of shared e-s form a single covalent bond
  (2 pairs of shared e-s form a double covalent
  bond, 3 pairs form triple bond)
• Most of gas molecules are covalent bonded
• e.g. hydrogen
• H . . H H H (1 pair shared e-s, single
  covalent bond, written as H-H or H2)
• oxygen
• O O OO (2 pairs shared e-s, double
  covalent bond written as OO or O2)
• Note In electron dot structures of covalent
  molecules, shared electrons placed between
• symbols, electrons which are not
  shared are retained beside symbol for that atom.

.. ..
.. ..
. .
. .
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More Examples
CH4751 Lecture Notes 5 (Erzeng Xue)
Chemical bondings

• Ionic bonding
• Cao 2 Clo
  CaCl2
• 1s22s22p63s23p64s2 1s22s22p63s23p5
  1s22s22p63s23p6 1s22s22p63s23p6
• (Ca2) (Cl-)
• Closed shell e- configuration
• Electron Dot
• Ca .Cl . Cl Ca2 Cl -
  Cl - (Calcium chloride CaCl2)
• Covalent bonding
• N0 N0 N2
• Electron dot . N . . N . NN N º
  N
• 3 pairs of electrons shared
  forming a triple bond

.. ..
.. ..
.. ..
.. ..
..
..
.. .
.. .
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Dative Bonding
CH4751 Lecture Notes 6 (Erzeng Xue)
Chemical bondings

• It is a special type of covalent bond - the pair
  of e-s shared are supplied by one of the
  constituent atoms (instead of supplied by both
  atoms)
• Example NH3 H NH4
• H H
• H N H H N H
• H (hydrogen ion, lost e-) H
• The driving force is the desire to complete the
  1s orbital of hydrogen

.. ..
.. ..
these pair of e-s are supplied by N atom
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Summary of Chemical Bondings
CH4751 Lecture Notes 6 (Erzeng Xue)
Chemical bondings

• Summary so far
• In a chemical bond, atoms or ions are strongly
  attached to one another
• Use of Electron-Dot or Lewis structures
• Ionic bonding
• involves complete transfer of electrons from one
  atom to the other
• e.g. NaCl
• (metal with a low ionisation energy, non-metal
  with a high electron affinity)
• Covalent bonding
• Involves sharing of outer shell e- 's between
  atoms.
• Depending on the number pairs of shared e-s, it
  can be a single covalent bond (e.g. H2, single
  pair of e- 's ), double (O2) and triple bonds
  (N2).
• Dative (coordinate covalent) bond - shared e-s
  supplied from one atom

43
Electronegativity and Bond Polarity
CH4751 Lecture Notes 6 (Erzeng Xue)
Chemical bondings

• In the cases of H2, O2 and N2, the constituent
  atoms in molecule are the same, the shared e-s
  form shell that is symmetry
• When the constituent atoms are different, because
  the force attracting e-s may be different, as a
  result of it the shell will be non-symmetry -
  polar covalent bond.
• e.g. HCl Ho Clo HCl
• (1s1) (...3s23p5)
• Chlorine attracts e-s more strongly than
  hydrogen
• Bonding in HCl is intermediate between ionic
  covalent since e-s are not evenly shared.
• Electronegativity ability of an atom in a
  molecule to attract electrons to itself
• Related to electron affinity and ionisation
  energy, which vary with atoms
• A highly electronegative atom has
• a very negative electron affinity, i.e. it
  attracts electrons from other atoms
• a high ionisation energy, i.e. it resists having
  its own e-s attracted away to other atoms
• The different atoms have different
  electronegativity. Trend in the Periodic Table
• Increase from left to right
• decrease down a group

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Electronegativity and Bond Polarity
CH4751 Lecture Notes 6 (Erzeng Xue)
Chemical bondings

• A value is assigned to each atom for its
  electronegativity. The higher the number is the
  more electronegativity is.
• The difference in electronegativity of atoms in a
  molecule can be used to predict the type of
  bonding between them - the higher difference,
  more polar the molecule.
• Examples
• F2 Electronegativity difference
  4.0(F)-4.0(F)0 Þ Nonpolar covalent bond
• HF Electronegativity difference
  4.0(F)2.1(H)1.9 Þ Polar covalent bond (H? F?-)
• LiF Electronegativity difference
  4.0(F)1.0(Li)3.0 Þ Ionic bond (Li F-)
• Exercises 1. Which bond is more polar? B-Cl or
  C-Cl
• B-Cl EN Diff 3.0(Cl)-2.0(B)1.0
• C-Cl EN Diff 3.0(Cl)-2.5(C)0.5 Answer B-Cl
  bond is more polar
• Exercises 2 Which bond is most polar? S-Cl,
  Se-Cl or Se-Br?
• S-Cl EN Diff 3.0(Cl)-2.5(S) 0.5
• Se-Cl EN Diff 3.0(Cl)-2.4(Se)0.6
• Se-Br EN Diff 2.8(Cl)-2.4(Se)0.4 Answer
  Se-Cl bond is most polar

45
More about Bond Polarity
CH4751 Lecture Notes 6 (Erzeng Xue)
Chemical bondings

• The electronegative difference of the constituent
  atoms makes a molecule polar
• Many properties of substances are related to the
  polarity of molecules through the electrostatic
  force generated by the polarity
• The extend of polarity of molecules can be
  quantified by using dipole moment, which is the
  product of charge multiplying by distance.
• Some other terms frequently encountered when
  talking about bond
• Bond length - the distance between bonding atoms
• Bond strength - how strong the bonding atoms can
  be held by the bond
• Bond angle - geometrical orientation of bonds
  when an atom forming more than one bonds with
  surrounding atoms

e.g. the positive end attracts negative end
resulting in an ordered arrangement or specific
affinity between substances
positive end
negative end
46
Periodic Table of Elements
CH4751 Lecture Notes 6 (Erzeng Xue)

• Originally proposed by Mendeleev in 1869
  according to the atomic weights as well as the
  periodic features of element in their physical
  chemical properties.
• Modern P.T is arranged according to electronic
  configuration of elements.
• Rows (one row per principle quantum level of
  shell)
• Column (group) the elements having the same outer
  e-s.

47
More about Periodic Table of Elements
CH4751 Lecture Notes 6 (Erzeng Xue)

• Metal and non-metals
• metals left and middle (except hydrogen)
• metalloid
• non-metal

• Main groups 1A to 8A
• group 1A Alkali metals e.g. Na
• group 2A Alkaline earth metals e.g. Mg
• group 7A Halogens e.g. Cl
• group 8A Noble gases e.g. Ne
• Group 1B to 8B - transition elements

48
More about Periodic Table of Elements
CH4751 Lecture Notes 6 (Erzeng Xue)

• Many other properties of elements show periodic
  feature. Some examples
• Atomic radius (distance between the nuclei of
  atoms in a chemical bond)
• Decrease from left to right within a row and
  increase from up to down in a group
• First ionisation energy (energy required to
  remove the first e- from a neutral atom)
• Increase from left to right within a row and
  decrease from up to down in a group
• Electron affinity (energy change associated with
  the addition of an e- an atom)
• Increase from left to right within a row and
  decrease from up to down in a group
• Electronegativity
• Increase from left to right within a row and
  decrease from up to down in a group
• etc.