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CHEM115 The Molecular World-OPEN University
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Open University
S205_2 20 Hours
Intermediate
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Course Description
This unit will provide you with a detailed
understanding of some of the important problems and topics that are
being studied by the chemists of today, and of the ways in which
associated problems might be solved by chemical methods. But to acquire
this understanding you must have a good grasp of fundamental chemical
ideas, which in this unit are covered under seven main headings and an
overview. Each of those headings consists of a general idea that is of
great importance to chemists. We begin with the idea that comes closest
to defining the nature of chemistry itself.
After studying this unit you
should be able to:
- explain what is meant by
isotopes, atomic numbers and mass numbers of the atoms of chemical
elements by referring to the Rutherford model of the atom;
- give an example of how differences in the molecular
structures of chemical compounds give rise to differences in macroscopic
properties;
- given a Periodic Table,
point to some sets of elements with similar chemistry and to others in
which there are progressive trends in chemical properties;
- indicate ways in which the chemical periodicity
represented by a Periodic Table matches the periodicity in the
electronic structure of atoms;
- use the
Lewis structures of one or two simple chemical substances to illustrate
the ideas of the octet rule, the electron-pair bond and the
valence-shell repulsion theory of molecular shape;
- select a set of organic molecules, each of which
contains the same functional group, and use its reactions to show why
the functional group concept is useful;
- give an example of how the shape of a molecule can
effect its rate of reaction;
- by
referring to the three-way catalytic converter in a motor car, explain
what is meant by a catalyst and distinguish the separate influences of
the rate of reaction and the equilibrium contstant on the progress of a
chemical reaction.
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Introduction
 Introduction
Resource- This unit will provide you with a
detailed understanding of some of the important problems and topics that
are being studied by the chemists of today, and of the ways in which
associated problems might...
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1 Everything that you can see is made of
atoms
- 1.1 Introduction Resource
- The idea that everything that we
can see is an assembly of tiny particles called atoms is chemistry's
greatest contribution to science. There are about 120 known kinds of
atom, and each one is distinguished...
- 1.2 Chemical elements Resource
- Atoms of the same atomic number
behave virtually identically in chemical reactions. They are therefore
given the same chemical name and chemical symbol. For example, the atom
of atomic number 6, which...
- 1.3 Chemical compounds Resource
- Chemical elements contain atoms of
the same atomic number. But most materials consist of chemical
compounds. These are a combination of the atoms of two or more chemical
elements. Such combinations often...
- 1.4 Molecular substances Resource
- Chlorine, bromine and iodine
belong to a family of elements called the halogens. At room temperature,
chlorine (Figure 2e) is a gas, bromine (Figure 2d) is a liquid and
iodine is a dark-purple solid. All...
- 1.5 Non-molecular substances Resource
- Non-molecular substances defy
attempts to pick out discrete molecules from their structures. One
example is common salt, NaCl, which is built up from the tiny cubes
shown in Figure 10a. Look first at the...
- 1.6 Binding forces in molecular and
non-molecular substances – a first look
Resource
- As we shall see in Section 4,
elementary bonding theories imply that materials as different as salt,
iodine and aluminium are held together by different types of chemical
bond. However, all binding forces...
- 1.7 Summary of Section 1 Resource
- All materials are made of atoms of
about 120 different chemical elements, each element being characterised
by an atomic number which lies in the range 1–120.
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2 Chemical patterns are to be found in the
periodic table
- 2.1 Chemical periodicity Resource
- The chemistry of the elements is
immensely varied. But amidst that variety there are patterns, and the
best known and most useful is chemical periodicity: if the elements are
laid out in order of atomic...
- 2.2 The Group number of the noble
gases Resource
- In Figure 18, the Period numbers
increase steadily from 1 to 7 down the columns. It obviously seems
appropriate that the Group numbers should show a similar steady increase
from I to VIII across the rows....
- 2.3 Elements on parade: an
audiovisual interlude Resource
- Here you have the opportunity of
viewing seven video sequences which show both reactions and properties
of some chemical elements. The seven sequences provide examples of the
way in which Periodic Tables...
- 2.4 Summary of Section 2 Resource
- The typical elements can be
displayed in a mini-Periodic Table of eight Groups and seven Periods
(Figure 18). The Periods are numbered from 1 to 7 and the Groups are
labelled I-VIII.
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3 Chemistry can often be explained by
electronic structure
- 3.1 Introduction Resource
- Section 2 used some simple
examples to illustrate chemical periodicity. But how can we explain such
periodicity? The answer lies in the way that the electrons in atoms are
arranged about the positively...
- 3.2 The electronic configurations of
atoms Resource
- The quantum theory of the atom
tells us that we cannot say exactly where an electron in an atom will be
at any particular moment; we can speak only of the probability of
finding an electron at a particular...
- 3.3 Electronic configurations and
the Periodic Table Resource
- Figure 21 has been designed for
use in a particular thought experiment. The purpose of the thought
experiment is to see how the electronic configuration of the atoms
changes as one moves through...
- 3.4 Outer electronic configurations
and the Periodic Table Resource
- The essential message of Figure 22
is that the Groups of elements that appear in columns of the Periodic
Table usually have atoms with similar outer electronic configurations.
Figure 23 incorporates these...
- 3.5 Electron states and box diagrams Resource
- So far, we have represented the
electronic state of an atom as a collection of sub-shells. Now we turn
to the states of the electrons within those sub-shells. Just as shells
can be broken down into sub-shells,...
- 3.6 Summary of Section 3 Resource
- The electronic configuration of an
atom can be obtained by allocating its electrons to s, p, d and f
sub-shells in the order given by Figure 21. This procedure generates a
periodicity in electronic configuration...
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4 Chemical bonds consist of shared pairs of
electrons
- 4.1 Introduction Resource
- Simple theories of chemical
bonding are based on the idea of the electron-pair bond, and the extent
to which the electron pair is shared between the bound atoms. There is
also an assumption that the electronic...
- 4.2 Ionic and covalent bonding Resource
- We begin by applying simple
bonding theories to molecular chlorine gas (Cl2) and non-molecular
sodium chloride (NaCl), whose structures were discussed in Section 1.
Figure 28 shows the result.
- 4.4 Metallic bonding Resource
- Two familiar properties of metals
point to a simple model of metallic bonding. Firstly, metals have a
strong tendency to form positive ions. Thus, when sodium reacts with
water, and when magnesium and...
- 4.4 A classification of chemical
substances Resource
- We now have a provisional but
useful classification of chemical substances. First they are divided
into molecular and non-molecular types, largely on the basis of their
structures. Then a further division...
- 4.5 More about covalent bonding Resource
- So far, the valencies in Table 1
have just been numbers that we use to predict the formulae of compounds.
But in the case of covalent substances they can tell us more. In
particular, they can tell us how...
- 4.6 Summary of Section 4 Resource
- The chemical formulae of many
substances can be understood by arguing that their atoms attain noble
gas structures by chemical combination.
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5 Molecular reactivity
- 5.1 Molecular reactivity is
concentrated at key sites Resource
- Reactivity is not spread evenly
over a molecule; it tends to be concentrated at particular sites. The
consequences of this idea are apparent in the chemistry of many
elements. However, in organic chemistry,...
- 5.2 Summary of Section 5 Resource
- The structural formulae of organic
molecules can be divided into the carbon-hydrogen framework or
skeleton, and the functional group(s). In the first approximation, the
functional groups are the sites...
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6 Molecular shape affects molecular
reactivity
- 6.1 Introduction Resource
- Structural formulae of, for
example, hexan-1-ol (Structure 6.1) and PF5 (Structure 5.13) merely tell
us the immediate neighbours of any particular atom. They are
two-dimensional drawings, which ignore...
- 6.2 The shapes of some molecules Resource
- Here we shall look at the shapes
of some simple molecules of the typical elements. In doing so, we shall
meet the problem of representing three-dimensional shapes on
two-dimensional paper. Let's use methane,...
- 6.3 Valence-shell electron-pair
repulsion theory Resource
- The theory of molecular shape that
we have been working towards is called valence-shell electron-pair
repulsion theory (VSEPR theory). When applied to molecules and ions of
the typical elements, its success...
- 6.4 Summary of Section 6 Resource
- Molecules have a three-dimensional
shape. Bulky irregularities in the shape of a molecule around a
reactive site can exclude a potential reactant. Such effects are
described as steric.
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7 Reactivity needs a favourable rate and
equilibrium constant
- 7.1 Introduction Resource
- So far, we have concentrated on
the electronic and spatial structures of chemical substances, but we
have not said much about chemical reactions. Now we turn to the question
of why chemical reactions happen....
- 7.2 Is the equilibrium position
unfavourable? Resource
- The first possibility is that the
reaction system has been able to reach chemical equilibrium, but the
equilibrium position is not favourable. How does this come about? If
equilibrium has been reached,...
- 7.3 Is the rate of reaction very
slow? Resource
- If the equilibrium position is
very favourable, then the reason why Reaction 8.1 fails to occur at 525
°C must be that its rate is very slow. Usually, a reasonable response
would be to increase the temperature...
- 7.4 Equilibrium positions and rates
of reaction in this unit Resource
- Section 7 showed that if a
reaction is to occur at a particular temperature, two conditions must be
fulfilled: its equilibrium constant must be sufficiently large, and its
rate sufficiently great. We finish...
- 7.5 Summary of Section 7 Resource
- The equilibrium constant of a
reaction is fixed at any particular temperature. It depends only on the
natures of the initial reactants and the final products; what happens as
reactants change into products...
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8 Reviewing and reflecting
- 8 Reviewing and reflecting Resource
- Figure 55 is a conceptual diagram
that summarises this unit. Molecules are made of atoms, so it was with
atoms, to the left of Figure 55, that we began. Early in Section 1 they
acquired a structure...
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References and Acknowledgements
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Copyright 2007,
by the Contributing Authors.
Cite/attribute Resource.
administrator. (2010, January 30). CHEM115 The Molecular World-OPEN University. Retrieved March 11, 2010, from Free University Courses OCW Courses OpenCourseWare Freeversity Foundation Web site: http://freeversity.org/science-and-mathematics/chemistry/chem115-the-molecular-world-open-university.
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