8 Reviewing and reflecting
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 with a positively charged nucleus surrounded by negatively charged electrons. To a chemist, the most important property of an atom is the
6.4 Summary of Section 6 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. A sufficient refinement of the molecular shape in the region of the reactive site can make that site specific to just one particular reactant. Many enzymes operate in this way. The shapes of simple molecules can be predicted using valence-she
4.5 More about covalent bonding 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 the atoms are linked together in the molecule. This information is obtained from a two-dimensional drawing of the structural form
4.3 Metallic bonding 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 aluminium react with acids, hydrogen gas is evolved and the ions Na+(aq), Mg2+(aq) and Al3+(aq), respectively, are formed. Secondly, metals are good conductors of electricity: when a voltage difference is applied
4.1 Introduction 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 structures of noble gas atoms are especially stable, and that many elements try to attain these structures when they react to form chemical compounds. These ideas were the brainchild of the American chemist, G. N. Lewis (Box 3). In developing them, we shall simplify the electronic confi
3.6 Summary of Section 3 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 which matches that of the Periodic Table. The typical elements have
3.5 Electron states and box diagrams 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, so sub-shells can be broken down into atomic orbitals. Each atomic orbital describes an allowed spatial distribution about the nucleus for an electron in the sub-shell. Here we shall only be concerned with their number. Consider the formula for the sub-shell electron capaci
1.4 Molecular substances 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 li
1.3 Chemical compounds 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 occur in simple numerical ratios. Thus, when sodium metal (Figure 2b) and chlorine gas (
1.2.1 Isotopes All atoms of the same element have identical atomic numbers, and are chemically similar, but they may not be identical in other ways. Figure 2f shows copper. All copper atoms have atomic number 29: all their nuclei contain 29 protons. But they also contain uncharged particles called neutrons. In natural copper, the a
1.2 Chemical elements 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 is shown in Figure 1, is a carbon atom, whose symbol is C. All materials are made of atoms, but there is a special class of substan
11 Additional resources Bandolier (2005) Statins: when should you take the tablet? British Red Cross (2007) First aid guidelines in the UK Cardiac Risk in the Young (2003) When a young person dies suddenly Clay, R. A. (2001) Research to the heart of the matter Department of Health (2000) National Service Framework for coronary heart disease, Chapter 4 Department of Health (2007) The coronary heart disease National Service Framework: shaping the future: progress report 2006 The Nat
9 Summary Now you will be very familiar with cardiovascular diseases, their development and their diagnosis. You will also know their treatment and many of the cardiovascular disease risk factors – what they are and how they can be influenced positively to minimise cardiovascular diseases. You will understand the overall importance of a balanced diet, regular exercise and weight management (guided by adiposity measurements) throughout life, to maintain cardiac and vascular health. You will also be a
8.2 Secondary prevention using drugs Extensive research has been carried out into the use of drugs to help limit damage and minimise deterioration of an established heart or circulatory condition. The use of four main drug categories together reduces the risk of an MI, a stroke or cardiovascular disease death over the next two years by 75 per cent in patients with previous coronary heart disease or stroke (2002 figures from Mackay and Mensah, 2004). Such secondary prevention of cardiovascular diseases has been formalised into a
3.2.1 Fats Fats, also known as lipids, are important components of living tissues, and are used by the body for making cell membranes and for storing energy. Fats come in a variety of different biochemical types, which may be obtained from the diet or can be synthesised within the body. Many cells of the body can convert certain types of fat into others, but by preference, fats will be obtained from the diet, if available. The fatty acids that cannot be synthesised by the body and therefore must
2.10.1 Mean and standard deviation for repeated measurements In everyday terms, everybody is familiar with the word ‘average’, but in science and statistics there are actually several different kinds of average used for different purposes. In the kind of situation exemplified by Table 2, the sort to use is the mean
(or more strictly the ‘arithmetic mean’) For a set of measurements, this is de
1 Developing modelling skills The main teaching text of this unit is provided in the workbook below. The answers to the exercises that you'll find throughout the workbook are given in the answer book. You can access it by clicking on the link under the workbook. Click 'View document' to open the workbook (PDF, 0.2 MB). Acknowledgements The content acknowledged below is Proprietary (see terms and conditions) and is used under licence. All materials included in this unit are derived from content originated at the Open University. 5.1 Arithmetic with real numbers At the end of Section 1, we discussed the decimals
4.2 Least upper and greatest lower bounds We have seen that the set [0, 2) has no maximum element. However, [0, 2) has many upper bounds, for example, 2, 3, 3.5 and 157.1. Among all these upper bounds, the number 2 is the least upper bound because any number less than 2 is not an upper bound of [0, 2).
and asked whether it is possible to add and multiply these numbers to obtain another real number. We now explain how this can be done using the Least Upper Bound Property of Author(s):
