6.3 Valence-shell electron-pair repulsion theory

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 rate is high. Here is a stepwise procedure that you can follow when applying this theory. It is illustrated with the molecule XeF4 and the ion C1O3. Xenon tetrafluoride is one of the select band of noble gas compounds that were unknown before 1962
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3.4 Outer electronic configurations and the Periodic Table

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 configurations into our mini-Periodic Table of typical elements; they appear at the top of each Group. They imply that the typi
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6.3 Where is the complexity and what is it?

When I reflect on my experiences of child-support, I attribute the properties of mess, complex, or hard-to-understand to the situation. So, are mess, complex, and hard-to-understand the same thing? If they are, why is the course called Managing Complexity, rather than, say, Managing Messes? A glib answer is you might not have been attracted to it because of the everyday meaning of mess. Yet another answer is that complexity is a rich term whose everyday meanings have been further enriched by
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4.8 Assess and review again

If you've been following the stages of our problem-solving map, then the chances are you're ahead of me here (Figure 19). Yes, if it works, hurrah; if it doesn't then off we go again, all the way back to ‘possible solutions’ and selecting the best of the rest. Or maybe even going back to the be
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4.7 Build prototype/demonstrator

The physical models we talked about earlier are prototypes or demonstrators of a sort. However, for the purposes of making a clear distinction in the process, I'm referring here to prototypes or demonstrators as functioning preliminary models of the essential finished product or construction or service, bringing together all the elements of the design that may or may not have been previously physically tested (Author(s): The Open University

5.3 Purposeful and purposive behaviour

It is possible, as observers, to ascribe a purpose to what we or others do, the actions we take. How particular actions, or activities are construed will differ from observer to observer because of their different perspectives, which arise from their traditions of understanding. For example, in Author(s): The Open University

5.1 Introduction to key concepts

Before I go any further I will establish the meaning of some of the key concepts that you will encounter throughout this unit.

The key concepts elaborated in this unit are:

  • inventor

  • invention

  • design

  • product champion

  • entrepreneur

  • improver

  • innovation

  • dominant design

  • robust design

  • lean design

  • radical
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2.2 The inventive drive

What events and ideas spurred people to come up with thousands of inventions in the last 100 years?

Ron Hickman was a do-it-yourself enthusiast who damaged a chair being used to support a piece of wood he was sawing. Instead of merely being annoyed at the accident he set about designing and building a prototype of a combined workbench and sawhorse to prevent further damage to his furniture. This became the Workmate (Author(s): The Open University

2.1 Everyday life

Picture an everyday scene. You're in a high street coffee shop. All around you people are drinking coffee. Some people are chatting with friends, others are using their mobile phone. A few individuals seem to be working – consulting their laptop computers, scribbling notes. In a corner of the coffee shop an internet cafe has been set up. At one table a couple of teenagers are laughing at a message in a chat room, while at another table an old chap searches the Web for something.

Now
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5.9.1 Microfiltration

This process removes particles between 0.05 and 5 μm in size. The water is pumped at a pressure of 100–400 kPa through the membrane module.

Microfiltration has been adopted by water companies as a means of removing some stages in the life cycle of the chlorine-resistant pathogens Cryptosporidium and Giardia. It is widely used to produce pure water for the electronics, pharmaceutical, chemical and food industries, by removing microbial cells and small particles.


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5.9 Membrane filtration

Membrane filtration is a process whereby particles smaller than about 10−2 mm (which can pass through sand filters) are removed using synthetic polymeric membranes and a high pressure. The membrane effectively acts as a sieve.

It is increasingly becoming popular as an advanced treatment process for water (especially for removal of Cryptosporidium) and wastewater (where water reuse takes place), and various possibilities are:

  • <
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Acknowledgements

The content acknowledged below is Proprietary (see terms and conditions) and is used under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence.

Unit image

Courtesy of Lanterna at Flickr

All other materials included in this unit are derived from conten
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2.6 Centre and periphery

Here you have considered some of the ways in which the power and authority of the emperor were communicated to the inhabitants of the empire. The full dynamics of the relationship are difficult to reconstruct especially as the view gained is mainly from Rome looking out to the provinces rather than vice versa. It was important for the emperor to appear to be a competent ruler of the empire. It was one method used by his peers and successors to evaluate an emperor's reign. But it is often diff
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Further reading

Berger and Luckmann (1967) is a classic text in the development of the social constructionist perspective within the sociological tradition. Burr (1995) offers a very thorough review of the social constructionist perspective, clearly outlining the methods of discourse analysis. Although the book draws significantly on debates within social psychology, it is of wide relevance to the social sciences more generally.


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3.1 Competing explanations of social problems

If we can agree that poverty is a social problem, we are led to another question: what sort of social problem is it? For some, it is a social problem because people should not be poor: it involves social injustice. For others, poverty is a social problem because poor people behave badly (or bring up children poorly): it involves social disorder. We therefore have another parting of the ways, with some believing that social justice requires poor people to become less poor, and others believing
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Systems thinking: Understanding sustainability
In the increasingly complex world of change and uncertainty, particularly in the context of climate change, the notion of sustainability is often raised as the key issue for decision making in the 21st Century. But 'sustainability' is itself a contentious term and often used in misguided ways, depending on the context of use. This unit introduces ways in which systems thinking can help support processes of decision making among stakeholders with different, often contrasting, perspectives on sust
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1 Why is information security important?

This unit introduces you to information security and its management.

A succinct definition of information security might run as follows:

Information security is the collection of technologies, standards, policies and management practices that are applied to information to keep it secure.

But why is it important to secure information? And how should its security be managed? To s
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4.3 A commercial implementation

In order to conclude this section I shall describe a commercial implementation of an object bus. It has been developed by a company known as SoftWired Ltd and is known as iBus. It is based on TCP/IP rather than UDP. The facilities offered by the iBus API provide developers with the facilities to construct objects which can subscribe to channels and to transmit any Java object to a channel. The code for a transmitter is shown below; the import statements are not shown. In
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5.2.1 Discrete variables

The charts about different modes of transport and that on attendance figures at a range of cultural events all use what might be called ‘word categories’. Each category (e.g. bus, rail, cycle, and walk) is quite distinct from any other in the set of categories. Such distinct categories are known in mathematics as ‘discrete variables’.

Word categories are not the only type of variable that is discrete; numbers can also be discrete. For example, at the beginning of this section, w
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