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    • Chapter 02 Stuff, matter: What is it? >
      • 0200 Stuff, matter: A theory of atoms
      • 0201 Atoms: The building blocks of all stuff
      • 0202 People classifying stuffs. Why?
    • Chapter 05 Chemical reactions, chemical equations >
      • 0500 Chemical reactions vs. chemical equations. Overview
      • 0501 Chemical amount and its unit of measurement, mole
      • 0502 The Avogadro constant: How many is that?
      • 0503 The Avogadro constant: Why is it that number?
      • 0504 Chemical formulas: What can they tell us??
      • 0505 Chemical equations: What can they tell us?
      • 0506 Limiting reactants: How much reaction can happen?
      • 0507 Balanced chemical equations: What are they?
      • 0508 Chemical reactions as competitions
    • Chapter 09 Aqueous solutions >
      • 0901 What is a solution? And what is not?
      • 0902 Miscibility of liquids in each other
      • 0903 Like dissolves like? Shades of grey
      • 0905 Dissolution of ionic salts in water: A competition
      • 0906 Can we predict solubilities of salts?
      • 0907 Solution concentration
      • 0908 Chemical species, speciation in aqueous solution
      • 0909 Solutes: Electrolytes or non-electrolytes?
      • 0910 Electrolytes - strong or weak?
      • 0911 Concentrated, dilute, strong, weak
      • 0912 Species concentration vs. solution concentration
      • 0913 Weak electrolytes: Getting quantitative
    • Chapter 11: Dynamic chemical equilibrium >
      • 1100 Dynamic chemical equilibrium: Overview
      • 1101 Visualising dynamic chemical equilibrium
      • 1102 The jargon of chemical equilibrium
      • 1103 Equilibrium constants: The law of equilibrium
      • 1104 The law of equilibrium: an analogy
    • Chapter 22 Spectroscopy >
      • 2200 Spectroscopy: Overview and preview
      • 2201 Quantisation of forms of energy
      • 2202 Light: Wave-particle "duality"
      • 2203 Ultraviolet-visible spectroscopy
      • 2204 Beer’s law: How much light is transmitted?
    • Chapter 27 The greenhouse effect, climate change >
      • 2700 The greenhouse effect: overview
      • 2701 Is Earth in energy balance?
      • 2702 CO2 in the atmosphere before 1800
      • 2703 So little CO2! Pffft?
      • 2704 Does CO2 affect Earth's energy balance?
      • 2705 The "greenhouse effect"
      • 2706 Why does CO2 absorb radiation from Earth?
      • 2707 The "enhanced greenhouse effect"
      • 2708 Why doesn't CO2 absorb the radiation from the sun?
      • 2709 Why are N2 and O2 not greenhouse gases?
      • 2710 Doesn't water vapour absorb all the IR?
      • 2711 Carbon dioxide from our cars
      • 2712 The source of energy from combustion
      • 2713 Comparing fuels as energy sources
      • 2714 Methane: How does it compare as a GHG?
      • 2715 Different sorts of pollution of the atmosphere
      • 2716 "Acidification" of seawater
    • Chapter 27 Communicating chemistry >
      • 2700 Overview, preview
      • 2703 The jargon we use
  • TEACHERS' CORNER
    • T01 Communicating chemistry
    • T02 Beer's law
    • T03 Professional amnesia of the chemistry teaching professio
    • T04 Law of equilibrium
    • T05 Visusalizing dynamic chemical equilibrium
    • Information vs. knowledge
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0202 People classifying stuffs: Why?

4/3/2019

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​Module 0202

​​

People classifying stuffs: Why?



​​Classification of matter

Why do we classify stuffs? Using which criteria?

   Stuffs with common characteristics, stuffs that are different    (in which properties?)

​Different strokes for different folks


​

Preamble: Is chemistry about stuffs?

Or about people doing and thinking about stuffs?


During your time learning Chemistry, you may have read something like: “Matter is classified in the following way: …[description here]…...”. Prof Bob has two concerns about this. First, this sounds almost as though each stuff inherently “belongs” in a certain category - as though categorised by Mother Nature.

No, things don’t exist in categories independently of people: people assign them into categories. Secondly, … Into which categories, according to which criteria? There may be many different ways that people can categorise the same stuffs – depending on the usefulness of allocating according to particular characteristics of the stuffs.
 
So, let’s try again, showing classification to be an active process: “People can allocate stuffs in a number of ways, depending on which characteristics are useful for a particular purpose. One of the possible ways of classifying stuffs is the following: .................... ”.
​

Watch Prof Bob and Aussie talk about it ....
Prof Bob discusses with Aussie ways in which people can, and do, classify stuffs.
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KEY IDEAS - People classifying stuffs: Why?
Picture
Can we have some order, please!


​Why do we classify?


​Classification is the allocation of different objects to different groups (called classes) for the purposes of generalisation about the properties of members in each class, or to distinguish between the properties of stuffs in different classes.

Although the properties of every member of a population (like people, plants, animals, transport systems, ways of thinking, ……….) are unique and important, to try to understand the behaviour of every individual can be an impossible task.

We try to reduce the complexity by allocating the objects to various classes such that the commonalities among members of any one class are sufficiently similar for us to make generalisations about their properties.

Members may belong to more than one class: for example, a person may belong to the class “Female”, and to the class “Blonde”, as well as to the class “Aged 15 to 25”.
​


Classification in chemistry


In the field of chemistry, classification of materials (stuffs) is used to clarify the meaning of some basic concepts related to matter (anything which has mass and occupies volume of space). This can be done by using a Venn diagram to show relationships, such as in the following example:
​


Picture

​Another way of showing these relationships among classes, sub-classes and sub-sub-classes is the following flow diagram:

Picture
There are other obvious characteristics (properties) that we can use to classify stuffs. These include, for example:
  • Solids vs. liquids. vs. gases (at room T and p)
  • White vs. red vs. green vs. ……
  • Soluble in water vs. insoluble in water (See Module 0901 and Module 0905)
  • Mixtures that are solutions vs. mixtures that are not (See Module 0901)
  • Ionic compounds vs. covalent molecular compounds vs. covalent network compounds
  • Organic compounds vs. inorganic compounds
  • Oxidising agents vs. reducing agents
  • Acidic substances vs. alkaline substances vs. neutral substances
  • Group 1 elements of the periodic table vs. Group 2 elements vs. ……..
  • Solutes which are electrolytes vs. those that are non-electrolytes (See Module 0909)
and many, many more.
​

​

Classification - a human construct

Different purposes. Shades of grey.


​Remember, when you are learning Chemistry, that classifications are human constructions: they are simply devices decided by people in order to assist understanding of patterns of behaviour - in some way that suits a purpose. In particular, they help our learning chemistry by allowing us to focus on commonalities, rather than on the specific details of each stuff - although the more expert you might become, the more important are the details. Remember too that classification can help to demonstrate the differences (not just the similarities) between characteristics of stuffs.

The dividing line between classes (Which materials are this class, and which are in that class?) is sometimes not definite, and can be allocated differently by different people. This is the case with the classifications metal vs. non-metal vs. semi-metal (metalloids). Depending upon the criteria used to classify materials, the dividing lines (that govern which materials “belong” in each class) can vary.



External reference
For further discussion of this subject, and clarification of the meanings of the concepts referred to in the Venn diagram above, see …….
​Mahaffy, P.G., Bucat, B., Tasker, R., and others. “CHEMISTRY: Human Activity, Chemical Reactivity” (Nelson Education), Section 2.2 Classifying Matter, pages 20-23 (both International and Canadian editions).



​
Picture

SELF CHECK: Some thinking tasks

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Are you all sorted? Check ....
1. Into a copy of the Venn diagram shown above, put the following materials into their appropriate classes:
  • vinegar
  • sodium chloride
  • chlorine
  • concrete
  • water
  • sea water
  • milk
  • gold
  • mud
  • air
​
2. Which stuff am I?
  • I am in the class of materials called pure substances.
  • I am in the class of materials called gases.
  • I am in the class of materials considered to be composed of molecules
  • I am in the class of materials called elements.
  • I am in the class of materials that are green.
  • I am in the class of materials called the Group 17 elements of the periodic table.
​
3. Which stuff am I?
  • I am in the class of materials called mixtures.
  • I am in the class of materials that are homogeneous. Therefore, I am a solution.
  • I am in the class of materials called gases.
  • I am in the class of materials essential for life.
  • The main component of the mixture is nitrogen molecules, and the next most is oxygen molecules.
​
Answers (No peeking until you have made a commitment to an answer, in each case.

​1.
Picture

2.  Chlorine gas, Cl2(g)

​3.  Air
Picture

LEARNING CHEMISTRY FOR UNDERSTANDING

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  • HOME
  • NAVIGATION
    • Table of contents
    • Index
    • TALK WITH PROF BOB?
  • LEARNING MODULES
    • Chapter 02 Stuff, matter: What is it? >
      • 0200 Stuff, matter: A theory of atoms
      • 0201 Atoms: The building blocks of all stuff
      • 0202 People classifying stuffs. Why?
    • Chapter 05 Chemical reactions, chemical equations >
      • 0500 Chemical reactions vs. chemical equations. Overview
      • 0501 Chemical amount and its unit of measurement, mole
      • 0502 The Avogadro constant: How many is that?
      • 0503 The Avogadro constant: Why is it that number?
      • 0504 Chemical formulas: What can they tell us??
      • 0505 Chemical equations: What can they tell us?
      • 0506 Limiting reactants: How much reaction can happen?
      • 0507 Balanced chemical equations: What are they?
      • 0508 Chemical reactions as competitions
    • Chapter 09 Aqueous solutions >
      • 0901 What is a solution? And what is not?
      • 0902 Miscibility of liquids in each other
      • 0903 Like dissolves like? Shades of grey
      • 0905 Dissolution of ionic salts in water: A competition
      • 0906 Can we predict solubilities of salts?
      • 0907 Solution concentration
      • 0908 Chemical species, speciation in aqueous solution
      • 0909 Solutes: Electrolytes or non-electrolytes?
      • 0910 Electrolytes - strong or weak?
      • 0911 Concentrated, dilute, strong, weak
      • 0912 Species concentration vs. solution concentration
      • 0913 Weak electrolytes: Getting quantitative
    • Chapter 11: Dynamic chemical equilibrium >
      • 1100 Dynamic chemical equilibrium: Overview
      • 1101 Visualising dynamic chemical equilibrium
      • 1102 The jargon of chemical equilibrium
      • 1103 Equilibrium constants: The law of equilibrium
      • 1104 The law of equilibrium: an analogy
    • Chapter 22 Spectroscopy >
      • 2200 Spectroscopy: Overview and preview
      • 2201 Quantisation of forms of energy
      • 2202 Light: Wave-particle "duality"
      • 2203 Ultraviolet-visible spectroscopy
      • 2204 Beer’s law: How much light is transmitted?
    • Chapter 27 The greenhouse effect, climate change >
      • 2700 The greenhouse effect: overview
      • 2701 Is Earth in energy balance?
      • 2702 CO2 in the atmosphere before 1800
      • 2703 So little CO2! Pffft?
      • 2704 Does CO2 affect Earth's energy balance?
      • 2705 The "greenhouse effect"
      • 2706 Why does CO2 absorb radiation from Earth?
      • 2707 The "enhanced greenhouse effect"
      • 2708 Why doesn't CO2 absorb the radiation from the sun?
      • 2709 Why are N2 and O2 not greenhouse gases?
      • 2710 Doesn't water vapour absorb all the IR?
      • 2711 Carbon dioxide from our cars
      • 2712 The source of energy from combustion
      • 2713 Comparing fuels as energy sources
      • 2714 Methane: How does it compare as a GHG?
      • 2715 Different sorts of pollution of the atmosphere
      • 2716 "Acidification" of seawater
    • Chapter 27 Communicating chemistry >
      • 2700 Overview, preview
      • 2703 The jargon we use
  • TEACHERS' CORNER
    • T01 Communicating chemistry
    • T02 Beer's law
    • T03 Professional amnesia of the chemistry teaching professio
    • T04 Law of equilibrium
    • T05 Visusalizing dynamic chemical equilibrium
    • Information vs. knowledge
  • PERSONAL GALLERY
    • Family
    • Travel
    • Playful dolphins
    • The University of Western Australia
    • Kings Park
    • Perth
    • At work
    • 999 Thermodynamics