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    • 02 The nature of matter >
      • 0201 Atoms: Building blocks
      • 0202 Classification of matter
    • 05 Chemical reaction, chemical equations >
      • 0500 Overview, preview
      • 0501 Amount of substance, mole
      • 0502 Avogadro constant: How many?
      • 0503 Avogadro constant: Why that number?
      • 0504 Chemical formulas: What do they mean?
      • 0505 What can equations tell us?
      • 0506 Limiting reactants
    • 09 Solutions >
      • 0901 What is a solution?
      • 0902 Miscibility of liquids
      • 0903 Like dissolves like?
      • 0905 Dissolution of ionic salts in water
      • 0906 Can we predict solubilities of salts?
      • 0907 Solution concentration
      • 0908 Chemical species, speciation
      • 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
    • 11 Dynamic chemical equilibrium >
      • 1100 Equilibrium: An overview
      • 1101 Visualising dynamic equilibrium
      • 1102 The jargon of equilibrium
      • 1103 Equilibrium constants
    • 22 Evidence from spectroscopy >
      • 2200 Overview, preview
      • 2201 Spectroscopy: Quantization of energies
      • 2202 Light: Wave-particle "duality"
      • 2203 UV-Visible spectroscopy
      • 2204 Beer's law
    • 27 Communicating chemistry >
      • 2700 Overview, preview
      • 2703 The jargon we use
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    • T01 Communicating chemistry
    • T02 Beer's law
    • T03 Professional amnesia of the chemistry teaching professio
    • T04 Law of equilibrium
    • T05 Visusalizing dynamic chemical equilibrium
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0202 Classification of matter

3/4/2019

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Categorisation of stuffs with common characteristics

Why do we classify stuffs?
​

KEY IDEAS

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 members 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, or explain (or influence) 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”.
​
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:



Picture

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


Picture
There are more 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
  • 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. ……..
  • Electrical conductors vs. non-conductors (insulators)
and many, many more.
​
Remember that classifications are human constructions: they are simply devices decided by people in order to assist description or definition of patterns of behaviours in some way that suits a purpose.

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).



​
SELF 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
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  • Home
  • Modules
    • 02 The nature of matter >
      • 0201 Atoms: Building blocks
      • 0202 Classification of matter
    • 05 Chemical reaction, chemical equations >
      • 0500 Overview, preview
      • 0501 Amount of substance, mole
      • 0502 Avogadro constant: How many?
      • 0503 Avogadro constant: Why that number?
      • 0504 Chemical formulas: What do they mean?
      • 0505 What can equations tell us?
      • 0506 Limiting reactants
    • 09 Solutions >
      • 0901 What is a solution?
      • 0902 Miscibility of liquids
      • 0903 Like dissolves like?
      • 0905 Dissolution of ionic salts in water
      • 0906 Can we predict solubilities of salts?
      • 0907 Solution concentration
      • 0908 Chemical species, speciation
      • 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
    • 11 Dynamic chemical equilibrium >
      • 1100 Equilibrium: An overview
      • 1101 Visualising dynamic equilibrium
      • 1102 The jargon of equilibrium
      • 1103 Equilibrium constants
    • 22 Evidence from spectroscopy >
      • 2200 Overview, preview
      • 2201 Spectroscopy: Quantization of energies
      • 2202 Light: Wave-particle "duality"
      • 2203 UV-Visible spectroscopy
      • 2204 Beer's law
    • 27 Communicating chemistry >
      • 2700 Overview, preview
      • 2703 The jargon we use
  • TOC
  • Index
  • Teachers' area
    • T01 Communicating chemistry
    • T02 Beer's law
    • T03 Professional amnesia of the chemistry teaching professio
    • T04 Law of equilibrium
    • T05 Visusalizing dynamic chemical equilibrium
  • Aha! Whatever
    • Playful dolphins
    • The University of Western Australia
    • Kings Park
  • Prof Bob?
    • Family
    • Travel
    • Perth
    • At work
  • Travelling
  • Contact
  • Blog
  • In four days for two days