QUI_01_ Physico-chemical assays of solids
AF Unit 1: Physico-chemical properties of solid substances
1.1 An introduction to kinetic molecular theory
The kinetic molecular theory explains
the behavior of solids, liquids and
gases. Have you ever wondered why
these substances behave so differently?
Look at the image. Why is it possible
for water to be solid, liquid or gas?
What differences do you find between
the microscopic structure of a solid and
a liquid?
Source: es.wikipedia.org
Some of you may remember the answer from previous courses. In case you haven’t heard
about the kinetic molecular theory, go to the following animations that will help you understand
the basics of this important scientific theory. Notice you can activate subtitles in the animation in
case you need it:
Interactive content: Behavior of Matter
Interactive content: The Particle Model
TASK 1: Do the following online tests to check if you understood the kinetic theory.
Test: Behavior of Matter
Test: The Particle Model
TASK 2: You are given sentences that describe the behavior of a substance. You have to
decide if the sentence describes a solid, a liquid or a gas. Then, check your answers with
your partner.





Any attractions between the particles are fairly negligible.
The particles are mainly touching, but some gaps have appeared in the structure.
The particles are touching and the only motion allowed to them is vibration.
The distance between individual particles is of the order of ten times the diameter of the
particles.
The particles are arranged regularly or at random.
QUI_01_ Physico-chemical assays of solids. / Unit 1
1


The particles are entirely free to move.
The particles are almost as close together as they were in a solid.
TASK 3: The following online-tests are a little bit more difficult. Work in pairs and help
each other. Write down your score for each test:
Review quiz: kinetic molecular theory.
Score:_____________.
Practice quiz: kinetic molecular theory. Total points:_____________ out of 15.
1.2 Basics about solid substances
In this formative activity, you will get to know more about solids, liquids and gases. Nevertheless,
you are going to focus your attention on solid substances.
Don’t worry if you don’t understand some English words. You can always check the following
website to translate them into your own language. Be careful with online translators, sometimes
they can make mistakes when translating sentences out of context:
Free online translator
TASK 4: Use the following substitution table to produce three correct sentences about
solids. See the example below:
Solid substances
melt
their molecules are
ordered
Like ionic
chemical
compounds are
crystalline
a quantity of heat is
applied
have a definite
shape




because
its molecules are fixed in
their places by
intermolecular forces
“Solid substances melt because their molecules are ordered”. The sentence is written
taking one part of each of the columns. (by the way, is the sentence in the example
correct?)
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
TASK 5: Check the answers of “task 4” with your partner. Have you written the same
sentences?
QUI_01_ Physico-chemical assays of solids. / Unit 1
2
1.3 Microscopic structure of solid substances
Look at the following image:
Source: cristalchornet.blogspot.com
The image shows two different solid structures. It is important that you are able to distinguish
between these two kinds of solids.
HIGHLIGHTS
On the left side of the image, atoms are located at random positions. These kind of solid
structures are called amorphous. On the right side of the image, atoms are arranged
regularly; these kinds of solids are crystals.
TASK 6: You will work in pairs. The following link takes you to an interesting video in
which you can see different molecular structures of solid substances.
Molecular structures of solid substances
To learn vocabulary about solid structures and understand the difference between
crystalline and amorphous solids, try to complete the following text, which is a
transcription of the video.
Use the following words to fill in the gaps:
glass, repetitive, atoms, structure, sugar; single, crystalline, liquids, interrupted,
melting, bonds, rigidly, solids
QUI_01_ Physico-chemical assays of solids. / Unit 1
3
Remember that you can always use an online translator if you don’t know the meaning of some
of the words.
Free online translator
Crystalline and amorphous solids
There are two main classes of __________, crystalline and amorphous.
Crystalline solids: observe the ____________of the solid displayed on the screen. You can
easily trace the regular _____________pattern of the atoms or the molecules or ions. These
type of solids are called ___________ solids. The crystalline solids have symmetrical shapes
flat smooth and plain faces which meet at a characteristic angle. Crystalline solids are classified
as “single crystals” and “polycrystalline crystals”. If the periodicity of the pattern is extended
throughout the volume of the solid, then the solid is a ___________ crystal. In a polycrystalline
crystal, the periodicity of the pattern is ______________ at de boundaries. Crystalline solids
have a sharp _________ point. All ________ have the same strength in the case of crystals.
Diamond, rock salt, mica and __________ belong to this category.
Amorphous solids: like___________, the atoms and the molecules of amorphous solids are not
arranged in an orderly manner, but the difference between an amorphous solid and a liquid is
that the ________ are __________ fixed and they are not free to move as in liquids. _________
is an amorphous solid.
TO KNOW MORE
Crystalline solids can have different kinds of crystalline structures, depending on how the
molecules or atoms are ordered. Check the following link to learn more about these
structures.
Types of crystals
1.4 Polar and non-polar substances. Solubility.
Molecules can be classified in polar and non-polar. This is important to determine, for instance,
if a solid is soluble in a liquid. As a general rule, remember the following sentences:
HIGHLIGHTS
A general rule is that like dissolves like.
Generally, ionic and polar substances are soluble in polar solvents like water.
Non-polar compounds are normally soluble in non-polar solvents such as carbon
tetrachloride.
TASK 7: Now it’s time to write some questions and test your partner’s knowledge about
solubility and polarity of solvents and solutes. Make groups of two. First of all, read the
following information about solubility:
Solubility. Factors affecting solubility.
QUI_01_ Physico-chemical assays of solids. / Unit 1
4
If you find it difficult to write questions in English, you can use the following language
support:
Language support: Question words:







Who (person)
Where (place)
When (time)
Why (reason)
What (specific thing)
Which (choice)
How (way, manner).
Language support: Question structures. Examples:







What is the definition of….?
Why is “soluble” a relative term?
Is alcohol soluble in…..?
How is the solubility determined?
At what temperature will the ………..….. dissolve?
How many grams of…………….. will solve in ……..?
What is the influence of ……….. in ……………?
Then, prepare a quiz with at least 5 questions about solubility and polarity of solutes and
solvents. Finally, share your quiz with other couples and try to answer quizzes prepared
by your partners. Create the quiz using the following internet resource:
Create your own quizzes!
QUI_01_ Physico-chemical assays of solids. / Unit 1
5