Atoms and atomic theory

English in chemistry 1 – 2017 
TS. Nguyễn Tuyết Phương – TS. Trần Thu Phương 
 
 
16 
Q1. Answer the following questions by using the reading text. 
1. For a gas under typical conditions, what approximate percentage of the volume is 
occupied by the gas particles themselves? 
2. Why is it harder to walk through water than to walk through air? 
3. When does the average velocity of the gas particles increase? 
4. What are the key assumptions that distinguish an ideal gas from a real gas? 
5. Which of the following statements is/are true about a gas in a closed container? 
a. When the particles collide, the temperature rises in the container. 
b. When the particles collide, the gas particles change their direction of motion and their 
velocity. 
c. When the particles collide, the temperature and pressure rise in the container. 
 
Q2. - Make groups of students. 
- Each group prepares 5 questions. 
- Each group takes turn to ask and answer questions from the other group. 
Grammar note: 
1. Review of “If clause” 
2. - Because 
+ Clause 
- Because of + Noun phrase 
 
 

English in chemistry 1 – 2017 
TS. Nguyễn Tuyết Phương – TS. Trần Thu Phương 
 
 
17 
Lesson
 6. 
INTERMOLECULAR FORCES: SOLID AND LIQUID
 
6.1 Listening: What are intermolecular forces 
Complete the paragraph by filling the blanks 
 
In this video, you are going to learn what we mean by intermolecular forces that there are 
three common types of intermolecular force and the difference between these three types of 
intermolecular force. 
An intermolecular force is simply an attractive …(1)… between neighboring molecules. 
There are three common types of intermolecular force namely (one) permanent dipole-
dipole forces; (two) hydrogen …(2)…; and (three) van der Waals’ forces. All of these three 
forces are very much weaker than ionic or covalent bonds which …(3)… atoms and ions 
together in elements and compounds. We have a video each on ionic and covalent bonds if 
you haven’t learnt about them yet. 
Let us now look at these three intermolecular forces one by one, first up the …(4)… dipole-
dipole forces. A polar molecule is one in which there is a permanent dipole arising usually 
because the different atoms in the molecule have …(5)… electronegativities, the attraction 
by a bonded atom for the pair of electrons in a covalent bond. Let us take hydrogen chloride 
as an example. Hydrogen chloride is a …(6)… molecule as the pair of electron in the 
hydrogen chlorine bond are nearer to the chlorine atom. In other words, they tend to one 
pole. The chlorine atom has a stronger attraction to the electrons because it has a greater 
electronegativity than the hydrogen atom. We can represent the hydrogen chloride …(7)… 
as H (delta positive) and Cl (delta negative). Thus there will be an attraction between the 
delta negative on the chlorine atom of one molecule and the delta …(8)… on the hydrogen 
atom of a neighboring molecule. The diagram below shows the permanent dipole-dipole 
force between the two molecules of hydrogen chloride indicated here by a red dashed line. 
The second type of …(9)… force is the hydrogen bond. The permanent dipole in a covalent 
bond between a hydrogen atom and a fluorine, oxygen, or nitrogen atom is particularly 
strong, thus the attraction between the electron deficient H delta positive of one molecule 
and the lone pair of electrons on a …(10)…, oxygen, or nitrogen atom of another molecule 
is much stronger than the permanent dipole-dipole attraction mentioned before between the 
two hydrogen chloride molecules. This particular type of dipole-dipole attraction between 
the electron deficient H delta positive of one molecule and the lone …(11)… of electrons on 
a fluorine, oxygen, or nitrogen atom of another molecule is given the special name of 

English in chemistry 1 – 2017 
TS. Nguyễn Tuyết Phương – TS. Trần Thu Phương 
 
 
18 
hydrogen bond. So a hydrogen bond is the attraction between the H delta positive of one 
molecule and the lone pair of electrons on a fluorine, oxygen, or nitrogen atom of a 
…(12)… molecule. Even though a hydrogen bond has only about 5% the strength of a 
covalent bond, it does have a significant effect on the physical properties of compounds. For 
example, were it not for hydrogen bonds both water and alcohol would be …(13)… at room 
temperature and pressure. 
Number three, van der Waals’ forces. Firstly, note the spelling of van der Waals’ forces. It 
is a lowercase “v” in “van” and the apostrophe comes after the s in “Waals”. Van der 
Waals’ forces are induced dipole-dipole interaction. Let’s look at how these arise. They 
arise out of the movement of the electrons in the …(14)…. If we could freeze the action any 
moment in time, there would be an instantaneous dipole at that particular moment. These 
induced dipole-dipole interactions called van der Waals’ forces occur in all molecules 
whether polar or not, but are the only intermolecular forces between …(15)… molecules 
such as the halogens and the noble gases. As the number of electrons in the molecule 
increases, so do the van der Waals’ forces. This explains why there is an increase in boiling 
point as we go down the group of halogens, and down the group of …(16)… gases.
So to recap, an intermolecular force is simply an attractive force between neighboring 
molecules. The three common intermolecular forces are (1) permanent dipole-dipole forces; 
(2) hydrogen bond; and (3) van der Waals’ forces. 

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