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4.5.2 Classification of Substances

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Classification of Substances

1. Types of substances:


 
2. The physical properties of substances depend on
 (a)  types of particles they contain,
   (b)  arrangement of the particles,
   (c)  forces of attraction between the particles.


Substances made of atoms (or Atomic substances)
1.   Atomic substances are substances that consist of only atoms.
2.   The atoms in atomic substances are arranged closely together in a fixed pattern and only can vibrate in their fixed positions.
3.   Atomic substances have high melting and boiling points owing to strong metallic bond.
4.   They are able to conduct electricity owing to presence of free electrons.
5.   All metals are atomic substances such as iron, aluminium and calcium.


Substances made of molecules (or Molecular substances)
1.   Molecular substances are made up of molecules which have two or more atoms of the same type or different types.
2.   For example, two oxygen atoms combine to form one oxygen molecule. On the other hand, one nitrogen atom combines with three hydrogen atoms to form one ammonia molecule.
3.   Examples of other molecular substances are hydrogen, nitrogen, carbon dioxide, sulphur dioxide, chlorine gas and iodine.
4.   Molecules are held together by weak intermolecular force (or van der Waals forces) and have low melting and boiling points.


5.   Molecules are made up of non-metal atoms which are poor conductors of electricity because there are no free electrons or ions in any state to carry electric charge.


Substances made of ions (or Ionic substances)
1.   Substances that made up of ions are called the ionic compounds.
2.   They are compounds of metal bonded with non-metal.
3.   Examples of ionic compounds are sodium chloride, copper (II) sulphate, sodium hydroxide and lead (II) oxide.
4.   Positive and negative ions are held together by strong ionic bonds. This strong bonding force makes ionic compounds has high melting and boiling points.
 

Arrangement of ions in a compound

5.   All ionic compounds are crystalline solids at room temperature.
6.   The solid crystals do not conduct electricity because the ions are not free to move to carry an electric current.
7.   However, if the ionic compound is melted or dissolved in water, the liquid will now conduct electricity, as the ion particles are now free.

5.4.2 Meiosis (Structured Question 1 & 2)

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Question 1:
Diagram I shows the different stages in a cell division.


(a)(i) Name the type of cell division.


(a)(ii) Arrange the stages of the cell division in the correct sequence.

(b)(i) Explain the chromosomal behaviour in stage C.

(b)(ii) State one importance of the chromosomal behaviour in (b)(i).

(c) Diagram II shows the involvement of cells produced by this type of cell division in the formation of zygote.


Explain how zygote is formed.


(d) Diagram III shows the karyotype of an offspring produced.


(i) State the number of chromosomes in the offspring.

(ii) Name the genetic disease suffered by the offspring.

(iii) Give one reason for the answer in (d)(ii).

(iv) Explain how radioactive rays can cause this genetic disease.


Answer:
(a)(i)
Meiosis I

(a)(ii)

(b)(i)
The chromosomes condense, thicken and become clear.
Homologous chromosome exchange the genetic material in a process of crossing over.

(b)(ii)
Increases genetic diversity/ causes variation.


(c)
When the nucleus of a sperm (haploid) fuses with the nucleus of an ovum (haploid) during fertilization, a zygote (diploid) is formed.

(d)(i)
45/ 44 + X

(d)(ii)
Turner’s syndrome

(d)(iii)
The absence of one X chromosome which is a sex chromosome

(d)(iv)
Radioactive radiation can cause mutation of the chromosomes, as a result of which only one X chromosome is present.


4.5 Properties of Substances Based on their Particle Content

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4.5 Properties of Substances Based on their Particle Content

1.   Matter is anything that occupies space and has mass.
2.   Matter can be divided into elements and compounds.




4.5.1 Atoms, Molecules and Ions
1.   Substances are made of tiny particles called atoms, molecules and ions.
2.   Atoms are the tiniest particles in an element.
3.   A molecule consists of two or more atoms of the same type or of different types that are chemically combined together.
4.   Ions are particles which carry positive or negative charges.




5.4.1 Mitosis (Structured Question 1 & 2)

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Question 1:
Figure I shows cells R and S undergoing cell division.


(a)(i) Name the structures labelled K and M.

(a)(ii) State the phase of division of cells R and S.


(b) Cell R undergoes three consecutive divisions.

(c)(i) Cell S undergoes the first nuclear division and produces two cells.
Complete the diagram to show the chromosomes in one of the cells produced.

(c)(ii) Name one organ where cell S is found.

(c)(iii) The number of chromosomes I a somatic cell of a fly is 12.
State the number of chromosomes in a daughter cell produced at the end of the type of cell division as shown by cell S.


(d) Cancer is a disease which causes uncontrolled growth of tissues.
Radiotherapy is a method to treat cancer by using radiation.
Explain how this treatment stops the growth of cancer cells.

(e) An oil palm planter wants to produce a large number of oil palms in a short time.
State the best technique to be used by the planter and one problem to be considered in using the technique.



Answer:
(a)(i)
K: Chromatid
M: Spindle fibre

(a)(ii)
Cell R: Metaphase
Cell S: Metaphase I

(b)
8 daughter cells

(c)(i)



(c)(ii)
1. Testis
2. Ovary

(c)(iii)
6 chromosomes

(d)
Radioactive rays destroy the cells, so the rate of mitosis is controlled.

(e)
- Cloning / culture tissue
- All the clones are easily attacked by diseases because all the clones have the same resistance towards diseases.


4.4 Classification of Elements in the Period Table

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4.4 Classification of Elements in the Period Table







4.4.1 The classification of Elements

1. In modern periodic table, the elements are arranged in ascending order of proton number.



Group
1. The vertical columns of the periodic table is called group.

2. There are 18 groups in the periodic table.

3. Elements in the same group have similar chemical properties.
Example:
Elements in Group 1 react violently with water to produce metal hydroxide, hydrogen and heat.

4. Elements in groups 1 and 2 are very reactive metals (except hydrogen).

5. Elements between groups 2 and 13 are called the transition elements.

6. Transition elements are metallic elements. Most of them are hard and shiny. All transition elements are good conductors of electricity.

7. The elements in group 17 are non-metals called halogens.

8. Group 18 consists of noble (inert) gases, which are inactive gases.


Period
1. The horizontal rows is called the period.

2. There are 7 periods in period table.

3. The first period has 2 elements only.

4. The second and third period consist of 8 elements, are called the short period.

5. The forth and the fifth period consist of 18 elements, are called the long period.

6. The sixth and the seventh period have 32 elements.

7. The chemical and physical properties of the elements are gradually changed when crossing periods.


4.4.2 Metals, Semi-metals and Non-metals
1. The elements in the Periodic Table are divided into metals, semi-metals and non-metals.

2. Most elements in group 1, 2, 13 and transition elements are metals.

3. Most non-metal elements are located in groups 16, 17 and 18.

4. Seven elements between metals and non-metals are semi-metals. Semi-metals possess certain properties of metals and non-metals.

5. When moving across a period from left to right, the properties of metal change gradually to those of semi-metal and finally non-metal.  

6. The metals become increasingly active as they move down the table.


4.4.3 Importance of the Periodic Table
1. The periodic table enables us to study the elements in an orderly and systematic way.

2. It helps us to know the properties of elements that fall into a particular group.

3. It enables us to predict the properties, reactions and uses of the elements.