CHEMISTRY-Chapter 2 Structure of the Atom

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CHEMISTRY

The Structure Of The Atom >> Matter_Note 1

The Structure Of The Atom

Matter

Matter is anything that occupies space and has mass. Any substance that exists in solid, liquid

or gaseous is a matter. Matter is made up of tiny and discrete particles. These particles may be

atoms, ions or molecules. Then,

(a) An atom is a smallest neutral particle of an element that can take part in chemical reaction.

Examples: zinc atom, Zn, oxygen atom, O, and hydrogen atom, H..

(b) A molecule is a neutral particle made up of either atoms of the same element or atom of

different elements. Examples: oxygen molecule, O2 , and water, H2 O(c) An ion is a charged particle which consists of either atom or atoms from different elements.

Examples Sodium ion is a positive charge ion, Na+ and chloride ion is negative charge ion, Cl-.

Matter can either be existing as element or compound. An element consists of only one type of

atom and the particles can be either atoms or molecules. Then a compound is usually made up of

two or more elements which are chemically bonded together.

Kinetic theory of matter said, particles in matter are in motion. They are moving randomly and

collide with one another. For an example, see a Figure 1 and discuss with your friend about the

moving of the particles in tornado.

These experiments are carried out to investigate the diffusion of solid, liquid and gas.



Apparatus: Gas jar and cover, dropper, test tubes, retort stand and clamp, rubber stopper

Materials : potassium manganate (VII) crystal, liquid bromine, hot liquid gel.

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a) Diffusion in a solid

Procedure:

(i) A test tube is filled with hot liquid gel and left to harden.

(ii) A small crystal of potassium manganate (VII) is put on top of the gel.

(iii) The test tube is stopped and clamped upside down as shown in figure 2.

(iv) The apparatus is left to stand for two days.

(v) The observation on the colour of the gel is recorded.

b) Diffusion in a liquid

Procedure

(i) A test tube is filled three quarter full with water and placed in a test tube rack.

(ii) A small volume of potassium manganate (VII) solution is sucked into a dropper.



(iii) The tip of the dropper is carefully lowered into the water until it reaches the bottom of the

test tube as shown in Figure 3.

(iv) One dropped of potassium manganate (VII) solution is squeezed into the water.

(v) The test tube is allowed to stand for a few hours.

(vi) The observation on the colour of the water is recorded

c) Diffusion in a gas

Procedure

(i) A few drops of liquid bromine is placed in a gas jar. The gas jar is covered and left for a few

minutes for the liquid bromine to evaporate.

(ii) A gas jar full of air is inserted on top of the gas jar of bromine gas as shown in figure 4.

(iii) The cover is moved and left for a few minutes.

(iv) The observation on the colour of both gas jars are recorded

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Questions:



1. Record each observations of the activity (a), (b) and (c) in a table.

2. Write the conclusion for the diffusion of particles in solid, liquid and gas.

3. If bromine in section (c) replace by chlorine which is more lighter than bromine, what will

happen in the gas jars.

Experiment 2 is carried out to determine the melting point of naphathalene.

The melting point or freezing point is the temperature at which a substance changes between the

solid and liquid states. The melting point and freezing point of naphthalene, C10H8 is about 78oC.

CHEMISTRY

The Structure Of The Atom >> The Atomic Structure_Note 1

The Atomic Structure

Development of atomic models





According to the modern atomic model,

(a) protons and neutrons are located in the nucleus

(b) the nucleus is very small compare to size of the atom

(c) the electrons are orbiting outside the nucleus in their shells

(d) the mass of the atom is the sum of protons and neutrons for each atom



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Scientists have proven that they are very tiny particles in atom which called subatomic particles.

Table 1 shows the mass and elative charge of subatomic particles:

From our previous lesson, arrangement of properties of subatomic particles as shown in figure 1

below



The nucleus of an atom attract the electrons by electonic force because of the differences of

charge between protons and electrons in an atom. From figure 1, electrons are arranged in the

shells around the nucleus in theirs shells. Each shells has a different level of energy and occupied

with certain amount of electrons. For secondary level, arrangement of electrons in each shell as

shown in figure 2 :

The nearest shell is numbered by 1, second shell is numbered by 2, third shell is numbered by 3

and forth shell is numbered by 4. The maximum number of electrons can held in each shells isshown in figure 2.

You must remember that, protons and neutrons are found in the nucleus which sum of protons

and neutrons will be the mass of an atom. The number of electrons are same with the number of

protons in an atom. So an atom is electrically neutral.


Isotopes

Some atoms in periodic table have same number of protons but different number of nucleus.

Therefore, these atoms are called isotopes . Table 2 shown, isotopes of oxygen and chlorine .



Although oxygen and chlorine are isotopes, number of electrons are still same .

There are two type of isotopes, namely non-radioactive isotopes and radioactive isotopes.

Radioactive Isotopes are very useful in our daily lives such as in field of

�Medicine

(i) gamma rays of cobalt-6- are used for the treatment of cancer

(ii) plutonium-238 in a nuclear battery is used to produce small electric shocks to treat patients

with heart disease.

�Agriculture

Carbon -14 is added in carbon dioxide to study photosynthesis in plants and to determine the age

of ancient artifacts.

�Industry

Sodium-24 are used to detect leaks in pipes that transport water, gas or oil underground

�Food industry Cobalt-60 are used to kill bacteria in food to make fresh vegetables and fruits.

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CHEMISTRY-Chapter 2 Structure of the Atom