PARTICULATE NATURE OF MATTER-I

 

Week:                                                                                     Date:                                                    

Period:                                     Duration:                                             Average age of learners: 15 YEARS

Subject: CHEMISTRY                                                                           Class: SS ONE

Topic:             PARTICULATE NATURE OF MATTER - I

Sub topic:  The concept of atom, molecules and ion

Reference materials:

(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA

(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO

(3) INTERNET

Instructional materials:

Entry behavior: The students have been familiar with some common element.

Behavioural objective: At the end of the lesson the students should be able to:

Content

MATTER

Matter is anything that has weight (mass) and occupies space. There are three building blocks of matter which are as follow: i. Atom ii. Molecule iii. Ions.

ATOMS

An atom is the smallest particle of an element which can take part in a chemical reaction. An atom can also be said to be the smallest particle of an element that can ever exist and still possess the chemical properties of that element.

 

MOLECULES

Most atoms cannot exist alone. They generally bond with other atoms to form molecules. Therefore, atoms can be made up of atoms of either the same elements or different elements.

     The number of atoms in each element is called Atomicity of the element.

Most gaseous elements such as chlorine, hydrogen, oxygen, nitrogen etc., are DIATOMIC (Molecules with one atom)

Some elements may be MONO ATOMIC (Molecules with one atom); for example, noble gases (Argon (Ar), helium (He), Neon (Ne))

TRIATOMIC molecules (Molecules with three atom), for example; ozone (O₃).

POLYATOMIC molecules (Molecules with three atom), for example; phosphorous, Sulphur.

Atomicity of some molecular elements

Element	Formulae	Atomicity
Neon	Ne	1
Argon	Ar	1
Helium	He	1
Hydrogen	H2	2
Nitrogen	N2	2
Oxygen	O2	2
Chlorine	Cl2	2
Ozone	O3	3
Phosphorous	P4	4
Sulphur	S8	8

 

Note: A molecule can be defined as the smallest particle of a substance that can normally exist alone and still retain the chemical properties of that substance be it an element or a compound.

IONS

An ion is formed when an element loses or gains electrons. It carries a positive charge when electrons are lost and negative charge when electrons are gained.

     However, an atomic substance is said to be electrically neutral when it has the same number of positive and negative ions. That is, it has no charge.

Note: An ion can also be defined as any atom or group of atoms which possesses an electric charge. Examples are, NH₄⁺, Ca²⁺ ,Cu²⁺ ,O^2-, SO₄^2-, SO₃^2- , OH^- , Na⁺  etc.

Dalton's Atomic Theory

Democritus first suggested the existence of the atom but it took almost two millennia before the atom was placed on a solid foothold as a fundamental chemical object by John Dalton (1766-1844). Although two centuries old, Dalton's atomic theory remains valid in modern chemical thought. Dalton based his theory on the law of conservation of mass and the law of constant composition.

Dalton's Atomic Theory 1) All matter is made of atoms. Atoms are indivisible and indestructible. 2) All atoms of a given element are identical in mass and properties 3) Compounds are formed by a combination of two or more different kinds of atoms. 4) A chemical reaction is a rearrangement of atoms.

Modern atomic theory is, of course, a little more involved than Dalton's theory but the essence of Dalton's theory remains valid. Today we know that atoms can be destroyed via nuclear reactions but not by chemical reactions. Also, there are different kinds of atoms (differing by their masses) within an element that are known as "isotopes", but isotopes of an element have the same chemical properties.

Many heretofore unexplained chemical phenomena were quickly explained by Dalton with his theory. Dalton's theory quickly became the theoretical foundation in chemistry.

  Presentation of teacher activity:

i.  The teacher defines element and list the first- thirty elements.

ii. The teacher defines a compound with relevant examples.

iii. The teacher explains mixture and their types

Students’ activities:

i. The students chorus the definition of element

ii. The students mention example of compound

iii. The students differentiate between the types of mixture

Evaluation: The teacher evaluates the lessons by asking the following questions:-

(i)                   define element

(ii)                 what are the constituents of calcium hydroxide and potassium iodide

(iii)                Briefly explain a mixture