Structure of Atom

Subject :  Basic Science and Technology

Class : Jss3 Year 9

Topic : Simple Atomic Structure

Behavioral  Objectives :

At the end of the lesson , pupils should be able to

• Define the following terms and give two examples of each (a)mixtures (b) compound and (c) molecules
• mention two things each can be used for
• state the difference among elements, compounds and mixtures  

: SIMPLE ATOMIC MODEL

Ernest Rutherford in 1909 proposed a model of the atom. His model showed a small dense, positively charged nucleus surrounded by relatively empty space and electrons continuously orbiting the nucleus at a great distance from it. However in the light of further experimental results, other models of the atom have been proposed.

The electrons occupy different orbits or shells called K,L,M,N, shells or 1,2,3,4, shells round the nucleus. These shells may also have sub shells designated s, p d, subshells.

Examples are;

(i)   Hydrogen

Electron on K shell

Nucleus

(ii) Sodium

M shell

L shell

K shell

STRUCTURE OF MATTER

Structure of Matter

Modern physics has revealed successively deeper layers of structure in ordinary matter. Matter is composed, on a tiny scale, of particles called atoms. Atoms are in turn made up of minuscule nuclei surrounded by a cloud of particles called electrons. Nuclei are composed of particles called protons and neutrons, which are themselves made up of even smaller particles called quarks. Quarks are believed to be fundamental, meaning that they cannot be broken up into smaller particle.

PROPERTIES OF ATOMS

Atoms have several properties that help distinguish one type of atom from another and determine how atoms change under certain conditions. These properties include;

• The Atomic number: The number of protons in the nucleus of an atom is called its atomic number (Z). All atoms of the same element have the same number of protons and so have the same atomic number. Atoms are normally electrically neutral so the atomic number also shows how many electrons an atom has. However, an atom may lose or gain an electron to become a charged particle called an When an atom loses an electron it forms a positively charged ion called a cation. When an atom gains an electron it forms a negatively charged ion called an anion. The number of electrons thus determines many of the chemical and physical properties of an atom.

• The Mass number: The sum of the protons and neutrons in the nucleus of an atom is called the mass number of the atom (A). The number of neutrons is denoted by N.

The relationship between the number of neutrons and protons is given by; A=Z – N

• The Atomic Mass and Weight: Scientists use a device called a mass spectrometer to measure atomic mass. The mass of an atom is measured in terms of a unit called theatomic mass unit (amu). An amu is defined as exactly 1/12 the mass of an atom of carbon with six protons and six electrons.

An element’s atomic weight represents the mass of one mole of its atoms. A mole is the mass of a very large number of atoms. A mole of atoms of any element contains 6.02 × 10²³ atoms. This is also called the molar mass.

• Isotopes: Atoms of the same element that differ in mass number (A) are called isotopes. They have the same atomic number (Z). These elements have the same number of protons in their nucleus but different numbers of neutrons. For example, hydrogen has three isotopes ¹H; ²H; ³H called Protium, Deuterium and Tritium respectively.

HYDROGEN ISOTOPES

EVALUATION

1. Draw a simple atomic model of Helium atom with two electrons, two protons and two neutrons.
2. Briefly describe the three types of hydrogen atoms that exist.
3. Write the (a) mass number (b) atomic number of Sodium atom.

Sub-Topic 3:Concept of Elements, Molecules, Compounds and Mixtures

ELEMENT: A substance that is made up of only one type of atoms is called an element. An element cannot be broken down into anything else. Examples are magnesium, copper, zinc,gold, iron, oxygen, carbon, chlorine, etc.

MOLECULE: The smallest unit of a substance which can exist on its own and retain the properties of the substance is called a molecule. A molecule may be made up of one atom only e.g. Argon (Ar) or a combination of atoms e.g. Oxygen (O₂).

COMPOUND: A substance formed by the chemical combination of the atoms of different elements is a compound. Examples are Sodium chloride (salt), water, kaolin, carbon (iv), oxide, sand,etc.

MIXTURE: A substance formed when elements or compounds are mixed without any chemical reaction occurring is called a mixture. Examples are crude oil, soil, cup of tea, air, palm oil, solution of salt and water, etc. The components of a mixture can be separated by physical means like evaporation, magnetization, filtration, Sublimation, etc.

PROPERTIES OF ELEMENTS, COMPOUNDS AND MIXTURES

1. ELEMENTS:

(a) Chemical Properties:

• Some elements are very reactive e.g. Sodium, Potassium, Chlorine, Oxygen, etc. Sodium metal readily gets ignited on exposure to air.
• Some elements are moderately reactive e.g. when iron is exposed to moist air it gradually begins to rust.
• Some elements are virtually unreactive e.g. Gold does not rust when exposed to moisture.

(b) Physical Properties

(i)        Some elements have light density e.g. Hydrogen gas while some are heavy e.g.

Gold, Lead, etc.

(ii)     Some elements are colourless e.g. Oxygen, Hydrogen and Nitrogen while some are

coloured e.g. Chlorine, Bromine, etc.

• Solid, non-metallic elements are brittle and have a dull surface e.g. Phosphorus and Sulphur while the metallic elements are malleable and have a shiny surface e.g. Iron and Aluminium
• All metals exist as solids at room temperature except Mercury which is a liquid.

2. COMPOUNDS:

 (a) Physical Properties:

• Most compounds formed from the chemical combination of metals and non-metals are soluble in water but not in organic solvents like kerosene.
• Compounds formed from the chemical combination of non-metals are soluble in organic solvents like kerosene and petrol.
• Compounds have definite melting and boiling points.

(b) Chemical Properties

(i)  Some chemicals react chemically with acids to form a new compound e.g. sodium

hydroxide and hydrochloric acid react chemically to form sodium chloride and

water.

(ii)  Some compounds decompose on heating e.g. calcium trioxocarbonate (iv) on

heating produces calcium oxide and carbon (iv) oxide.

3. MIXTURES: Physical Properties:

• Mixtures can be separated by physical means.
• Mixtures do not have definite boiling or melting points.
• The colour of individual constituents is visible.

USES OF SOME ELEMENTS, COMPOUNDS AND MIXTURES

USES OF ELEMENTS

(a) Gold is used in making jewelry and coins. It is also used in art work and dentistry. Radioisotopes of gold are used in biological research and in treatment of cancer.

(b) Iron is used for production of galvanized sheet metal and electromagnets. Iron compounds are used for medicinal purposes in the treatment of anemia and also in tonics.

USES OF COMPOUNDS

(a) Kaolin is used in the manufacture of fine porcelain and china ware; pottery, stoneware and bricks; as a filler for pigments and manufacture of       paper.

(b) Salt is used as a seasoning; as preservative for meats; in dyeing and in manufacture of soap and glass. Table salt is combined with small quantities of iodide to prevent occurrence of goiter. Industrially salt is a source of chlorine and sodium. Chlorine is used in manufacture of hydrochloric acid, chloroform and bleaching powder. Sodium is used for sodium carbonate, baking soda and sodium hydroxide.

USES OF MIXTURES

(a) Crude oil is used as fuel (petrol, kerosene, diesel, gas, etc.) and raw material in the chemical industry. Derivatives are used in manufacture of medicine, fertilizers, plastics, paints, building materials and for generating electricity.

(b) Coal is used as fuel. It is used by electric power plants to produce electricity. Industrially it can be converted to coke and mixed with iron ore and limestone to produce iron. The coal gases given off during the process of coke formation are used to manufacture solvents, fertilizers, medicine, pesticides, etc.

EVALUATION

1. Define the following terms and give two examples of each (a) element (b) molecule (c) compound (d) mixture
2. Mention two things each example can be used for.
3. Enumerate three differences between elements, compounds and mixtures

WEEKEND ASSIGNMENT

1. Complete the missing information below

2. Air is a mixture of gases, mention three of the gases and state two uses of each
3. Collect twelve (12) materials from your environment and classify them into elements, compounds and mixtures.

READING ASSIGNMENT

Functional Basic Science for JJS Book 3; by Onyirioha, C. U et al. (pgs 70-80)