PARTICULATE NATURE OF MATTER

 

 

FIRST TERM E-LEARNING NOTES

SUBJECT: CHEMISTRY

CLASS: SS1

WEEK 2

Topic: PARTICULATE NATURE OF MATTER

CONTENTS:

(1) Physical and chemical changes

(2) Elements and their symbols.

(3) Atoms, molecules, atomicity

(4) Dalton’s atomic theory

PERIOD 1: PHYSICAL AND CHEMICAL CHANGES

PHYSICAL CHANGES:

DEFINITION: A Physical change is one which is easily reversed and in which no new substances are formed.

Examples:

i. Melting of solids to liquids.

ii. Freezing of liquids to solids.

iii. Vaporization of liquids to gases.

iv. Liquefaction of gases to liquids.

v. Sublimation of solids to vapour.

CHEMICAL CHANGE:

DEFINITION: A chemical change is one which is not easily reversed andin which a new substance is formed.

Examples:

i. Burning of substances.

ii. Dissolution of metals and limestone in acids.

iii. Chemical decomposition – like digestion of food.

iv. Rusting of iron.

v. Charring of sugar.

vi. Dissolution of metals in acids.

DIFFERENCES BETWEEN PHYSICAL AND CHEMICAL CHANGE

PHYSICAL CHANGE CHEMICAL CHANGE

  1. Easily reversible Not easily reversible
  2. No new substance is formed New substance is formed
  3. No change is mass. There is a noticeable change in mass.
  4. Not accompanied by heat usually accompanied by heat change.

Change.

EVALUATION:

  1. Mention three familiar process/changes which you know to be: (a) Physical changes (b) chemical changes.
  2. List three differences between physical change and chemical change.
  3. Classify each of the following as physical change or chemical change.

(a) Boiling of egg (b) Burning of kerosene (c) Melting of wax (d) Rusting of iron (e) Digestion of glucose (f) Dissolving iron in an acid.

  1. State with a reason in each case whether each of the following is physical or chemical change.
  1. Dissolving common salt in water.
  2. Burning of petrol.
  3. Digestion of glucose.

PERIOD 2: ELEMENTS AND THEIR SYMBOLS

An element is a substance that cannot be broken into simpler substances by any chemical methods. Examples of elements include: Iron, tin,

There are about 118 known elements of which 92 araluminum etc.e naturally exiting elements and the rest are artificially made.

Symbols are modern ways of representing atoms of elements by using abbreviations. The modern symbols were developed by Berzelius in 1814.

First, He used the first letter in the name of the element.

Examples

ELEMENT SYMBOL

Hydrogen H

Boron B

Carbon C

Nitrogen N

Oxygen O

Fluorine F

Phosphorus P

Sulphur S[mediator_tech]

Iodine I

The second principle uses the first two letters.

Examples:

ELEMENTS SYMBOL

Helium He

Lithium Li

Beryllium Be

Neon Ne

Aluminum Al

Silicon Si

Argon Ar

Calcium Ca

Bromine Br

Barium Ba

The third principle is when the first letter and another letter in the name are used.

Example:

ELEMENTS SYMBOL

Magnesium Mg

Chlorine Cl

Chromium Cr

Manganese Mn

Zinc Zn

The fourth principle is the elements that derived symbols from their Latin names.

Example:

ELEMENT LATIN NAME SYMBOL

Sodium Natrium Na

Potassium Kalium K

Iron Ferrum Fe

Copper Cuprum Cu

Silver Argentum Ag

Tin Stannum Sn

Gold Aurum Au

Mercury Hydrargyrum Hg

Lead Plumbum Pb

PERIOD 3: ATOMS, MOLECULES AND ATOMICITY

ATOMS

DEFINITION: An atom is the smallest particle of an element which can take part in a chemical reaction.

STRUCTURE AND CONSITITUENTS OF AN ATOM

An atom is made up of the three sub-particles known as protons, neutrons and electrons as shown in the diagram below. Their characteristics are also summarized in the table below:

Electron

Nucleus

CHARACTERISTICS OF THE SUB-PARTICLES

SUB-PARTICLE LOCATION RELATIVE CHARGE RELATIVE MASS SYMBOL
Proton Nucleus + 1 p
Electron Outside nucleus _ 0.005 e
Neutron Nucleus Zero 1 n

MOLECULES

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

Some molecules can exist independently as single atoms e.g. He, Ne, Ar, Xe etc. Some molecules may be made up of atoms of the same element e.g. a molecule of hydrogen is H2, that of chlorine is Cl2, Oxygen is O2, phosphorus is P4, Sulphur is S8. Some molecules may be made up of different elements e.g. a molecule of water is H2O, Methane is CH4, ammonia is NH3, carbon (iv) oxide is CO2 etc.

ATOMICITY: Atomicity is the number of atoms in each molecule of an element.

Atomicity of some molecules

Element Formula of molecule Atomicity
Hydrogen H2 2
Oxygen O2 2
Ozone O3 3
Phosphorus P4 4
Sulphur S8 8
Chlorine Cl2 2
Neon Ne 1
Argon Ar 1
Tetraoxosulphate(vi) acid H2SO4 7
Amonium tetraoxosulphate(vi) (NH4)2SO4 15

PERIOD 4: DALTONS ATOMIC THEORY

In 1808 John Dalton proposed the following Atomic theory.

  1. All elements are made up of small indivisible particles called atoms.
  2. Atoms can neither be created or destroyed
  3. Atoms of the same element are alike in every aspect, and differ from atoms of all other elements.
  4. When atoms combine with other atoms, they do so in simple ratios.
  5. All chemical changes result from the combination or the separation of atoms.

MODIFICATIONS OF DALTON’S ATOMIC THEORY

The following are the modifications to Dalton’s atomic theory.

  1. All matter is made up of small particles, protons, neutrons and electrons.
  2. An atom can be destroyed and created; when radioactive atoms disintegrate with the emission of particles, new atoms are produced.
  3. The atoms of the same elements are not all alike, but may have different masses as proved by the phenomenon of isotopy.
  4. In large organic molecules, such as proteins, fats and starch, the combining ratio are in large whole number.

EVALUATION:

  1. What are the three fundamental units of all matter? Give their relative masses and charges.
  2. Describe their relative positions to one another in an atom.
  3. Name the two main part of an atom?
  4. Mention the three subatomic particles in an atom.
  5. Which particles are found in each part of the atom?
  6. List three sub atomic particles with their corresponding charges.
  7. State four Dalton’s atomic theory with their modifications.

GENERAL EVALUATION

OBJECTIVE TEST:

  1. The simplest unit of Matter that retains its properties is called. (a) an atom (b) an element (c) an hydroxide (c) a molecule
  2. Of the basic particles that make up an atom, the one with the smallest mass is? (a) a proton (b) a neutron (c) an x- particle (d) an electron
  3. The following are physical changes except: (a) melting of candle wax (b) Dissolving common salt in water (c) Freezing of water (d) Rotting of leaves.
  4. Which of the following is not a molecule of the same element. (a) O2 (b) P4 (c) S8 (d)CO2
  5. The atomicity of O3 is (a) 1 (b) 2 (c) 3 (d )4

ESSAY QUESTIONS

  1. Write four examples in each case of (a) Physical change (b) Chemical change[mediator_tech]
  2. Define the following giving two examples in each case. (a) Atom (b) Ion
  3. Write the symbols for proton, electron and neutrons.
  4. Define atomicity giving two examples.
  5. Write four Dalton’s atomic theory.

WEEKEND ASSIGNMENT

Write the electronic configuration of the first twenty element using the concept of K,L,M,N and the sub-energy atomic level configuration i.e. s,p,d,f.

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