Ace Your Class 9 Board Exams & Entry Tests with Fundamentals of Chemistry Notes
"Discover the Fundamentals of Chemistry with ease with our comprehensive notes for Class/Grade 9 students. In this article, we cover key concepts such as basic definitions, the brief history of chemistry, and the role of Muslim scientists in shaping the discipline. We also delve into important topics like the atomic number, atomic mass, mole, Avogadro's number, molecular mass, and formula mass, and provide simple chemical calculations to help you master these concepts. These notes are essential for students preparing for exams such as Class 9 BISE, Federal Board, NMDCAT, NEET, ETEA, Cadet Colleges Entry Tests, and other competitive exams. Boost your understanding and increase your chances of success with these essential Chemistry Notes."
For Long and Comprehensive Answers on this chapter Click Here
 |
| Chemistry Notes for Grade IX BISE & Board exams From the Notes Library of H.E.S (Health, Education, and Skills) |
Define the following
terms |
I. Science
|
The knowledge
obtained through observations and experiments is called Science. |
ii. Chemistry
|
The branch of science that deals with the study of
|
iii. Matter
|
Anything which occupies space and has mass is called matter. |
Matter exists in four states i.e. solid, liquid, gas, and plasma.
iv. Pure Substance
|
Anything that is obtained from different sources but has the same composition and properties is called a pure substance or simply a substance. |
For example, water can be obtained from oceans, rivers, wells, seas, etc. but it will have the same composition and same properties from wherever it is obtained.
v. Element
|
A pure substance that can’t be broken down into simpler substances by ordinary chemical or physical means is called an Element. |
For example, Hydrogen, Oxygen, Iron, Copper, etc. are some examples of elements.
vi. Compound
|
A pure substance that can be only formed as well as broken down into simpler substances by chemical means only is called a Compound. |
For example, Sodium Chloride (NaCl) is a compound, because it can be formed by an Ionic bond and can be broken down into Sodium (Na) and Chlorine (Cl) by a chemical mean called Electrolysis.
vii. Mixture
|
Anything that can be formed as well as can be separated by physical means only is called a Mixture. |
For example, Sugar and Water when mixed by stirring form a mixture, and similarly they can be separated by heating which is a physical means.
Briefly state the history of Chemistry |
History of Chemistry
The history of Chemistry can be divided into the following four periods
- Egyptian’s period
- Greek’s period
- Muslim’s period
- Roman’s period
Muslims for the first time presented Chemistry as practical knowledge; for this purpose, they invented much chemical equipment
as well as chemical procedures. The
period from 600 to 1600 AD is known as the period of Muslim chemists or more
precisely the period of Alchemists
in the history of chemistry.
The knowledge of Alchemists and the techniques they used gradually spread to Europe and the term Alchemy used for the knowledge of Alchemists changed into a purely English Word Chemistry.
What were the aims and achievements of Alchemists? |
Aims and Achievements of Alchemists
The period from 600 to 1600 AD is the period of Muslim scientists which is generally known as the period of Alchemists. They laid down the foundation of sciences like Physics, Chemistry, Biology, Mathematics, Astronomy, Medicine even music.
The primary aims of the Al-Chemists were
- To look for ways to change the base metals into Gold, however, they didn’t succeed in their aim.
- To find out methods to prolong life.
- To find physical evidence to support religious and philosophical beliefs.
Alchemists made the following achievements
1. Discovered elements: Al-Chemists discovered Arsenic (As), Antimony (Sb), and Bismuth (Bi).
2. Laboratory equipment: Al-Chemists invented many laboratory types of equipment like beakers, crucibles, retorts, furnaces, etc.
3. Laboratory procedures: Al-Chemists also invented many laboratory procedures like sublimation, fermentation, filtration, calcination, etc.
4. Preparations: Al-Chemists prepared many Acids, Alkalies (Bases), medicines, and Alcohol.
Define and give examples of |
I. Atomic Number (Z)
|
In an atom, the total number of protons present in the nucleus is called the atomic number. |
The atomic number is represented by the letter Z. For example, In Sodium, there are 11 electrons and 11 protons so the atomic number of Sodium is 11. Similarly, the atomic number of Hydrogen is 1 which shows that there is 1 electron and 1 proton in the Hydrogen atom.
It has been found that the atoms of one element differ from those of other elements by the number of protons in their nuclei. No two elements have the same number of protons. An atom is a neutral particle because in an atom the number of protons is always equal to the number of electrons. The number of neutrons in an atom cannot be used to characterize the atom. Therefore, elements are arranged in the modern periodic table on the basis of an increasing number of protons.
II. Mass Number
In an atom, the sum (Total) of neutrons and protons is called the Mass Number. |
Atomic Mass is represented by the letter A. For example, the atomic mass of Carbon is 12. Symbolically the information about the atom can be written as
AXZ
Where A is the atomic mass and Z is the atomic number of an element.
For example, Carbon has an atomic mass of 12 and atomic number 6 so can be written in the above form as
12C6
The atomic number, mass number, and sub-atomic particles of some atoms are given in the below table
|
Elements |
No of
electrons |
No of
Protons |
No of
Neutrons= (A-Z) |
| 107Ag47 | 47 |
47 |
107 – 47 = 60 |
|
23Na11 |
11 |
11 |
23 – 11 = 12 |
|
56Fe26 |
26 |
26 |
56 – 26 = 30 |
|
40Ar20 |
20 |
20 |
40 – 20 = 20 |
|
16O8 |
8 |
8 |
16 – 8 = 8 |
|
24Mg12 |
12 |
12 |
24 – 12 = 12 |
|
31P15 |
15 |
15 |
31 – 15 = 16 |
|
238U92 |
92 |
92 |
238 – 92 = 146 |
Remember that: Atomic Mass and Mass number are not the same.
- Atomic mass is the weighted average of all the isotopes of an element and is usually expressed in atomic mass units (amu).
- Mass number, on the other hand, is the sum of the number of protons and neutrons in the nucleus of an atom and is a whole number.
Define the Chemical formula. Also, describe types of Chemical formulas. |
Chemical Formula
The symbolic representation of a molecule of a compound is called the Chemical formula. |
For example, the formula of salt (NaCl) is the combination of the symbols of Na and Cl elements.
Types of Chemical Formula
Following are some types of Chemical formulas.
1. Empirical Formula
The simplest formula that gives the smallest whole-number ratio of the atoms or ions in a compound is called the Empirical formula. |
Explanation
Take the example of Benzene C6H6
The actual ratio between Carbon and Hydrogen in Benzene is 6:6
By simplifying the ratio between Carbon and Hydrogen we get 1:1
So the empirical formula of Benzene will be C1H1 or simply CH.
Similarly, Glucose has the actual formula as C6H12O6 in which there is 6:12:6 among the Carbon, Hydrogen, and Oxygen but after simplifying the ratio we have the empirical formula of Glucose as C1H2O1 or CH2O.
An empirical formula always gives the correct ratio among the elements in a compound but it may not be the actual formula.
2. Molecular formula
That type of chemical formula that shows the actual number rather than the simplest ratio of constituent atoms per molecule of the compound is called the Molecular formula. |
Explanation
The molecular formula is the actual formula of a compound because it shows the actual number of atoms in the formula of a compound. For example, the molecular formula of water and Benzene is H2O and C6H6 respectively, which are their actual formulas also.
Relation between Empirical and Molecular formula
The relation between the Empirical and Molecular formulas is given as
Molecular mass = n x Empirical formula mass
And n = Molecular mass/Empirical formula mass
|
Sr No |
Compound |
Empirical Formula |
Molecular Formula |
Compound Type |
|
1 |
Acetylene |
CH |
C2H2 |
Molecule |
|
2 |
Benzene |
CH |
C6H6 |
Molecule |
|
3 |
Acetic
Acid |
CH2O |
CH3COOH |
Molecule |
|
4 |
Glucose |
CH2O |
C6H12O6 |
Molecule |
|
5 |
Methane |
CH4 |
CH4 |
Molecule |
|
6 |
Ammonia |
NH3 |
NH3 |
Molecule |
|
7 |
Hydrogen
peroxide |
HO |
H2O2 |
Molecule |
|
8 |
Iron
Oxide |
Fe2O3 |
----- |
Ionic
Compound |
|
9 |
Sodium
Bromide |
NaBr |
----- |
Ionic
Compound |
|
10 |
Calcium
Chloride |
CaCl2 |
----- |
Ionic
Compound |
3. Formula Unit
The representation of Ionic Compounds which shows the simplest ratio between their ions is called Formula Unit. |
Explanation
The simplest ratio between Na+1 and Cl-1
in the whole crystal lattice of Sodium Chloride is 1:1 so its formula is NaCl.
Define the following terms with examples |
I. Molecular Mass
The sum of the relative atomic masses of all the atoms of a molecular formula is called Molecular Mass. |
Explanation
Molecular mass is also called relative molecular mass. For example, the molecular formula of Acetylene (a gas used for welding purposes) is C2H2; its molecular mass can be determined as
The molecular mass of C2H2
= 2 (At.mass of Carbon) + 2 (Atomic mass of Hydrogen)
= 2 (12amu) + 2 (1.008amu)
= 24 + 2.016
= 26.016 amu
Similarly, the molecular masses of H2O, CO2, and H2SO4 are 18amu, 44amu, and 98amu respectively.
ii. Gram Molecular Mass
The molecular masses of the molecules when expressed in grams is called the Gram molecular mass of that molecule. |
Explanation
For gram molecular mass, we use the unit of “Gram” i.e. g.
For example, the molecular formula of Benzene is C6H6; its gram molecular mass can be determined as
Gram Molecular mass of C6H6
= 6 (At.mass of C in g) + 6 (At.mass of H in g)
= 6 (12g) + 6 (1.008g)
= 72 + 6.048
= 78.048 g
Similarly, the gram molecular masses of H2O, CO2, and H2SO4 are 18g, 44g, and 98g respectively.
iii. Formula Mass
The molecular masses of the molecules when expressed in grams is called the Gram molecular mass of that molecule. |
The sum of the relative atomic masses of all the atoms of a formula unit is called Formula Mass.
Explanation
For the ionic compounds, such as NaCl, which don’t have molecules, we calculate a formula mass based on the empirical formula of the compound. For example, we now calculate the formula mass of NaCl as follows
Formula mass of NaCl
= (At.mass on Na) + (At.mass of Cl)
= 23 amu + 35.5 amu
= 58.5amu
iv. Gram Formula Mass
The formula masses of the formula units when expressed in grams is called the Gram formula mass of that ionic compound. |
Gram Formula mass of NaCl
= (At.mass on Na in g) + (At.mass of Cl in g)
= 23 g + 35.5 g
= 58.5g
Similarly, the gram atomic mass of CaCl2 is 111g.
Example: Calculate
I. The molecular mass of C6H12O6 in grams.
ii. The formula mass for MgCl2 in grams.
i. Molecular mass of C6H12O6 in grams:
= 6 (At.mass of C in g) + 12 (At.mass of H in g) + 6 (At.mass of O in g)
= 6 (12 g) + 12 (1 g) + 6 (16 g)
= 72 g + 12 g + 96 g
= 180 g
ii. Formula mass of MgCl2 in grams:
= 1 (At.mass of Mg in g) + 2 (At.mass of Cl in g)
= 1 (24 g) + 2 (35.5 g)
= 24 g + 71 g
= 95 g
What do you understand by the term |
1. Mole
The amount of substance that contains Avogadro’s Number (6.022×1023) is called Mole. |
Or mole can be quantitatively defined as
The atomic mass or molecular mass or formula mass of a substance expressed in grams is called a mole. |
Explanation
In our daily life, we use the term dozen to express a quantity that is 12. Similarly, gross is another indication of the quantity of 144 similar things. In the same manner, chemists use the term mole to express a definite quantity for counting atoms, molecules, and ions. Thus mole is the counting unit mostly used by chemists to measure the amount of substance.
In simplest words, we can say that mole is the atomic mass of that element in grams or the molecular mass of a compound in grams.
For example,
1 mole of Hydrogen = 1g of Hydrogen
1 mole of Oxygen = 16g of Oxygen
Similarly, one mole of a molecule is the molecular mass in grams (called Molar Mass).
For example,
1 Mole of H2O = 18g of Water
1 mole of CO2 = 44g of CO2
The formula for the Calculation of mole
The number of moles (n) can be calculated by the following formula
- Number of moles (n) = mass (in grams)/ Molar mass or
- Number of moles = No of atoms or molecules / Avogadro’s No
2. Avogadro's number (NA)
The number of atoms, molecules, or ions in one mole of a substance is always constant at 6.022×1023; the number 6.022×1023 is called Avogadro’s number. |
Explanation
An Italian scientist named Amedeo Avogadro experimentally proved that one mole of any substance (atom, molecule, or ion) has 6.022×1023 atoms, molecules, or ions. It means that the number of atoms or molecules is independent of mass.
For example,
1 mole of H = 1g of Hydrogen = 6.022×1023 atoms
1mole of O = 16 g of Oxygen = 6.022×1023 atoms
Similarly, For molecules
1 mole of CO2 = 44g of Carbon-di-oxide = 6.022×1023 molecules.
1 mole of H2O = 18g of Water = 6.022×1023 molecules.
0 Comments:
Post a Comment