Some Basic Concepts of Chemistry Notes

Some Basic Concepts of Chemistry Notes

Chemistry is the branch of science that deals with the properties, structure, and composition of matter. There are a large number of branches for Chemistry. Some of them are:
Inorganic Chemistry                           Organic Chemistry
Physical Chemistry                            Analytical Chemistry
Polymer Chemistry                            Biochemistry
Medicinal Chemistry                          Industrial Chemistry
Hydrochemistry                                  Electrochemistry
Green Chemistry

Some Basic Concepts of Chemistry Notes

Matter: Matter is anything that occupies space, has a definite mass, and can be perceived by any of our sense organs. Based on the physical state we can divide matter into different categories.
Solid-State                                          Liquid State
Gaseous State                                    Plasma State
Bose-Einstein Condensate             Fermionic condensate

Classification of Matter: On the basis of Matter composition it can be divided into two categories:

  • Pure Substances
  • Mixtures

Pure substances are made up of the same type of particles. E.g. sodium (Na), Potassium (K), Hydrogen (H), Oxygen (O), Helium (He), Carbon dioxide (CO2), water (H2O), ammonia (NH3), cane sugar (C12H22O11), etc.
These are of two types:

  • Elements
  • Compounds

Elements are pure substances that contain only one type of particle. These particles may be atoms or molecules. For eg: Hydrogen, Nitrogen, Sodium, Potassium, Lithium, Calcium, Phosphorus, etc.

Compounds are pure substances that contain more than one type of atoms. E.g. CO2, H2O, NH3, H2SO4, etc.

Mixtures are made up of two or more types of particles. E.g. all types of solutions, gold ornaments, seawater, muddy water, air, etc.
There are two types of mixtures:

  • Homogeneous Mixture
  • Heterogeneous Mixture

Homogeneous Mixture: Mixture with uniform distribution of particles or mixture with no visible (separation) boundaries of particles. For eg. all types of solutions, water in milk, ink in water, air, etc.

Heterogeneous Mixture: Mixture with no uniform distribution of particles or mixture with visible separation boundaries. For eg. Salt in water, oil in water, soil, etc.

Mass: Mass of a substance is the amount of matter present in it. Its SI unit is the kilogram (kg).

Weight: Weight is the force exerted by gravity on an object. Its SI unit is the newton (N).

  • The mass of a substance is constant whereas its weight may vary from one place to another due to change in gravity.

 Volume (V): It is the space occupied by a body. Its SI unit is m3 (cubic meter). Other units are cm3 (cubic centimeter), mL, L, etc.
1 m3 = 106cm3                 1 cm3 = 1 mL   
1 L = 103 cm3                         1 dm3 = 103 cm3
Density (d): Density of a substance is its amount of mass present in unit volume.
Density = mass/volume.
Its SI unit is kg/m3.
It is commonly expressed in g/cm3.
Temperature: It is the degree of hotness or coldness of a body. It is commonly expressed in degrees Celsius (0C). Other units are degrees Fahrenheit (0F), Kelvin (K), etc. its SI unit is Kelvin (K).
Degree Celsius and degree Fahrenheit are related as:
0F = 9/5(0C) + 32
Degree Celsius and Kelvin are related as:
K = 0C + 273.15
Standard Temperature Pressure (STP): 0 0C (273.15 K) temperature and 1 atm pressure.
Normal Temperature Pressure (NTP): 20 0C (293.15 K) temperature and 1 atm pressure. Standard Ambient Temperature Pressure (SATP): 25 0C (298.15 K) temperature and 1 atm pressure.
The SI system has seven base units which pertain to a few fundamental scientific quantities

Base Physical Quantity Symbol for quantity Name of SI units The symbol for SI units
Length   l  Metre m
Mass m kilogram kg
Time t Second s
Electric current I Ampere A
Thermodynamic temperature T Kelvin k
Amount of substance n Mole mol

Precision: It indicates how closely repeated measurements match each other.

Accuracy: It indicates how closely a measurement matches the correct or expected value.

Scientific Notation: Any number can be represented in the form where n is an exponent having positive or negative values and N can vary between 1 to 10. Expressing a number in form N × 10n, and N can vary between 1 to 10.

Significant figures: These are meaningful digits that are known with certainty. The uncertainty is indicated by writing the certain digits and the last uncertain digit. Thus, if we write a result as 11.2 mL, we say the 11 is certain and 2 is uncertain and the uncertainty would be 1 in the last digit.
There are certain rules for determining the number of significant figures. These are:

  1. All non-zero digits are significant. For example, in 285 cm, there are three significant figures and in 0.25 mL, there are two significant figures.
  2. Zeros preceding to first non-zero digit are not significant. Such zero indicates the position of the decimal point. Thus, 0.03 has one significant figure and 0.0052 has two significant figures.
  3. Zeros between two non-zero digits are significant. Thus, 2.005 has four significant figures.
  4. Zeros at the end or right of a number are significant if they are on the right side of the decimal point; otherwise, they are not significant. For example, 0.200 g has three significant figures.
  5. Exact numbers have an infinite number of significant figures. For example, in 2 balls or 20 eggs, there are infinite significant figures since these are exact numbers and can be represented by writing an infinite number of zeros after placing a decimal i.e., 2 = 2.000000 or 20 = 20.000000

When numbers are written in scientific notation, the number of digits between 1 and 10 gives the number of significant figures. For e.g. 4.01×102 has three significant figures, and 8.256 × 10–3 has four significant figures.


Some Basic Concepts of Chemistry Notes

Laws of Chemical Combinations:

Law of Conservation of Mass: Antoine Lavoisier established the Law of Conservation of Mass. It states that matter can neither be created nor destroyed.
In other words, we can say that during any physical or chemical change, the total mass of reactants is equal to the total mass of products. For eg.
Consider the reaction 2H2 + O2 → 2H2O
Here 4 g of H2 combines with 32 g of O2 to form 36 g of water.
Total mass of reactants = 4 + 32 = 36g. The total mass of products = 36 g

Law of Definite Proportions: A given compound always contains the same elements in the same proportion by mass.
For Example, Carbon dioxide can be formed in the atmosphere by various methods like respiration, burning of fuels, the reaction of metal carbonates and bicarbonates with acid, etc. All these samples of CO2 contain only two elements Carbon and Oxygen combined in a mass ratio of 3:8.

Law of Multiple Proportions: When two elements combine to form two or more compounds, then the different masses of one element, which combine with a fixed mass of the other, bear a simple ratio to one another.
Hydrogen combines with oxygen to form two compounds – water and hydrogen peroxide.                       

Hydrogen + Oxygen → Water     
       2g            16g          18g
Hydrogen + Oxygen → Hydrogen Peroxide    
      2g               32g                34g
Here, the masses of oxygen (i.e. 16 g and 32 g) which combine with a fixed mass of hydrogen (2g) bear a simple ratio, i.e. 16:32 or 1: 2.

Gay Lussac’s Law: Under similar conditions of temperature and pressure whenever gases combine together, they do so in terms of volume.
e.g.,  2 H2 (g)  +  O2 (g)  →  2 H2O (g)     
          2 vol         1 vol           2 Vol     (at same T, P)

Avogadro’s Law: Under similar conditions of temperature and pressure equal volume of all gases contains an equal number of molecules.
For example: If we take 10L each of NH3, N2, O2, and CO2 at the same temperature and pressure, all of them contain the same number of moles and molecules.

Dalton’s atomic theory: In 1808, Dalton published ‘A New System of Chemical Philosophy’ in which he proposed the following:
(i) Matter consists of indivisible atoms.
(ii) All the atoms of a given element have identical properties including identical mass. Atoms of different elements differ in mass.
(iii) Compounds are formed when atoms of different elements combine in a fixed ratio.
(iv) Chemical reactions involve the reorganization of atoms. These are neither created nor destroyed in a chemical reaction.



Some Basic Concepts of Chemistry Notes

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