October 21, 2021

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Some Basic Concepts in Chemistry- Chapter Review

Department of Chemistry

Chemistry is a science that deals with atoms and molecules. By definition, it’s the study of composition, structure and it interprets the properties of matter. It has many sub-branches, like biochemistry, nanochemistry, organic chemistry, inorganic chemistry and so on. Each of them varies in concept but is similar in general chemistry. 

Chemistry is not limited to a textbook but has a massive application in daily life, as all are aware of. This chapter belongs to the class 11 chemistry of NCERT textbook. As the name suggests, some basic concepts are explained in this chapter to understand better what chemistry is.

In this article, we will go through some important topics mentioned in the chapter. 

Matter and its properties

The matter is defined explicitly as anything that has mass and occupies space. Three physical states that matter exists:- Solid, liquid and gas. Again, at the macroscopic level, it is classified as pure substance and mixtures. A pure substance is composed of only one substance, whereas mixtures comprise one or more substances. Pure substances and mixtures have classifications.

Pure substances : 

  1. Elements
  2. Compounds

Mixtures

  1. Homogenous
  2. Heterogeneous

Physical properties and chemical properties are the two types of properties.

Physical Properties

Physical properties are measured or observed without affecting the substance’s identity or composition. For instance, colour, fragrance, melting point, boiling point, density, other physical qualities etc.

 Chemical Properties

Chemical properties can be observed in chemical reactions for specific substances. Some examples include flammability, toxicity, the heat of combustion, pH, decay rate etc.

Laws of chemical combination

Law of Conservation of Mass (Lavoisier, 1774)

This law states that, in a chemical reaction, the mass of reactants consumed and the mass of the products formed is the same. Hence, mass is conserved. 

Law of Definite Proportions (Proust, 1799)

The law of definite proportions states that the mass proportions of the elements in a composite sample are always the same.

Law of Multiple Proportions(Dalton, 1803)

The law of multiple proportions states that when two elements are combined to form more than one compound, then the masses of one element that combine with the other element are in the ratio of small whole numbers. This law was proposed by Dalton.

Law of Reciprocal Proportions (Richter, 1792)

Richter proposed the law and stated that if two different elements are combined with the fixed mass of the third element, their combined mass ratio is the same or a simple multiple of their combined mass. 

Gay Lussac’s Law of Gaseous Volumes

The law was proposed by Gay Lussac in 1808 and stated that “a simple whole number can represent the relationship between the volume of a gaseous reactant and a product.”

Avogadro Law

Avogadro law states that the equal volumes of gases at an equivalent temperature and pressure should contain an equal number of molecules.

Dalton’s Atomic Theory

The main postulates of the theory are:-

  1. The matter is composed of tiny, individual particles called atoms.
  2. Atoms of the same element are alike in their respective size and mass.
  3. Atoms of different elements possess different sizes, shapes, masses, and chemical properties.
  4. Compounds are formed when atoms of different elements are combined in a fixed ratio.
  5. Atoms can neither be created nor destroyed.

Mole concept

A mole is defined as the amount of substance that comprises an equal number of elementary particles (atoms, molecules or ions) as the number of atoms present in 12 g of carbon (C-12).

Molecular Mass

Molecular Mass = average relative mass of one molecule / 1 / 12th x mass of C-12 atom

Molarity

It is the concentration of any substance existing in the solution. Or it can be defined as the moles of solute per unit volume of solution in litres. Mathematically, 

Molarity M =  (Number of moles of the solute present)/(Volume of solution in Litre)  

Molality

The definition of molality is the number of moles of solute dissolved per 1000 g (1 kg) of solvent. Molality is expressed as ’m’ and mathematically written as,

Molality m =  (Number of moles of solute)/(Weight of solvent in kg)

Note

There are many more concepts included in this chapter. A few basic concepts of chemistry have been explained above. You can refer more to Myncert Books for Class 11 Chemistry. Concepts are conveyed simply and understandably.