Chemistry Basics

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Basic Concepts 

Science 

Science word is derived from a Latin word Scientia which means knowledge [1].  It is defined as the observation, identification, experimental investigation and theoretical explanation of natural phenomena [2]. 

According to me it simply can be defined as "The study of matter is called science". Every studies which could not be justified by science is called pseudoscience. It consists of statements, beliefs or practices that are claimed to be both scientific and factual but are incompatible with the scientific methods [3].

Hierarchy of the Science [6]

Science has three major categories which are being taught as courses in our education systems. 

1. Formal Sciences
2. Natural Sciences 
3. Social Sciences 

Natural Sciences

The study of natural phenomena (including cosmological, geological, physical, chemical and biological factors of the universe). It further categorized as Chemistry, Biology and Physics. 
In all these subjects, matter is studied but differently.

Physics 

A branch of science which deals with matter and energy and their interactions [4].

Biology

A branch of science which deals with matter in living form. The word biology is derived from the greek words /bios/ meaning /life/ and /logos/ meaning /study/ and is defined as the science of life and living organisms. An organism is a living entity consisting of one cell e.g. bacteria, or several cells e.g. animals, plants and fungi [5].

Chemistry 

The branch of science which deals with the composition, structure, properties and reactions of matter is called chemistry [7].  

If you have read up til now, then you must know in science, we talking about matter everywhere. So we must know, what is this matter?

Matter

Anything which has mass and occupies space is called matter. Everything is all about matter in chemistry. Therefore, we must categorize it to know what is it all about. Please give it a read with concentration, I hope you will understand. 

Classification of Matter

There are some basic definitions you must know to learn chemistry. 

Substance

Pure form of matter is called substance. For example water is a substance [7].

Element

It is a substance made up of same type of atoms, having same atomic number and it cannot be decomposed into simple substances by ordinary chemical means. It means that each element is made up of same type of atoms that have very specific properties [7]. For example oxygen, hydrogen etc.

List of Elements Commonly Used

Atom

The word atom is derived from a atomos which means indivisible. It is defined as "The smallest particle of an element, which can take part in chemical reaction". It may or may not exist independently. For example, He and Ne etc. have atoms which have independent existence while atoms of H, N and O do not exist independently [8].

Isotopes

Isotopes are different kind of atoms of the same element having same atomic number but different atomic masses. They have equal no of protons and electrons and differ only in number of neutrons. They have same chemical properties because these properties depend upon atomic number and atomic numbers of all the isotopes of an element are same [8]. 

Molecules 

A molecule is the smallest particle of a pure substance which can exist independently. It may contain one or more atoms. The number of atoms in a molecules determines its atomicity.
Types of molecules 
Monoatomic (one atom e.g He), diatomic(two atoms e.g O2), triatomic (three atoms e.g. O3), tetraatomic (four atoms e.g. P4) and polyatomic (more than four e.g. C6H12O6) on the basis of atomicity.   
Homeatomic (same type of atoms e.g O3) and Heteroatomic (different type of atoms e.g. H2O) on the basis of type of atoms [8].

Molecular Ion

Ions are the species that carry either negative or positive charge. When a molecule may lose or gain an electron, it forms a molecular ion. For example CH₄⁺,CO⁺ and N₂⁺. Cationic molecular ions are more abundant than anionic molecular ions [8]. 

Mixture

When two or more elements or compounds mixed up physically without any fixed ratio, they form a mixture [7]. 

Homogeneous Mixture

Mixtures that have uniform composition throughout are called homogeneous mixtures. e.g. air, gasoline, ice-cream. Solutions are also homogeneous mixtures [7].  

Heterogeneous Mixture

Mixtures in which composition is not uniform throughout are called heterogeneous mixtures. e.g. soil, rock and wood. Suspensions are also heterogeneous mixtures [7]. 

Mole

When the molar mass(atomic, molecular or formula mass) of a substance, expressed in grams then it is called as mole. It is considered as secret unit of chemists. The mole is the mass of substance containing the same number of fundamental units as there are atoms in exactly 12 g of ¹²C [9]. It is represented by n. 

Avogadro`s number value is NA=6.02 × 10²³ to find number of fundamental particles.

  Number of molecules (N) = no. of moles (n) × Avogadro`s Number (NA)

Examples 

Calculations of number of molecules in 34 g of H₃PO₄.

Calculation of mass in grams of 10­^-3 moles of water. 

      No. of moles = 10^-3

      Molar mass of water = 18g

      Mass in grams is given by;

                Mass = no. of moles × molar mass

                         = 10^-3 × 18 g

                                     = 0.018g

  So, the mass in grams of 10­^-3 moles of water is 0.018g.

Molarity 

Molarity is the number of moles of solute dissolved per dm³ of the solution. To prepare one molar solution of glucose in water, we take 180g of glucose and add sufficient water to make the total volume of 1 dm³. It is represented by M.  

Molality

Molality is the number of moles of solute in 1000g (1 kg) of the solvent. In order to prepare molal solutions, 180g of glucose is dissolved in 1000g of water

Parts Per Million (ppm)

It is defined as the number of parts (by weight or volume) of the solute per million parts (by weight or volume) of the solution. This unit is used for very low concentrations of solutions, e.g. to express the impurities of substances in water.

Example

Sea water has 5.65 x 10^-3 g of dissolved oxygen in one kg of water. Calculate the concentration of oxygen in sea water in parts per million (ppm). 

I hope you have read and learnt these terms. If you have any questions regarding chemistry of any grade please do ask in comments section. Answers will be posted in "Frequently Asked Questions (FAQs)" section and will notify you in your comment`s reply. Thanks!! Stay Blessed.

Best of Luck 👍

References 

1. Harper, Douglas. "science". Online Etymology Dictionary. Retrieved September 20, 2014.
2. https://explorable.com/definition-of-science
3. Cover JA, Curd M, eds. (1998), Philosophy of Science: The Central Issues, pp. 1–82
4. https://www.merriam-webster.com/dictionary/physics
5. https://www.ntnu.edu/biology/about-us/what-is-biology
6. https://en.wikipedia.org/wiki/Branches_of_science#/media/File:The_Scientific_Universe.png
7. Punjab Textbook Chemistry 9th Class.
8. Punjab Textbook Chemistry 11th Class.
9. http://chemistry.bd.psu.edu/jircitano/mole.html