Introduction to fundamental concepts of chemistry and some MCQs

 

What are the fundamentals of chemistry

Chemistry is the branch of main science that deals with the study and observation of the chemical composition of matter, their chemical properties and the reaction they take place.

Chemistry starts with the introduction of matter. Matter is any substance made up of atoms or molecules and that has its weight and occupies certain space. Matter has several states. In high school we can be familiar with a few of them, predominantly solid , liquid and gas. Perhaps after gas, plasma. These four are the observable state of matter

Here are classification of state of matter :

1) Observable or fundamental state

--> Solid , Liquid , gas and plasma

2) Non classical or intermediate state

----> Liquid crystal

3) Low temp. State

---->Super conductor, superfluid, bose-einstein condensate, photonic matter etc.

4) High temp. State

-->Degenerate matter, quark matter etc

5) Very high temp. State

6) Other states

--->Super solid, string net fluid, superglass.

Although there are so many states of matter, there is use of only the fundamental states. There is no such practical way to interact and observe the other states. But it should be in our mind for some extra knowledge and later on after your academic period you can study among one of them.

Those were the state of matter now here comes the division of types of matter. Matter are classified into two groups i.e. Pure matter and impure matter.

Pure matter are those that are composed of similar substances in fixed proportion by their weight. They are of two types i.e. elements and compounds.

Impure matter are the uneven mixture of different substances. They are also of two types i.e. homogeneous and heterogeneous mixture.

Electronic configuration of atoms

Atoms are depicted in notebooks with the help of bohr models. But in real life the atoms have the shells in which electrons occur suddenly with any path of moment. The orbit shown in the bohr model is not the path where electrons orbit. There is the division of location of electrons that depicts how many time electrons occur there and density of electrons. Those divisions are called shells. These are made up of subshells or also known as orbitals viz. s, p, d and f. In s-subshell maximum of 2 electrons then in p-subshells maximum of 6 electrons. Similarly add 4 electrons in the preceding subshell to get the maximum number of electrons of succeeding. These subshells help to show the electronic configuration of atoms. But it requires the bohr model as well.

Just remember this thing.

                         

Shells or Orbit	Subshells or orbitals
K(1)- 2 electrons	s
L(2)- 8”	S and p
M(3)- 8”	S, p, and d
N(4)- 8”	S, p, d and f

Now we should understand that in the K orbit [ that can hold max of 2 electrons ] only(s)orbital occurs and so on in the other orbit shown above.

Now let's go towards the way of expressing electronic configuration. Lets Calcium as an example.

                                                                                   

                                                                                   (2)    (8)       (8)     (2)

                                                                                    K      L         M      N

According to subshells its electronic configuration is 1s2,2s22p6,3s23p6,4s2  

Where 1=K, 2=L, 3=M, 4=N and the subscripted numbers show the number of electrons. For example in 2 which is L there are two subscripted numbers 2 and 6 and if you add those you will get 8 which means there is the capacity of 8 electrons of L shell.

What is valency ?

Now any chemical substance takes part in chemical reactions with respect to their combining capacity with other substances. The combining capacity of elements or radicals( the group of charged particles either positively or negatively that acts as a single unit) with other elements or radicals is known as their valencies. In atoms valency is determined by observing the electrons in the last orbit of the atom which are known as valence electrons . Except the K orbit all orbit wants to take 8 electrons this property is known as octet rule whereas the K shell wants to take only two electrons and this property is known as duplet rule. So if the valence electrons are greater than 4 then they gain some electrons from other atoms to complete their octet and get negatively charged due to greater number of electrons than protons. If the valence electrons are less than 4  then the atom donates those electrons and gets positively charged due to a greater number of protons than the electrons. So the valency of an atom is obtained by knowing the number of electrons that are received or donated.

Variable valencies

Valencies of some metals don’t remain constant. The power of elements to show different valencies with different elements is known as variable valencies. 

Example : Iron has two valencies i.e. 2[ferrous(Fe++ )]and 3[Ferric(Fe+++)]

Copper,Gold,Mercury , Lead are some examples of variable valency elements.

Chemical reactions

Now let's discuss about the change. There are two types of change i.e. physical change and chemical change. Physical change is the temporary change in which no new substance is formed such as melting of ice, water cycle etc whereas chemical change is the permanent change in which new substance is formed such as burning of paper, digestion process etc.

The chemical change that practices addition, decomposition or displacement of chemical substances is known as chemical change.

The types of chemical reaction are:

1. Additional Reaction-

                        This reaction involves a combination of reactants to form a single product. Reactants are the substances that take part in chemical reactions whereas products are the substances produced after the reaction. The example of additional reaction is:

                                         Na + Cl2  —-------------> 2NaCl

2. Decomposition Reaction -

                           This reaction involves a deformation or separation of chemical components.

For example:

                                     CaCO3 —------------------> CaO + CO2

3. Displacement Reaction-

                           This reaction involves a displacement or exchange of chemical components’ place. For example:

                                 Fe + CuSO4 —-------------------> Cu + FeSO4

4. Acid-base Reaction- 

             This reaction occurs between acid and base in which as a result, salt and water are formed. For example:

               H2SO4 + 2NaOH —----------------------> Na2SO4 + 2H2O

Note: All the metallic hydroxide(OH- ) are bases 

Basic concepts of chemistry all formulas

First 20 elements with their electronic configuration.

Some positively charged radicals.

Note : Most metallic ions are positively charged.

Some negatively charged radicals.

Note: Most non-metallic ions are negatively charged.

Some chemical formulae of compounds.

Fundamental concepts of chemistry MCQs

1. Which of the following is NOT a chemical reaction?

a) Rusting of iron

b) Burning of paper

c) Melting of ice

d) Cooking an egg

2. What is the valency of oxygen?

a) 1

b) 2

c) 3

d) 4

3. What is the chemical formula for table salt?

a) NaCl

b) HCl

c) H2SO4

d) CO2

4. Which state of matter has a definite shape and volume?

a) Solid

b) Liquid

c) Gas

d) Plasma

5. What is the electronic configuration of oxygen?

a) 1s2 2s2 2p4

b) 1s2 2s2 2p2

c) 1s2 2s1

d) 1s2 2s2 2p5

6. How many valence electrons does carbon have?

a) 1

b) 2

c) 4

d) 6

7. What is the chemical formula for water?

a) CO2

b) H2SO4

c) H2O

d) NaCl

8. What is the state of matter in which the particles are arranged in a regular, repeating pattern?

a) Solid

b) Liquid

c) Gas

d) Plasma

9. Which of the following elements has the highest valency?

a) Carbon

b) Nitrogen

c) Oxygen

d) Fluorine

10. What is the electronic configuration of sodium?

a) 1s2 2s2 2p6 3s1

b) 1s2 2s2 2p6

c) 1s2 2s1

d) 1s2 2s2 2p5