Chapter 3 Atoms And Molecules Long Answer Type Question And Answers
Question 1. State the postulates of Dalton’s atomic theory.
Answer.
The postulates of Dalton’s atomic theory are:
- Matter consists of very tiny particles calledatoms.
- Atoms are of indivisible nature whichcannot be created or destroyed in a chemical reaction.
- Mass and chemical properties of atoms of agiven element are identical.
- Different element atoms have differentmasses and chemical properties.
- Compounds are formed by combining atomsin the ratio of small whole numbers.
- In a given compound, the relative numberand kinds of atoms are constant.
Question 2. What are the fundamental rules of writing the chemical formula?
Answer.
There are three fundamental rules of writing chemical formula:
Read and Learn More NEET Foundation Long Answer Questions
- The valencies of the elements must balance.
- When a compound contains both metal and non-metal elements the name of metal comes first. Example: Sodium Chloride (NaCl)
- In poly-atomic ion compounds, the ion is enclosed in bracket before writing the formula to indicate the ratio. In case the ion is mono-atomic then bracket is not required.
Question 3. What does the Dalton’s theory explain? How is it different from modern atomic theory?
Answer.
Dalton’s Atomic theory explains that:
- All matter is made of atoms. Atoms are indivisible and indestructible.
- All atoms of a given element are identical in mass and properties
- Compounds are formed by a combination of two or more different kinds of atoms.
- A chemical reaction is an arrangement of atoms.
Modern atomic theory is, of course, a little more involved than Dalton’s theory but the essence of Dalton’s theory remains valid. Today we know that atoms can be destroyed via nuclear reactions but not by chemical reactions. Many heretofore unexplained chemical phenomena were quickly explained by Dalton with his theory. Dalton’s theory quickly became the theoretical foundation of chemistry.
Question 4. What does a chemical formula indicate?
Answer.
Chemical Formula:
The chemical formula of a compound represents its chemical composition.
A chemical formula essentially indicates 2 things:
- The elements which constitutes thatcompound and the number of each element in it.
- The number of each constituent.
The atoms of the elements are indicated by the symbols and the number is indicated as a subscript with the symbol.
