Chemistry
Assertion (A): The valency of an element is its combining capacity with an atom of another element.
Reason (R): Elements take part in chemical combination to acquire the electronic configuration of the nearest noble gas.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Answer
Both A and R are true but R is not the correct explanation of A.
Explanation — Valency of an element is the combining capacity of that element with other elements and is equal to the number of electrons that take part in a chemical reaction. Hence the assertion (A) is true. The atoms of all elements, other than the inert gases, combine to attain a stable configuration of nearest noble gas. Hence the reason (R) is true.
However, reason (R) is not the correct explanation of assertion (A), because valency is defined by how many electrons are involved in bonding, not by why the atom bonds (which R explains). Hence, while both statements are correct individually, reason (R) doesn’t directly explain assertion (A).
Related Questions
Assertion (A): Neon is a noble gas.
Reason (R): Neon is not very reactive due to its small size.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Assertion (A): The properties of an ion are different from that of the parent atom.
Reason (R): Atoms and ions differ with respect to the number of neutrons and protons in them.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Some main features of the structure of an atom are :
(i) Atoms of all the elements (except hydrogen) are made up of three fundamental (sub-atomic) particles: electrons, protons and neutrons. (Hydrogen atom lacks neutrons).
(ii) The nucleus is located at the centre of the atom. It contains protons and neutrons, which account for the total mass of that atom.
(iii) The nucleus is positively charged due to the presence of protons in it.
(iv) The electrons are outside the nucleus and have negligible mass.
Answer the following:
(a) What is the charge of nucleus ? Give reason.
(b) Atom is positively charged, negatively charged or neutral ? Why ?
(c) Why do only protons and neutrons account for the total mass of an atom ?
(d) What do you mean by orbits ?
(e) Draw a figure showing the 3 fundamental particles in an atom.
Electronic configuration is the distribution of electrons in the various energy shells of an atom. It is based on the Bohr-Bury scheme, which states that :
- The maximum number of electrons that can be accommodated in a shell is given by 2n2, where n is the shell number.
- The outermost shell cannot have more than 8 electrons.
- A new shell starts filling once the inner shell acquires eight electrons.
Based on the information given above, answer the following questions:
(a) Write the electronic configuration of an atom X with atomic number 19.
(b) Draw the orbital diagram of the ion formed by atom X.
(c) Draw the complete orbital diagrams of the atoms 35Cl and 37Cl.
(d) Which fundamental particle differs in the atoms mentioned in part (c)?
(e) State the general term used for the atoms given in part (c).