Aman was discussing the structure of atom with his classmates. Class 9

Aman was discussing the structure of atom with his classmates. Class 9

Question 1.

Aman was discussing the structure of atom with his classmates. During the discussion, he learnt that an element X has a mass number of 35 and contains 18 neutrons. Based on this information, answer the following questions: Class 9

(i) How many electrons and protons does element X have?

(ii) What is its atomic number?

(iii) Identify the element X.

(iv) Write its electronic configuration.

(v) How many valence electrons does it have?

(vi) What will be the mass number if two neutrons are added to its nucleus?

(vii) What will be the relation of X with the new atom?

Answer:

(i)

1. Mass number = 35, number of neutrons = 18.
2. Number of protons = Mass number - Number of neutrons = 35 - 18 = 17.
3. Since the atom is neutral, number of electrons = number of protons =17.
4. Answer: Element X has 17 protons and 17 electrons.

(ii) Atomic number = Number of protons = 17.

(iii) The element with atomic number 17 is Chlorine (Cl).

(iv)

1. Atomic number = 17, so 17 electrons.
2. K-shell: 2 electrons, L-shell: 8 electrons, M-shell: 7 electrons.
3. Electronic configuration = 2, 8, 7.

(v) The outermost (valence) shell is the M-shell which has 7 electrons. So element X has 7 valence electrons.

(vi)

1. Original neutrons = 18, adding 2 more = 20 neutrons.
2. New mass number = number of protons + new number of neutrons = 17 + 20 = 37.
3. Answer: The new mass number will be 37.

(vii) The original element X has mass number 35 and atomic number 17. The new atom has mass number 37 and atomic number 17 (same, because protons have not changed). Both atoms have the same atomic number (same element - Chlorine) but different mass numbers. Therefore, X and the new atom are isotopes of each other.