(i) Write the electronic configurations of the following ions: (a) H– (b) Na+ (c) O2– (d) F–
(ii) What are the atomic numbers of elements whose outermost electrons are represented by (a) 3s1 (b) 2p3 and (c) 3p5?
(iii) Which atoms are indicated by the following configurations? (a) [He] 2s1 (b) [Ne] 3s2 3p3 (c) [Ar] 4s2 3d1.
(ii) What are the atomic numbers of elements whose outermost electrons are represented by (a) 3s1 (b) 2p3 and (c) 3p5?
(iii) Which atoms are indicated by the following configurations? (a) [He] 2s1 (b) [Ne] 3s2 3p3 (c) [Ar] 4s2 3d1.
Solution and Explanation
∴ Electronic configuration of H - = 1s2
(b) Na + ion The electronic configuration of Na atom is 1s2 2s2 2p6 3s1 . A positive charge on the species indicates the loss of an electron by it.
∴ Electronic configuration of Na+ = 1s2 2s2 2p6 3s0 or 1s2 2s2 2p6
(c) O2- ion The electronic configuration of 0 atom is 1s2 2s2 2p4 . A negative charge on the species indicates that two electrons are gained by it.
∴ Electronic configuration of O2- ion = 1s22s2 p6
(d) F- ion The electronic configuration of the F atom is 1s22s22p5 . A negative charge on the species indicates the gain of an electron by it.
∴ Electron configuration of F- ion = 1s22s22p6
(ii) (a) 3s1 Completing the electron configuration of the element as 1s22s22p63s1.
∴ Number of electrons present in the atom of the element = 2 + 2 + 6 + 1 = 11
∴ The atomic number of the element = 11
(b) 2p3 Completing the electron configuration of the element as 1s22s22p3.
∴ Number of electrons present in the atom of the element = 2 + 2 + 3 = 7
∴ The atomic number of the element = 7
(c) 3p5 Completing the electron configuration of the element as 1s22s22p5.
∴ Number of electrons present in the atom of the element = 2 + 2 + 5 = 9
∴ The atomic number of the element = 9
(iii) (a) [He] 2s1 The electronic configuration of the element is [He] 2s1 = 1s22s1.
∴ The atomic number of the element = 3 Hence, the element with the electronic configuration [He] 2s1 is lithium (Li).
(b) [Ne] 3s23p3 The electronic configuration of the element is [Ne] 3s23p3= 1s 2 2s22p6 3s2 3p3 .
∴ The atomic number of the element = 15 Hence, the element with the electronic configuration [Ne] 3s23p3 is phosphorus (P).
(c) [Ar] 4s23d1 The electronic configuration of the element is [Ar] 4s2 3d1= 1s2 2s22p63s23p6 4s23d1.
∴ The atomic number of the element = 21 Hence, the element with the electronic configuration [Ar] 4s23d1 is scandium (Sc).
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Concepts Used:
Structure of Atom
Atomic Structure:
The atomic structure of an element refers to the constitution of its nucleus and the arrangement of the electrons around it. Primarily, the atomic structure of matter is made up of protons, electrons and neutrons.
Dalton’s Atomic Theory
Dalton proposed that every matter is composed of atoms that are indivisible and indestructible.
The following are the postulates of his theory:
- Every matter is made up of atoms.
- Atoms are indivisible.
- Specific elements have only one type of atoms in them.
- Each atom has its own constant mass that varies from element to element.
- Atoms undergo rearrangement during a chemical reaction.
- Atoms can neither be created nor be destroyed but can be transformed from one form to another.
Cons of Dalton’s Atomic Theory
- The theory was unable to explain the existence of isotopes.
- Nothing about the structure of atom was appropriately explained.
- Later, the scientists discovered particles inside the atom that proved, the atoms are divisible.
Subatomic Particles
- Protons - are positively charged subatomic particles.
- Electron - are negatively charged subatomic particles.
- Neutrons - are electrically neutral particles and carry no charge
Atomic Structure of Isotopes
Several atomic structures of an element can exist, which differ in the total number of nucleons.These variants of elements having a different nucleon number (also known as the mass number) are called isotopes of the element. Therefore, the isotopes of an element have the same number of protons but differ in the number of neutrons. For example, there exist three known naturally occurring isotopes of hydrogen, namely, protium, deuterium, and tritium.