3 marksShort AnswerSection B

(a) List two advantages of adopting the atomic number of an element as the basis of classification of elements in the Modern Periodic Table. (b) Write the electronic configurations of the elements X (atomic number 13) and Y (atomic number 20).

Metals and Non-metals

Classification of Elements and Electronic Configuration

Official Answer

(a) Two advantages of adopting atomic number as the basis of classification are:

(i) It provides a more fundamental property of an element than atomic mass, as the atomic number is unique to each element and increases by 1 from one element to the next.

(ii) It explains the periodicity in the properties of elements by relating them to the electronic configuration (number of valence electrons).

(b) Electronic configurations:

Element $X$ (Atomic Number $13$ ): $2, 8, 3$
Element $Y$ (Atomic Number $20$ ): $2, 8, 8, 2$

Atomic NumberFundamental propertyElectronic configuration2, 8, 32, 8, 8, 2

Marking Scheme

1Two advantages of atomic number classification (2 marks)
2Correct electronic configuration of X (0.5 marks)
3Correct electronic configuration of Y (0.5 marks)

Hint

Atomic number represents the number of electrons. Fill shells in the order K(2), L(8), M(8 or 18), N(2...).

Quick Oral Answer

What is the atomic number of an element? It is the number of protons present in the nucleus of an atom, which is also equal to the number of electrons in a neutral atom.

Analysis & Explanation

The atomic number is the basis of the Modern Periodic Table. Element $X$ with atomic number $13$ is Aluminium ( $Al$ ). As seen in the NCERT text (Section 3.2.1), Aluminium reacts with oxygen to form $Al_2O_3$ . Its configuration $2, 8, 3$ shows it has 3 valence electrons. Element $Y$ with atomic number $20$ is Calcium ( $Ca$ ). The text (Section 3.2.2) notes that Calcium reacts with water to form $Ca(OH)_2$ and hydrogen gas. Its configuration $2, 8, 8, 2$ shows it has 2 valence electrons, placing it in Group 2.

Common Mistakes

1Writing the configuration of Calcium (20) as 2, 8, 10. Remember that the outermost shell cannot have more than 8 electrons unless it is the only shell.
2Confusing atomic number with atomic mass.

Interesting Facts

Aluminium (X) is the most abundant metal in the Earth's crust, while Calcium (Y) is essential for bone health and reacts with water to produce hydrogen bubbles that make the metal float.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2022?

This question carries 3 marks in the CBSE Class 10 Science 2022 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Metals and Non-metals" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Classification of Elements and Electronic Configuration" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2022 paper?

This is a Short Answer question from Section B in the CBSE Class 10 Science 2022 paper.