3 marksShort AnswerSection A

Write the number of periods and groups in the Modern Periodic Table. How does the metallic character of elements vary on moving (i) from left to right in a period, and (ii) down a group ? Give reason to justify your answer.

Q: Write the number of periods and groups in the Modern Periodic Table. How does the metallic character of elements vary on moving (i) from left to right in a period, and (ii) down a group ? Give reason to justify your answer.

1. **Number of Periods and Groups:** - There are $7$ periods and $18$ groups in the Modern Periodic Table. 2. **Variation of Metallic Character:** - **(i) From left to right in a period:** Metallic character **decreases**. - *Reason:* As we move from left to right across a period, the nuclear charge increases due to the addition of protons in the nucleus, while the electrons are added to the same valence shell. This increases the effective nuclear charge, pulling the valence electrons more strongly towards the nucleus. Consequently, the tendency of atoms to lose electrons (electropositive character) decreases. - **(ii) Down a group:** Metallic character **increases**. - *Reason:* As we move down a group, a new electronic shell is added at each successive step, which increases the atomic size. The distance between the outermost valence electrons and the nucleus increases, reducing the nuclear force of attraction on these valence electrons. Thus, the tendency to lose electrons increases.

Metals and Non-metals

Physical and Chemical Properties of Metals

Official Answer

Number of Periods and Groups:

There are $7$ periods and $18$ groups in the Modern Periodic Table.

Variation of Metallic Character:

(i) From left to right in a period: Metallic character decreases.
Reason: As we move from left to right across a period, the nuclear charge increases due to the addition of protons in the nucleus, while the electrons are added to the same valence shell. This increases the effective nuclear charge, pulling the valence electrons more strongly towards the nucleus. Consequently, the tendency of atoms to lose electrons (electropositive character) decreases.
(ii) Down a group: Metallic character increases.
Reason: As we move down a group, a new electronic shell is added at each successive step, which increases the atomic size. The distance between the outermost valence electrons and the nucleus increases, reducing the nuclear force of attraction on these valence electrons. Thus, the tendency to lose electrons increases.

7 periods18 groupsmetallic character decreaseseffective nuclear chargemetallic character increasesatomic sizetendency to lose electrons

Marking Scheme

11 Mark: Correctly stating the number of periods ( $7$ ) and groups ( $18$ ) in the Modern Periodic Table.
21 Mark: Correctly stating that metallic character decreases across a period and explaining it in terms of increasing effective nuclear charge.
31 Mark: Correctly stating that metallic character increases down a group and explaining it in terms of increasing atomic size and decreasing nuclear pull.

Hint

Think about how atomic size and nuclear charge change as you move across a period and down a group, and how this affects the ease with which an atom can lose its valence electrons.

Quick Oral Answer

The Modern Periodic Table consists of $7$ horizontal rows called periods and $18$ vertical columns called groups. Metallic character decreases across a period because the nuclear charge increases, making it harder to lose electrons. It increases down a group because atomic size increases, making it easier to lose valence electrons.

Analysis & Explanation

Metallic character refers to the electropositive nature of an element, which is its ability to lose electrons and form positive ions (cations). In Chapter 3, we learn that metals (like sodium and potassium) readily lose electrons to form basic oxides, whereas non-metals tend to gain or share electrons to form acidic oxides.

Across a period, the addition of protons increases the nuclear pull, making it harder for atoms to lose electrons. Hence, elements transition from highly reactive metals (on the left) to metalloids and then to non-metals (on the right).
Down a group, the addition of new shells increases the atomic radius, shielding the valence electrons from the nuclear charge. This makes it easier to lose electrons, thereby increasing metallic character.

Common Mistakes

1Confusing periods with groups (e.g., writing 18 periods and 7 groups).
2Stating that metallic character increases across a period because the number of valence electrons increases.
3Failing to link metallic character to the tendency of an atom to lose electrons.

Interesting Facts

Francium ( $\text{Fr}$ ) is theoretically the most metallic and electropositive element in the periodic table, but because it is highly radioactive and has a very short half-life, cesium ( $\text{Cs}$ ) is practically considered the most reactive stable metal.

The word 'metal' originates from the Greek word 'metallon', which means to mine, quarry, or extract from the earth.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2017?

This question carries 3 marks in the CBSE Class 10 Science 2017 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 "Physical and Chemical Properties of Metals" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2017 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2017 paper.