3 marksShort AnswerSection A

How many groups and periods are there in the modern periodic table? How do the atomic size and metallic character of elements vary as we move: (a) down a group and (b) from left to right in a period

Q: How many groups and periods are there in the modern periodic table? How do the atomic size and metallic character of elements vary as we move: (a) down a group and (b) from left to right in a period

In the Modern Periodic Table, there are **18 vertical columns called groups** and **7 horizontal rows called periods**. ### Variation of Atomic Size and Metallic Character: #### (a) Down a Group: 1. **Atomic Size**: **Increases**. As we move down a group, new electronic shells are progressively added. This increases the distance between the outermost shell and the nucleus, which outweighs the effect of the increased nuclear charge. 2. **Metallic Character**: **Increases**. With the increase in atomic size, the valence electrons experience less electrostatic attraction from the nucleus. Consequently, the tendency of an atom to lose electrons (metallic character) increases. #### (b) From Left to Right in a Period: 1. **Atomic Size**: **Decreases**. As we move from left to right, electrons are added to the same valence shell while the nuclear charge (number of protons) increases. This stronger nuclear pull draws the electrons closer to the nucleus, reducing the atomic radius. 2. **Metallic Character**: **Decreases**. The increase in effective nuclear charge across a period makes it harder for atoms to lose their valence electrons. Hence, the tendency to lose electrons decreases, leading to a decrease in metallic character.

Metals and Non-metals

Metallic Character and Periodic Trends

Official Answer

In the Modern Periodic Table, there are 18 vertical columns called groups and 7 horizontal rows called periods.

Variation of Atomic Size and Metallic Character:

#### (a) Down a Group:

Atomic Size: Increases. As we move down a group, new electronic shells are progressively added. This increases the distance between the outermost shell and the nucleus, which outweighs the effect of the increased nuclear charge.
Metallic Character: Increases. With the increase in atomic size, the valence electrons experience less electrostatic attraction from the nucleus. Consequently, the tendency of an atom to lose electrons (metallic character) increases.

#### (b) From Left to Right in a Period:

Atomic Size: Decreases. As we move from left to right, electrons are added to the same valence shell while the nuclear charge (number of protons) increases. This stronger nuclear pull draws the electrons closer to the nucleus, reducing the atomic radius.
Metallic Character: Decreases. The increase in effective nuclear charge across a period makes it harder for atoms to lose their valence electrons. Hence, the tendency to lose electrons decreases, leading to a decrease in metallic character.

18 groups7 periodsatomic size increasesmetallic character increasesatomic size decreasesmetallic character decreasesnuclear chargevalence shells

Marking Scheme

1State that there are 18 groups and 7 periods in the Modern Periodic Table. (1 mark)
2Explain that down a group, atomic size increases (due to addition of shells) and metallic character increases (due to decrease in nuclear pull on valence electrons). (1 mark)
3Explain that across a period (left to right), atomic size decreases (due to increased nuclear charge pulling electrons closer) and metallic character decreases (due to increased difficulty in losing electrons). (1 mark)

Hint

Recall the number of vertical columns and horizontal rows in the periodic table. Think about how nuclear charge and the number of shells change down a group and across a period, and how this affects the ease of losing electrons.

Quick Oral Answer

Q: Why does metallic character increase down a group? A: Down a group, atomic size increases because new shells are added. This decreases the nuclear attraction on valence electrons, making it easier for the atom to lose electrons and exhibit metallic character.

Analysis & Explanation

The Modern Periodic Table organizes elements by increasing atomic number. The trends in physical and chemical properties are governed by electronic configurations:

Atomic Size (Radius): Determined by the distance between the nucleus and the outermost shell. Down a group, shell addition dominates, increasing size. Across a period, increasing nuclear charge pulls the same shell closer, decreasing size.
Metallic Character: Metals tend to lose electrons to form cations (electropositive nature). This tendency is directly proportional to atomic size and inversely proportional to nuclear pull. Thus, metallic character increases down a group (easier to lose electrons) and decreases across a period (harder to lose electrons).

Common Mistakes

1Confusing groups with periods (e.g., writing 7 groups and 18 periods).
2Stating that atomic size decreases down a group due to increasing nuclear charge, forgetting that new shells are added.
3Confusing metallic character with non-metallic character trends.

Interesting Facts

Francium, located at the bottom-left of the periodic table, is theoretically the most metallic and reactive element, but it is highly radioactive and unstable.

Helium has the smallest atomic radius of all elements, even smaller than Hydrogen, due to its higher nuclear charge pulling its two electrons closer.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2015?

This question carries 3 marks in the CBSE Class 10 Science 2015 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 "Metallic Character and Periodic Trends" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2015 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2015 paper.