2 marksShort AnswerSection A

In the modern periodic table, the element Calcium (atomic number = 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these elements has physical and chemical properties resembling those of Calcium and why ?

Q: In the modern periodic table, the element Calcium (atomic number = 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these elements has physical and chemical properties resembling those of Calcium and why ?

The elements with atomic numbers **12** and **38** have physical and chemical properties resembling those of Calcium ($Z=20$). **Reason:** Chemical properties of an element are determined by its electronic configuration, specifically the number of valence electrons. - Calcium ($Z=20$) has the electronic configuration: $2, 8, 8, 2$. It has **2** valence electrons. - Element with $Z=12$ (Magnesium) has the configuration: $2, 8, 2$. It has **2** valence electrons. - Element with $Z=38$ (Strontium) has the configuration: $2, 8, 18, 8, 2$. It has **2** valence electrons. Since elements $12$, $20$, and $38$ all have the same number of valence electrons, they belong to the same group (Group 2) and exhibit similar chemical properties.

Chemical Reactions and Equations

Chemical Properties and Electronic Configuration

Official Answer

The elements with atomic numbers 12 and 38 have physical and chemical properties resembling those of Calcium ( $Z=20$ ).

Reason:

Chemical properties of an element are determined by its electronic configuration, specifically the number of valence electrons.

Calcium ( $Z=20$ ) has the electronic configuration: $2, 8, 8, 2$ . It has 2 valence electrons.
Element with $Z=12$ (Magnesium) has the configuration: $2, 8, 2$ . It has 2 valence electrons.
Element with $Z=38$ (Strontium) has the configuration: $2, 8, 18, 8, 2$ . It has 2 valence electrons.

Since elements $12$ , $20$ , and $38$ all have the same number of valence electrons, they belong to the same group (Group 2) and exhibit similar chemical properties.

Electronic configurationValence electronsSame groupChemical propertiesAtomic number

Marking Scheme

1Identification of elements with atomic numbers 12 and 38. (1 mark)
2Explanation based on same number of valence electrons (2). (1 mark)

Hint

Write the electronic configuration for each atomic number and find which ones have the same number of electrons in the outermost shell as Calcium ( $Z=20$ ).

Quick Oral Answer

Elements 12 and 38 resemble Calcium because they all have 2 valence electrons. This puts them in the same group of the periodic table, giving them similar reactivity.

Analysis & Explanation

The text mentions that chemical reactions involve the 'breaking and making of bonds between atoms'. The ability to form bonds is dictated by valence electrons. Calcium ( $Ca$ ) reacts with oxygen to form $CaO$ (as seen in the text's logic for $MgO$ ). Elements in the same group have the same valency and thus form similar compounds (e.g., $MgCl_2$ , $CaCl_2$ , $SrCl_2$ ). Atomic numbers $19$ (Potassium) and $21$ (Scandium) have $1$ and $3$ valence electrons respectively, so they do not resemble Calcium.

Common Mistakes

1Choosing 19 or 21 because they are numerically close to 20.
2Failing to provide the electronic configuration as part of the reasoning.

Interesting Facts

Calcium, Magnesium, and Strontium are all 'Alkaline Earth Metals'. They are all found in the Earth's crust and are quite reactive, never found free in nature.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2011?

This question carries 2 marks in the CBSE Class 10 Science 2011 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Chemical Reactions and Equations" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Chemical Properties and Electronic Configuration" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2011 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2011 paper.