What is periodicity in properties of elements with reference to the Modern Periodic Table? Why do all the elements of the same group have similar properties? How does the tendency of elements to gain electrons change as we move from left to right in a period? State the reason of this change.
What is periodicity in properties of elements with reference to the Modern Periodic Table? Why do all the elements of the same group have similar properties? How does the tendency of elements to gain electrons change as we move from left to right in a period? State the reason of this change.
- Periodicity: Periodicity in properties refers to the regular recurrence of similar physical and chemical properties of elements after certain regular intervals when they are arranged in the order of their increasing atomic numbers in the Modern Periodic Table.
- Reason for similar properties in a group: All elements belonging to the same group have the same number of valence electrons (outermost shell configuration). Since the chemical behavior of an element is determined by its valence electrons, elements in the same group exhibit highly similar chemical properties.
- Tendency to gain electrons in a period: The tendency of elements to gain electrons increases as we move from left to right across a period.
- Reason for this change: As we move from left to right in a period, the atomic number increases, which increases the nuclear charge (number of protons in the nucleus). Meanwhile, the electrons are added to the same valence shell, meaning the shielding effect remains relatively constant. This results in an increase in the effective nuclear charge, which exerts a stronger attractive force on incoming electrons, making it easier for the atom to gain electrons.
Marking Scheme
- 11 Mark: Correct definition of periodicity.
- 21 Mark: Explanation of group similarity based on valence electrons.
- 31 Mark: Correct trend (increases) and explanation based on increasing effective nuclear charge.
Hint
Think about how the atomic size and nuclear charge change as you move from left to right in a period, and how this affects the pull on an incoming electron.
Quick Oral Answer
Periodicity is the repetition of properties at regular intervals. Elements in the same group have similar properties because they have the same number of valence electrons. Across a period, the tendency to gain electrons increases due to an increase in effective nuclear charge.
Analysis & Explanation
This question tests the fundamental understanding of periodic trends. Periodicity arises due to the recurrence of similar valence shell electronic configurations. Across a period, the atomic size decreases and the nuclear pull increases, which directly enhances the tendency of elements to gain electrons to complete their octet (non-metallic character increases). In contrast, down a group, the atomic size increases, making it harder to gain electrons.
Common Mistakes
- 1Stating that the number of shells increases across a period.
- 2Confusing the tendency to gain electrons (non-metallic character) with the tendency to lose electrons (metallic character).
Interesting Facts
Dmitri Mendeleev left gaps in his periodic table for undiscovered elements, predicting their properties with astonishing accuracy based on periodicity, long before the Modern Periodic Table was established.
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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 "Periodicity and Chemical Properties" 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.