Session 3, Periodic properties, 2022 Arvind Sir Luv Sir Suri Sir Theory Class: Theory Class: Theory Class: Monday Tuesday & Thursday Wednesday & Saturday & Friday (7pm) (7pm) (7pm) MCQ Class: Tuesday MCQ Class: Saturday MCQ Class: Friday (8pm) (8pm) (8pm) Daily Schedule Join Vedantu JEE Telegram channel NOW! Assignments Notes Daily Update https://vdnt.in/JEEVedantu Quick Recap: ● Modern Periodic Table ● Prediction of group number, block and period of an element. Learning objectives: Atomic radius and variation of atomic radius across the periodic table Atomic radius Covalent Radius So covalent radius for A-A rA = dA-A /2 If covalent bond is formed between two different elements then χ χ dA-B = rA + rB + 0.09( A - B) χ χ Where A - B are electronegativities of A and B Atomic radius So van der waals radius for A-A rA = dA-A /2 Van Der Waals Radius Atomic radius Metallic Radius (Crystal radius) So metallic radius for A-A rA = d/2 Note: rcovalent < rmetallic < rvan der waals Variation of Atomic Radii in the Periodic Table The covalent radii, van der Waals radii and ionic radii decrease with increase in atomic number as we move from left to right in a period due to the increase in ENC. Variation along a group Atomic radius in a group increase as the atomic number increases. It is because within the group, the principal quantum number (n) increases Anion with the greater negative charge Isoelectronic Species will have the larger radius. In this case, the net repulsion of the electrons will Order of atomic radii is outweigh the nuclear charge and the ion 2+ + – 2– Mg < Na < F < O will expand in size. Summary: Check your Knowledge: Atomic radii of fluorine and neon in Angstrom units are respectively given by: a. 0.72, 1.60 b. 1.60, 1.60 c. 0.72, 0.72 d. None of these Check your Knowledge: Atomic radii of fluorine and neon in Angstrom units are respectively given by: a. 0.72, 1.60 b. 1.60, 1.60 c. 0.72, 0.72 d. None of these Solution: The reported radii of noble gas elements are "van der Waals radii", which are 40% more than the actual atomic radii. Hence neon's atomic radius must be much more than that of fluorine. Note: It is not possible to get covalent and metallic radii for noble gases since they do not form bonds. Hence the correct option is (a) Check your Knowledge: Which of the following is the smallest in size? 1. N3- 2. O2- 3. F- 4. Na+ Check your Knowledge: Which of the following is the smallest in size? 1. N3- 2. O2- 3. F- 4. Na+ Solution: In today’s session we learnt: Types of atomic radius Variation of atomic radius across a periodic table. Next session: Periodic properties of elements .