Ques. 1NEET 2013
Based on equation E = -2.178 10-18 J ( Z2n2 ), certain conclusions are written. Which of them is not correct ?
- Equation can be used to calculate the change in energy when the electron changes orbit.
- For n = 1, the electron has a more negative energy than it does for n = 6 which means that the electron is more loosely bound in the smallest allowed orbit.
- The negative sign in equation simply means that the energy of electron bound to the nucleus is lower than it would be if the electrons were at the infinite distance from the nucleus.
- Larger the value of n, the larger is the orbit radius.
Answer
(2) For n = 1, the electron has a more negative energy than it does for n = 6 which means that the electron is more loosely bound in the smallest allowed orbit.
Solution
(1) Correct: E = Ef - Ei can be found from the equation for any two orbits.
(2) Not correct: for n = 1 the energy is the most negative, so the electron is most tightly (not loosely) bound in the smallest allowed orbit.
(3) Correct: as per NCERT, the negative sign means the energy of the bound electron is lower than that of a free electron at infinite distance (E = 0).
(4) Correct: rn = 52.9 n2Z pm ⇒ radius increases with n.
Answer: (2)