Atoms and molecules

Question

Question 1:

a) Compute the radius of the second and third orbits in He+ ion. As well compute the energy of the electron in the second and third orbits of He⁺ ion.

b) Compute the wave number (m^-1) and energy (kJ mol)^-1 of the light of wavelength 800 nm.

Question 2:

a) Write down the values of four quantum numbers for 4s and 4p electrons.

b) Compute the de Broglie wavelength related with a body of mass 1.5 kg moving with a velocity of 100 m s^-1

Question 3:

a) Arrive at the Lewis structures of ICI⁺₂ and ICI^-₂ ions. By using VSEPR theory, predict the shapes of such compounds.

b) Compute the bond lengths in bromoethane and bromoethylene by using covalent radii values. For hydrogen, suppose that the covalent radius in 28 pm in such compounds.

Question 4:

a) Describe the structure of BF3 molecule based on hybridization concept. What is its shape?

b) Starting from Lewis structures, find out the hybridization type of the central atoms in IF⁺₄ and ICI⁻₄.

Question 5:

a) State the definitions of bonding, antibonding and nonbonding orbital. Draw the molecular orbital obtained by the linear combination of two 1s orbital.

b) By using the molecular orbital theory, describe why the oxygen-to-oxygen bond is stronger in oxygen molecule than in peroxide (O₂^2-) ion.

Question 6:

a) The element X forms a compound, XOCl₃, in which X and O form a double bond while the X and Cl form single bonds. Recognize X from the given elements:

i) Al ii) Si iii) P (iv) S.

Give reason for your answer. Predict the shape of the molecule.

b) You are given a gaseous substance. Recommend an experimental method to determine whether it is polar or nonpolar. Describe the steps to be used in this method.

Question 7:

a) The bond length of Hl molecule is 163 pm. Compute its:

i) Moment of inertia and
ii) Rotational constant.

b) What is the essential condition for a molecule to be microwave active? Give three illustrations each for the diatomic molecules.

i) Having microwave activity and
ii) Not having microwave activity.

Question 8:

a) Calculate the ratio fo the fundamental frequencies of Hl and Dl.

b) Based on Beer-Lambert law, describe the method of finding out the concentration of a given solution of potassium dichromate. You are as well provided with a standard solution of potassium dichromate.

Question 9:

a) The rate constant for the radioactive disintegration of ⁶⁰₂₇Co is 0.1317 year^-1. Compute the mass of ⁶⁰₂₇Co that will remain after 21.04 years out of 1 gram sample.

b) Describe the principle of finding out the age of organic materials by using radioactive dating method.