Question

2. (40 pts) Provide short answers for the following questions. 1) List ionic compounds KBr, CaO, KCl, and Sro: in order of increasing magnitude of lattice energy: in order of decreasing melting point: 2) The first four ionization energies for the elements X and Y are shown in a table below. Predict the elements X and Y. There may be more than one correct answer, so explain completely. The units are not kJ/mol. IE 170 200 IE2 350 400 IE: 1800 3500 IE2500 5000 3) The principal quantum number determines In hydrogen, the orbital energy depends upon quantum number(s). In multielectron atoms, the orbital energy depends upon quantum number(s) 4) The wavelength of the light when hydrogen electron relaxes from n=5 to n=2 is 434nm (violet). A student predicted that hydrogen electron transitions from n=5 to n=3 would emit light in the ultraviolet region. Is this prediction correct? Explain. 5) The ground state electron configurations of three atoms are: A =[Ar]4s23d104p!, B =[Ar]4s%3d104p4, C = [Ar]4s%3d104ps. Arrange atoms A, B, and C in order of decreasing first ionization energy: in order of increasing atomic radius:

Answer 1

1. Lattice energy depends upon charge and the ionic radius of ionic compound.

Lattice energy is directly proportional to Charge and inversely proportional to ionic radius

While comparing we will first look for Charge.

so the order is :

CaO > SrO > KCl > KBr

Melting point of Ionic compound also depends on charge and ionic radius in the sane way.

so Higher the lattice energy higher the melting point.

So melting point order is:

CaO> SrO > KCl > KBr

2. X can be Calcium atom

and Y can be Magnesium atom

Both X and Y have very high 3rd Ionization energy which means ejection of 2rd electron attend a Nobel gas configuration and ejecting 3rd electron is tougher.

Also Y has more IE than X it means Y has smaller atomic radius than X

3. Principal quantum number determines the shell of electrons

In hydrogen atom, the orbital energy depends upon the principal quantum number only.

Whereas in multi-electron orbital energy depends upon both principal quantum number and Azimuthal quantum number.

4. Students prediction is wrong because electron transition from n=5 to n= 3 cause less energy emission than the electron transition from n= 5 to n=2.

So in n=5 to n=3 will have larger wavelength than violet.

Note: ultraviolet have shorter wavelength than violet and ultraviolet have more energy than violet.

5. 1st ionization energy order is :

C > A > B

Atomic radius order is:

A>B > C