# Ionization Energy

1. Oct 10, 2005

### erik05

Hello everybody, just wondering if anyone could point me in the right direction for this question. Please and thanks.

1) Since the ionisation process takes an electron from its ground state to the zero level of the energy scale, the ground state energy calculated for the electron of the hydrogen atom can be compared to the negative of its ionization energy (IE). Use the equation E= -2.178 x 10^-18 (Z^2/n^2) for energy of a valence level n, to build a equation that can be used to calculate the ionisation energy of H in units of kJ/mol.

So far what I have is....

Since Z represents the atomic number and the atomic number for hydrogen is 1:

E= -2.178 x 10^-18 (1^2/n^2)

so equation is E= -2.178 x 10^-18 (1/n^2)

2) Use equation to calculate ionization IE for H and confirm that value obtained is consistent with the experimental value of 1310 kJ/mol.

E= -2.178 x 10^-18 (1/ (1-0)^2) since electron going from ground state to zero level therefore:
E= -2.178 x 10^-18 J per 1 atom. So then,

E= -2.178 x 10^-18 J/atom x (6.022 x 10^23 atom/mol) / 1000
= -1312 kJ/mol

2. Oct 12, 2005

### Gokul43201

Staff Emeritus
Your answer is correct, but there is a tiny error in the way you've substituted in the formula.

Where did you get 1/(1-0)^2 from ? The ionization energy is the energy difference between the first shell and an infinitely removed shell. So the shell dependence goes like $1/n_1^2 - 1/n_2^2 = 1/1^2 - 1/\infty^2 = 1 - 0 = 1$. The rest is good.

PS : Didn't I answer an almost identical question recently ?

EDIT : Found it : https://www.physicsforums.com/showthread.php?t=93440