Write the quantum numbers for the 4th and 8th electron of Oxygen (O) atom.
Arrange each set in order of decreasing atomic size:
(a) Cl, K, S
(b) Mg, K, Ca
(c) F, Ne, Na
(d) Be, Mg, Na
and arrange each set of atoms in order of decreasing IE1:
(a) Na, Li, K
(b) Be, F, C
(c) Cl, Ar, Na
(d) Cl, Br, Se
The Correct Answer and Explanation is:
Let’s tackle the questions in two parts:
1. Write the quantum numbers for the 4th and 8th electron of Oxygen (O) atom.
Oxygen (Atomic number 8):
Electron configuration: 1s² 2s² 2p⁴
- 4th electron:
This electron goes into the 2s subshell.- n (principal quantum number): 2 (second shell)
- l (azimuthal/angular momentum): 0 (s-orbital)
- ml (magnetic quantum number): 0 (only one value for l = 0)
- ms (spin quantum number): –½ (since it’s the second electron in 2s, it pairs with the first)
2. Arrange each set in order of decreasing atomic size and decreasing first ionization energy (IE₁):
Atomic Size:
First Ionization Energy (IE₁):
IE₁ is the energy needed to remove an electron from a gaseous atom. It increases across a period and decreases down a group
Conclusion:
Understanding quantum numbers helps determine an electron’s position and spin in an atom. The periodic trends in atomic size and ionization energy reflect the atomic structure and nuclear charge. Atomic size increases down a group and decreases across a period. Ionization energy follows the opposite trend because electrons are more tightly bound in smaller atoms with higher nuclear charge. This knowledge is essential in predicting chemical behavior and reactivity of elements.