Answer to Question #63651 in General Chemistry for Emmanuel D. Kollie

Question

Discuss the following: 1) Aufbau Principle 2) Hund's Rule 3) Paull Exclusion Principle 4) Oribital Notation 5) Electron dot Notation 6) Isotope and Isobar 7) Allotrope and Alloy

Answer 1

1) The equations of modern atomic theory are difficult to solve. Fortunately, many of the results can be obatined by following some simple rules. These rules are known as the Aufbau principle.
2) Hund's rule states that:
a) Every orbital in a sublevel is singly occupied before any orbital is doubly occupied.
b) All of the electrons in singly occupied orbitals have the same spin (to maximize total spin).
3) No two electrons in an atom can have identical quantum numbers. This is an example of a general principle which applies not only to electrons but also to other particles of half-integer spin (fermions). It does not apply to particles of integer spin (bosons).
4) Orbital notation is simply a different means that chemists use to describe the wavefunction for a hydrogen atom. Rather than using the term wavefunction, instead we use the word "orbital".
The orbital notation uses only the n and ℓ quantum numbers.
In this notation we simply state the principle quantum number n as a number. A letter is used to denote the ℓ term as letters s,p,d...
So let's imagine a hydrogen atom in its lowest energy state. This is the ground state. The electron wavefunction is then described by n=1, ℓ = 0, and mℓ=0. We could also simply call this "orbital" a 1s orbital. (note: when doing this we ignore any mention of mℓ. We might use light to excite the hydrogen atom to a higher energy state. Let's say we went from 1s to 2p. The excited state could then have quantum numbers n=2, ℓ =1. In the absence of any external perturbations such as a magnetic field all the mℓ levels are the same. So any mℓ solution could describe this state.
5) Electron Dot Structures - Helpful tools in thinking about bonding.
Pictorial representation of the valence electron configuration around an atom.
6) Atoms of the same element can be different. These different atoms of the same element are called isotopes. Isobars are atoms of different elements with the same mass number but their atomic numbers are different.
7) Allotropes are different forms of the same element. Different bonding arrangements between atoms result in different structures with different chemical and physical properties.
An alloy is a mixture of metals or a mixture of a metal and another element.