# Oxygen Atom

Oxygen accounts for about 23% of the atmosphere's mass with pairs of oxygen atoms stuck together to make dioxygen molecules, but it's not just in the air, we breathe. Overall, it's the most abundant element on the earth's surface and the third most abundant in the universe after hydrogen and helium. Oxygen is a colorless, odorless and tasteless gas. It will support life. It is noncombustible, but will actively support the burning of combustible materials.

### An oxygen atom has a total of 8 elections. How do you write the 4 quantum numbers for each of the 8 electrons in the ground state ?

You know that a neutral oxygen atom has 8 electrons.

It's always helpful to write the electron configuration for an element before trying to assign quantum numbers for each individual electron . As you can see in the image above, the electron configuration for neutral oxygen is

$' O ' : 1 {s}^{2} 2 {s}^{2} 2 {p}^{4}$

Assuming you know the basics behind quantum numbers, you can write the unique 4-number set for each electron belonging to oxygen like this

The first energy level:

$' n = 1 '$, $' l = 0 '$, $' m {'}_{l} ' = 0 '$, $' m {'}_{s} ' = - \frac{1}{2} '$$\to$ the electron located in the 1s-orbital, spin-down;
$' n = 1 '$, $' l = 0 '$, $' m {'}_{l} ' = 0 '$, $' m {'}_{s} ' = + \frac{1}{2} '$$\to$ the electron located in the 1s-orbital, spin-up;

The second energy level:

$' n = 2 '$, $' l = 0 '$, $' m {'}_{l} ' = 0 '$, $' m {'}_{s} ' = - \frac{1}{2} '$$\to$ the electron lcoated in the 2s-orbital, spin-down;
$' n = 2 '$, $' l = 0 '$, $' m {'}_{l} ' = 0 '$, $' m {'}_{s} ' = + \frac{1}{2} '$$\to$ the electron located in the 2s-orbital, spind-up;

$' n = 2 '$, $' l = 1 '$, $' m {'}_{l} ' = - 1 '$, $' m {'}_{s} ' = - \frac{1}{2} '$$\to$ the electron located in the $' 2 p {'}_{x} ' - \mathmr{and} b i t a l '$, spin-down;
$' n = 2 '$, $' l = 1 '$, $' m {'}_{l} ' = - 1 '$, $' m {'}_{s} ' = + \frac{1}{2} '$$\to$ the electron located in the $' 2 p {'}_{x} ' - \mathmr{and} b i t a l '$, spin-up;
$' n = 2 '$, $' l = 1 '$, $' m {'}_{l} ' = 0 '$, $' m {'}_{s} ' = + \frac{1}{2} '$$\to$ the electron located in the $' 2 p {'}_{y} ' - \mathmr{and} b i t a l '$, spin-up;
$' n = 2 '$, $' l = 1 '$, $' m {'}_{l} ' = 1 '$, $' m {'}_{s} ' = + \frac{1}{2} '$$\to$ the electron located in the $' 2 p {'}_{z} ' - \mathmr{and} b i t a l '$, spin-up;

First, you must know the rules for quantum numbers.

## Oxygen Atoms

#### Explanation:

Then you use the Aufbau Principle, the Pauli Exclusion Principle, and Hund's Rule to assign the quantum numbers.

The rules for quantum numbers are:

#n = 1, 2, 3… ∞#.
#l = 0, 1, 2… n – 1#
#m_l = -l… -1, 0, 1… l#
#m_s = ±1/2#

No two electrons can have the same set of four quantum numbers.

According to the Aufbau Principle, electrons fill orbitals starting at the lowest possible energy levels.

So the first two electrons have the quantum numbers

$\left.\begin{matrix}\boldsymbol{n} & \boldsymbol{l} & {\boldsymbol{m}}_{l} & {\boldsymbol{m}}_{s} \\ 1 & 0 & \textcolor{w h i t e}{i} 0 & + \frac{1}{2} \\ 1 & 0 & \textcolor{w h i t e}{i} 0 & - \frac{1}{2}\end{matrix}\right.$

The Pauli Exclusion Principle states that no two electrons in the same atom can have the same set of four quantum numbers.

So the next two electrons have the quantum numbers

$\left.\begin{matrix}\boldsymbol{n} & \boldsymbol{l} & {\boldsymbol{m}}_{l} & {\boldsymbol{m}}_{s} \\ 2 & 0 & \textcolor{w h i t e}{i} 0 & + \frac{1}{2} \\ 2 & 0 & \textcolor{w h i t e}{i} 0 & - \frac{1}{2}\end{matrix}\right.$

Now Hund's Rule comes into effect.

Hund's Rule states that if two or more orbitals of equal energy are available, electrons will occupy them singly and with the same spin before filling them in pairs.

The next four electrons have the quantum numbers

$\left.\begin{matrix}\boldsymbol{n} & \boldsymbol{l} & {\boldsymbol{m}}_{l} & {\boldsymbol{m}}_{s} \\ 2 & 1 & - 1 & + \frac{1}{2} \\ 2 & 1 & \textcolor{w h i t e}{X} 0 & + \frac{1}{2} \\ 2 & 1 & + 1 & + \frac{1}{2} \\ 2 & 1 & - 1 & - \frac{1}{2}\end{matrix}\right.$

And now you have the quantum numbers for the eight electrons in an oxygen atom.

## Related questions

In his well-known poem 'The Rime of the Ancient Mariner', Samuel Coleridge wrote 'Water, water everywhere, Nor any drop to drink'. The narrator was talking about being out on the ocean, but not having any water because he had killed an albatross (apparently bringing bad luck to everyone on the ship). About (75%) of the Earth's surface is water. The major constituent of the human body (over (60%)) is water. This simple molecule plays important roles in all kinds of processes.

## Structure of Water

Water is a simple molecule consisting of one oxygen atom bonded to two different hydrogen atoms. Because of the higher electronegativity of the oxygen atom, the bonds are polar covalent (polar bonds). The oxygen atom attracts the shared electrons of the covalent bonds to a significantly greater extent than the hydrogen atoms. As a result, the oxygen atom requires a partial negative charge (left( delta - right)), while the hydrogen atoms each acquire a partial positive charge (left( delta + right)). The molecule adopts a bent structure because of the two lone pairs of electrons on the oxygen atom. The (ce{H-O-H}) bond angle is about (105^text{o}), slightly smaller than the ideal (109.5^text{o}) of an (sp^3) hybridized atomic orbital.

The bent shape of the water molecule is critical because the polar (ce{O-H}) bonds do not cancel one another and the molecule as a whole is polar. The figure below illustrates the net polarity of the water molecule. The oxygen is the negative end of the molecule, while the area between the hydrogen atoms is the positive end of the molecule.

Polar molecules attract one another by dipole-dipole forces as the positive end of one molecule is attracted to the negative end of the nearby molecule. In the case of water, the highly polar (ce{O-H}) bonds results in very little electron density around the hydrogen atoms. Each hydrogen atom is strongly attracted to the lone-pair electrons on an adjacent oxygen atom. These are called hydrogen bonds and are stronger than conventional dipole-dipole forces.

Because each oxygen atom has two lone pairs, it can make hydrogen bonds to the hydrogen atoms of two separate other molecules. The figure below shows the result - an approximately tetrahedral geometry around each oxygen atom consisting of two covalent bonds and two hydrogen bonds.

## Summary

• Water is a molecular compound consisting of polar molecules that have a bent shape.
• The oxygen atom acquires a partial negative charge while the hydrogen atom acquires a partial positive charge.