- When you talk about any molecule, you try to find out the main features of its structure. Which atom is more electronegative? How are atoms arranged in it? Juggling with these many questions makes you more interested in finding out them.
Hydrogen sulfide is a colorless molecule with a chemical formula H2S. It is poisonous and has a foul odor like a rotten egg.
So, is H2S polar or nonpolar? H2S is a slightly polar molecule because of its bent shaped geometrical structure and the small difference between the electronegativity of Hydrogen(2.2) and Sulfur(2.58) that results in a non zero dipole moment.
Other properties of H2S are:
- It easily reacts with metal ions to result in metal sulfides.
- It is dangerous and toxic, especially for oxygen inhalers.
- Being a corrosive, it destructs metals like copper turning into green in color after the reaction.
It was discovered in the year 177 by a chemist named Carl Wilhelm Scheele. This gas is produced by human bodies and we uses it as a signaling molecule.
What do you mean by polarity?
Polarity is described as how electrons are distributed in the molecule. It shows wherewith electrons are attracted and pulled by the most electronegative atom.
But, how do you assess the polarity of the element? Let’s find it out by learning little information about the concept of electronegativity as it does matter to polarity.
Electronegativity represents the ability of elements to attract electrons. Thus elements that attract more electrons will be more electronegative.
Electronegativity determines the distribution of electrons to find the polarity of a molecule.
What is a polar molecule?
Since a molecule is neutral but it is called as polarised when one side is more negative charge than the other positive-charged side.
It has an asymmetrical arrangement of atoms, while there is an uneven distribution of negative charges (electrons) outside the central atom.
Water (H2O) is a polar molecule because the more electronegative Oxygen has a higher concentration of electrons than the other atom of the molecule i.e. Hydrogen is positively charged.
You can check out the reason for the polarity of H2O.
Other molecules like SO2, NH3, etc. are also polar molecules.
For nonpolar molecules like CO2, you can check out the reason for the non-polarity of CO2.
How can you differentiate between polar and non-polar molecules?
The polar molecules have an unequal sharing of electrons i.e. the charges are not balanced. But in non-polar molecules, there are relatively equal numbers of electrons.
You know oxygen (O=O) is very electronegative but, yet, it is non-polar. Why?
Both atoms in the molecule O2 have an equal density of electronegativity, meaning they share an equal number of electrons. Hence, the molecule O2 is non-polar. Molecules that consist of the same type of elements like H2, N2, Cl2, etc. are known as dipoles.
By default, they are non-polar molecules. Hydrocarbons like methane (CH4), ethane (C2H6), etc. containing elements hydrogen and carbons are also termed as non-polar molecules.
How to test the polarity of H2S?
Before you jump to find out the polarity of the molecule, H2S, let’s talk about its bond polarity. The polarity of a bond is calculated when the atoms of a molecule have partial positive and negative charges.
Importance of Electronegativity
If the difference between the electronegativities of the two elements is greater or equal to 0.5, then the bond is polar.
With atomic number 16, Sulfur pulls both the electrons of Hydrogen to complete its last shell and gains a negative charge.
Hydrogen becomes positive-charged. Hence, the electronegativity of Sulfur becomes higher than that of the Hydrogen atom.
As you know, in the periodic table, electronegativity increases from left to right and decreases from top to down.
The electronegativity of Hydrogen and Sulfur is 2.20 and 2.58, respectively. Their electronegativity difference, 0.38, is less than 0.5. Thus, H2S is a non-polar bond.
Due to Sulfur being more electronegative than Hydrogen, it is partially negative. As a result, it creates a dipole moment.
Furthermore, the dipole moment is portrayed by an arrow pointing to a more electronegative atom. In the case of the H2S compound, the dipole moment is represented from Hydrogen (delta +) to Sulfur (delta-).
Importance of Geometrical shape
To determine the polarity of any molecule like H2S, it is equally important to find out its outside atoms, and shape.
There are two lone pairs of electrons on the central atom Sulfur that causes the H-S bond to be in a bent shape. Hence, the molecule has an odd distribution of atoms around the central atom making it non-symmetrical.
Because of its bent shape, the dipole moment is created between the H-S bonds. The greater the separation of charges more is the dipole moment between the atoms. Hence, Sulfur attracts more electrons and gains a partial negative charge.
Hydrogen is a partial positive charge as it is now left with fewer positive charges.
Since the dipole moment has a direction and magnitude, it is a vector quantity. It directs towards more electronegative atom.
When the arrows do not cancel out each other, the molecule becomes polar.
Importance of Dipole Moment
The factor dipole of a molecule shows the level of its polarity. Greater the polarity of a molecule more is the value of its dipole moment.
It can be also be defined as the product of charges of two atoms and the distance between them.
D = Q * R
D = dipole moment
Q = charge on atoms
R = distance between them
Uses of H2S
- It is used to produce hydrogen and sulfuric acid.
- It is widely used industrially to produce different varieties of inorganic compounds.
- It is used for manufacturing pesticides for crops on a larger scale.
- Hydrogen sulfide has its great use as heavy water used in nuclear power plants.
To calculate the polarity of any molecule, certain factors need to be considered before you reach out to a conclusion.
- How does bond polarity affect the polarity of a molecule?
- How to determine the direction of a molecule’s polarity?
- Does the shape affect polarity?
- How do symmetrical and asymmetrical help to find out the polarity of a molecule?
H2S is the polar molecule with Hydrogen atoms bonded outside the central Sulfur atom. It has an asymmetrical bent shape that creates a dipole moment between atoms.
Sulfur is more electronegative than Hydrogen. This refers to Sulfur has more electrons than the latter one.
As you know the electronegative difference of the molecule H2S is 0.4, which is considered to be negligible and has weak polarity too.
Technically, due to the absence of enough polarity between the atoms, the H2S is said to be a non-polar molecule.
This is an exceptional case that needs to be counted. According to certain studies, for a molecule to be polar, the electronegativity has to be between 0.5 and 2.
Q1. Name the compounds that have a polar bond.
A1. The compounds that have polar bonds are Water (H2O), Ammonia (MH3), and Sulfur Dioxide (SO2).
Q2. What is a dipole moment? How do you calculate its magnitude?
A2. A dipole moment is represented by a specialized arrow pointed out from a partially positive end to the partially negative side.
In the case of molecules having more than two atoms, there are two possibilities to occur-
a) When the dipole moment is canceled out i.e. when the arrows are in the opposite direction its magnitude is equal to zero. The molecule is non-polar.
b) The arrows between the central atom and the other atoms are pointing either away from or towards the central atom. In such a case, the magnitude of the dipole moment is more than zero making it a polar molecule.
Q3. Write down the electronegativities of elements.
A3. Oxygen- 3.44
Q4. Calculate the electronegativity difference between molecules of CH4 and CO2.
A4. a) CH4
Carbon- 2.55, Hydrogen- 2.20
The electronegative difference is-
CH4 is a non-polar molecular because the dipole moment between atoms cancels out each other.
Sulfur- 2.58, Oxygen- 3.44
The electronegative difference is-
3.44- 2.58= 0.86
CO2 is a polar molecule because the dipole moment between atoms does no cancel each other, and the magnitude is greater than 0.