Question

Hydrogen bond between two atoms is formed due to (a) displacement of electrons towards more electronegative atom resulting in fractional positive charge on hydrogen (b) displacement of electrons towards hydrogen atom resulting in a polar molecule (c) formation of a bond between hydrogen atoms of one molecule and the other (d) existence of an attractive force which binds hydrogen atoms together.

Short answer

Hydrogen bonding is formed due to the displacement of electrons towards a more electronegative atom, resulting in a partial positive charge on hydrogen, making option (a) correct.

Step-by-step solution

Understand the Concept of Hydrogen Bonding

Hydrogen bonding is an intermolecular force that occurs when a hydrogen atom that is bonded to a highly electronegative atom (such as oxygen, nitrogen, or fluorine) experiences an attraction to another electronegative atom. In this attraction, the hydrogen atom carries a partial positive charge because its electron density is pulled towards the more electronegative atom it is bonded to.

Evaluate the Given Options

Now, look at each option given in the question and check which one correctly describes hydrogen bonding: Option (a) mentions displacement of electrons towards a more electronegative atom and a partial positive charge on hydrogen. Option (b) incorrectly implies that electrons move towards hydrogen. Option (c) mixes the concept of intermolecular bonding with the formation of a bond between hydrogen atoms, which is not characteristic of hydrogen bonding. Option (d) is too vague and does not exactly describe the nature of hydrogen bonding.

Identify the Correct Option

Comparing the options with the concept of hydrogen bonding, option (a) is the one that correctly explains that hydrogen bonding involves the displacement of electron density towards a more electronegative atom, leaving hydrogen with a fractional positive charge and allowing it to form a bond with another electronegative atom. Hence, the answer is (a).

Key concepts

Intermolecular Forces

Imagine holding hands with someone—this connection is similar to what we call intermolecular forces, which are the forces of attraction or repulsion that act between neighboring particles, such as atoms, molecules, or ions. They hold substances together and come in various types, including hydrogen bonds, dipole-dipole interactions, London dispersion forces, and ion-dipole forces.

Hydrogen bonds are a unique type of intermolecular attraction—they're stronger than most but weaker than covalent or ionic bonds that hold compounds together. These special bonds are the reason why water has such a high boiling point compared to other molecules of a similar size, and why ice floats on water. Think of it as a 'super' hand-holding moment that makes remarkable things happen in molecular chemistry!

Electronegativity

Now let's get into electronegativity. Picture a tug of war where electrons are the rope. Electronegativity is essentially how strongly an atom can 'pull' on electrons in a bond. It's a measure of the atom's ability to attract and hold on to these tiny, negatively charged particles.

On the periodic table, fluorine is the ultimate champion of this tug of war—it's the most electronegative element. Oxygen, nitrogen, and chlorine are also quite good at pulling electrons towards them. When an atom like hydrogen bonds with these electron-hogging elements, it sets the stage for hydrogen bonding because the electrons get pulled away from the hydrogen, giving it a sort of 'electron loneliness' which is crucial for the formation of hydrogen bonds.

Partial Positive Charge

When the electrons are pulled in a bond toward the more electronegative atom, the less electronegative partner, like hydrogen, ends up with a deficit—it's like if someone were to keep your wallet a bit longer after borrowing money, leaving you with less cash at hand. This imbalance creates what we call a partial positive charge (+) on hydrogen. It's not a full charge like on ions, but it's enough for hydrogen to start seeking a new electron buddy—setting its sights on the nearby electronegative atoms of another molecule to form a hydrogen bond.

This partial positive charge is essential for hydrogen bonds to occur. It makes the hydrogen atom act like a mini magnet that attracts the lone pairs of electrons on electronegative atoms in close proximity, allowing for the unique and life-sustaining properties of compounds like water.