Question

When two species A and B form an electron pair bond and A does not provide its electrons for bonding, the bond present between \(\mathrm{A}\) and \(\mathrm{B}\) must be (1) ionie (2) covalent (3) dative (4) hydrogen

Short answer

The bond is dative.

Step-by-step solution

- Understand the problem

Two species, A and B, form a bond where A does not provide any electrons for bonding.

- Identify bond types

Different types of bonds include ionic, covalent, dative, and hydrogen bonds. Ionic bonds involve transfer of electrons, covalent bonds involve sharing of electrons, dative bonds involve both electrons in the bond being provided by one atom, and hydrogen bonds are weak attractive forces between a hydrogen atom and an electronegative atom.

- Analyze the scenario

Since A does not provide electrons for bonding, we can exclude ionic and covalent bonds. Hydrogen bonds are weak and typically involve hydrogen.

- Determine the bond type

Since both electrons in the bond come from one atom (B), the bond formed between A and B is a dative bond.

Key concepts

ionic bonds

When atoms or molecules interact to form compounds, one possible type of chemical bond that can be formed is called an ionic bond. This type of bond occurs when one species (usually a metal) transfers one or more electrons to another species (usually a non-metal).
The result is the formation of positively charged cations and negatively charged anions, which attract each other due to their opposite charges.
This strong electrostatic attraction between ions is what holds the compound together.

• An everyday example of an ionic bond is table salt (NaCl), where sodium (Na) transfers an electron to chlorine (Cl).

In an ionic bond, the difference in electronegativity between the two atoms is typically significant, leading to the complete transfer of electrons and the formation of ions.

covalent bonds

Another way in which atoms can bond is through a covalent bond. In this type of bond, atoms share pairs of electrons to achieve a more stable electron configuration, often fulfilling the octet rule.
Unlike ionic bonds, covalent bonds do not involve the transfer of electrons, but rather the sharing of electrons between atoms, typically non-metals.

• For example, in a molecule of water (H₂O), each hydrogen atom shares an electron with the oxygen atom.

Covalent bonds can be single, double, or triple bonds, depending on the number of shared electron pairs. Single bonds share one pair, double bonds share two pairs, and triple bonds share three pairs of electrons. The strength and length of these bonds vary, with triple bonds being the strongest and shortest.

dative bonds

A dative bond (also known as a coordinate covalent bond) is a unique type of covalent bond where both electrons in the bond originate from the same atom.
This type of bond occurs when one atom has a lone pair of electrons to donate and another atom has an empty orbital to accept them.
Once formed, dative bonds are indistinguishable from regular covalent bonds.

• A common example of a dative bond is the formation of the ammonium ion (NH₄⁺), where the nitrogen atom donates a pair of electrons to a proton (H⁺).

In the given exercise scenario, species A does not provide any electrons, indicating that the bond with species B must be dative, as B donates both electrons.

hydrogen bonds

Another important interaction in chemistry is the hydrogen bond, which is often weaker than ionic and covalent bonds but plays a crucial role in the properties of many substances.
Hydrogen bonds occur when a hydrogen atom, covalently bonded to a highly electronegative atom (like oxygen, nitrogen, or fluorine), experiences an attraction to another electronegative atom in a nearby molecule.

• Water (H₂O) is a well-known example where hydrogen bonds occur between water molecules, giving water its unique properties such as high boiling point and surface tension.

Hydrogen bonds are essential in biological systems, including the secondary structure of proteins and the formation of the DNA double helix. Even though they are relatively weak compared to ionic and covalent bonds, their cumulative effect can significantly influence the characteristics of compounds.