Question

What is the hybridization of the central atom in (a) \(\mathrm{SiCl}_{4}\), (b) \(\mathrm{HCN}\), (c) \(\mathrm{SO}_{3}\), (d) \(\mathrm{ICl}_{2}^{-}\), (e) \(\mathrm{BrF}_{4}^{-}\) ?

Short answer

The hybridizations of the central atoms in the given molecules are: (a) \(\mathrm{SiCl}_{4}\): \(\mathrm{sp^3}\), (b) \(\mathrm{HCN}\): \(\mathrm{sp^2}\), (c) \(\mathrm{SO}_{3}\): \(\mathrm{sp^2}\), (d) \(\mathrm{ICl}_{2}^{-}\): \(\mathrm{sp^3}\), (e) \(\mathrm{BrF}_{4}^{-}\): \(\mathrm{sp^3d}\).

Step-by-step solution

Identify the central atom

In the molecule \(\mathrm{SiCl}_4\), the central atom is Si.

Calculate the total number of valence electron pairs

Si has 4 valence electrons and each Cl atom has 7 valence electrons. Since there are four Cl atoms that are bonded to the Si atom, we have a total of 4 bonds, which means 4 electron pairs around the central Si atom.

Determine the hybridization

Since Si has 4 electron pairs, the hybridization is \(\mathrm{sp^3}\). (b) \(\mathrm{HCN}\)

Identify the central atom

In the molecule \(\mathrm{HCN}\), the central atom is C.

Calculate the total number of valence electron pairs

C has 4 valence electrons, H has 1 valence electron, and N has 5 valence electrons. C forms a triple bond with N and a single bond with H. So, there are 3 electron pairs around the central carbon atom.

Determine the hybridization

Since there are 3 electron pairs, the hybridization is \(\mathrm{sp^2}\). (c) \(\mathrm{SO}_{3}\)

Identify the central atom

In the molecule \(\mathrm{SO}_{3}\), the central atom is S.

Calculate the total number of valence electron pairs

S has 6 valence electrons and each oxygen atom has 6 valence electrons. S forms double bonds with each of the three O atoms, resulting in a total of 3 electron pairs around the central sulfur atom.

Determine the hybridization

Since there are 3 electron pairs, the hybridization is \(\mathrm{sp^2}\). (d) \(\mathrm{ICl}_{2}^{-}\)

Identify the central atom

In the ion \(\mathrm{ICl}_{2}^{-}\), the central atom is I.

Calculate the total number of valence electron pairs

I has 7 valence electrons and each Cl atom has 7 valence electrons. In addition, there is one extra electron from the negative charge. I forms single bonds with the two Cl atoms and has a lone pair of electrons. As a result, there are 4 electron pairs around the central iodine atom.

Determine the hybridization

Since there are 4 electron pairs, the hybridization is \(\mathrm{sp^3}\). (e) \(\mathrm{BrF}_{4}^{-}\)

Identify the central atom

In the ion \(\mathrm{BrF}_{4}^{-}\), the central atom is Br.

Calculate the total number of valence electron pairs

Br has 7 valence electrons and each F atom has 7 valence electrons. In addition, there is one extra electron from the negative charge. Br forms single bonds with the four F atoms and has a lone pair of electrons. As a result, there are 5 electron pairs around the central bromine atom.

Determine the hybridization

Since there are 5 electron pairs, the hybridization is \(\mathrm{sp^3d}\).

Key concepts

Valence Electrons

Understanding valence electrons is crucial for predicting how atoms will bond and form molecules. These are the electrons located in an atom's outermost shell. They play a key role in chemical reactions and bonding, because they are the electrons involved in forming bonds with other atoms.

For example, in the molecule the outermost shell of Silicon (Si) has 4 valence electrons. Each Chlorine (Cl) atom contributes 7 valence electrons, resulting in the determination of Si's hybridization. Valence electrons determine how many bonds an atom can form, and therefore how it can interact with other atoms.

Electron Pairs

Electron pairs are pairs of electrons occupying the same orbital in a molecule. These pairs can be either shared between atoms (bonding pairs) or remain on one atom (lone pairs).

In molecular geometry, counting the number of electron pairs is a vital step since it helps determine the shape and hybridization of the molecule. For instance, in Silicon (Si) has 4 valence electrons that form 4 bonding pairs with Cl atoms, leading to 4 electron pairs around Si. These electron pairs dictate the hybridization of the central atom.

Central Atom

The central atom in a molecule is the one that atoms are bonded to. Typically, it is the atom with the lowest electronegativity or one that can form the most bonds at once.
For instance, in The central atom choice affects not only the shape of the molecule but also its hybridization. Recognizing the central atom early helps in predicting molecular geometry and chemical behavior.

Bonding

Bonding is the process where atoms combine by sharing or transferring electrons. It forms molecules by stabilizing atoms through the completion of their outer electron shells.

There are different types of bonding like covalent (shared pairs), ionic (transferred electrons), and metallic. In hybridization exercises, understanding the bonds an atom forms helps in determining the number and type of hybrid orbitals. For example, triple bonds, like in HCN between carbon and nitrogen, are counted as three electron pairs derived from bond sharing.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It is influenced by the number and type of electron pairs around the central atom.

This arrangement is crucial for understanding the physical and chemical properties of a substance like reactivity, polarity, phase of matter, and color. Each electron pair, whether bonding or lone, repels other pairs, leading to a particular shape. Such geometrical configuration is best explained by VSEPR (Valence Shell Electron Pair Repulsion) theory, which helps in predicting the molecular geometry based on the total number of electron pairs around the central atom.