Imagine a single atom responsible for every organic and a few inorganic elements you see on Earth! Diamonds, methane, and even the molecules in your body. That’s sp³ Carbon—and in the next few minutes, we will see what it is and why it’s chemistry’s ultimate VIP!”
A Carbon atom can build everything from the fuel in your car to the hardest gem. The secret is in Carbon’s sp3 superpower.
When atoms engage to form molecules, they do so by the overlap of atomic orbitals, creating a bigger molecular orbital that now encompasses more than one atom of a molecule.
Dihedral Angle | Bond Angle | |
|---|---|---|
Definition |
Aspect | Valence Bond Theory (VBT) | Molecular Orbital Theory (MOT) |
|---|---|---|
Basic Concept | Describes chemical bonding as the overlap of atomic orbitals, forming localized bonds. | Describes bonding by combining atomic orbitals into molecular orbitals that are delocalized over the molecule. |
Bonding Explanation | Focuses on bonds as being localized between two specific atoms. |
Aspect | Atomic Orbitals (AOs) | Molecular Orbitals (MOs) |
|---|---|---|
Definition | Simple regions around the nucleus of an atom where there’s a high probability of finding an electron and these regions is represented as spheres, or lobes. | A region in a molecule where electrons are likely to be found, formed by the combination of atomic orbitals of two or more atoms. |
If you look at the shape of s and p orbitals before hybridization, you will notice that -
The s orbital is spherical.
The p orbital is dumbbell-shaped, where the two lobes are proportionate along one axis.
However, when these orbitals of the same atom mix to form hybrid orbitals, the newly formed shape is that of teardrops pointing in opposite directions, with one lobe more prominent than the other.
The arrangement of groups around a central atom creates its three-dimensional shape. And this shape affects how it interacts with other molecules or ions.
The interactions could be bonding - to form new bonds or nonbonding- affecting the physical properties of solubility, melting point, boiling point, polarity, and more.
| sp3 | sp2 | sp |
|---|---|---|---|
Orbitals involved | One s and three p-orbitals of the central atom that are close in energy mix to form four sp3 hybrid orbitals for covalent bond formation. |
The molecule H2N-NH2, also known as hydrazine, each Nitrogen atom has 3 bond pairs (two N-H and one N-N bonds) and one lone pair. So, the steric number of each Nitrogen atom is,
steric number=number of bond pairs + number of lone pairs
steric number=3 + 1 = 4
The bond angle is the angle at which two adjacent bonds converge and meet at the central atom in molecules.
The very premise of a covalent bond is electron sharing. As two atoms share one electron each to form one covalent bond, they may likely share more than once and form more bonds. This information on the number of connections between two atoms is revealed from the Bond Order.
So, the Bond Order measures the number of bonds between the two atoms in a molecule. The number can be integers like 1, 2, or 3 for single, double, or triple bonds or non-integers like 0.5, 1.3, 1.5, etc.
Bond lengths are smaller when atoms form multiple bonds. Single overlap between two atoms forms a single covalent bond. So, when they overlap twice and thrice to form double and triple bonds the atoms to come closer to form a tight-knit. Such bonds are even harder to break. So, the bond length of a triple is smaller than a double and single bond.
An easy way to identify organic compounds is to look for several atoms in a long chain. These long chains are covalent bonds. So, the length of the bond and the factors affecting it becomes very important.
Such a bond formation occurs only when the atoms that want to form covalent bonds have the right concentration, orientation, and speed.
Did you know that, back in the 1900s, it was believed that a hook and a loop type of closure was the covalent bond responsible for holding atoms in a molecule? Interesting, right?
Valence Bond (VB) Theory | Valence Shell Electron Pair Repulsion (VSEPR) Theory |
|---|---|
Valence Bond Theory explains how atoms combine to form di and polyatomic molecules held by covalent bonds. | VSEPR theory considers shape, molecular geometry, and bond angles as an after-effect of covalent bond formation. The molecules take up various shapes to overcome the electron repulsions between the bonding and nonbonding electrons of the combining atoms. |
When an atom is surrounded by six substituents, arranged in a manner that four are in one plane, one above and below, and their vertices join to give eight faces (octa-hedrons), such a molecular geometry is octahedral.
Since it looks like two pyramids projecting out from a square base, the geometry is also called square bipyramidal.
A bond angle is a geometrical angle between two bonds originating from the same central atom in a covalently bonded molecule, measured in degrees (o).
Sigma bond | Pi bond | |
|---|---|---|
Formation | The sigma bond is formed by the head-to-head (or end-to-end) overlap of the hybrid or atomic orbitals. | A pi bond is an additional bond over the sigma bond formed by the side-to-side (or lateral) overlap of the perpendicular p-atomic orbitals. |
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Once the sigma bonds are formed, any additional electrons in the perpendicular unhybridized p-atomic orbitals engage in side-to-side or lateral overlap to form an additional bond known as the pi bond. The symbol π denotes the pi bond, drawn as an additional line over the sigma bond in the molecular structure.
The single covalent bond is referred to as a sigma bond, denoted by the symbol σ.
The sigma bonds are usually mentioned in valence bond theory to visualize the bond formation between atoms to form polyatomic molecules like H2, CH4, etc., by overlapping their atomic orbitals.
| Heterolytic | Homolytic |
|---|---|---|
Cleavage | The two-electron bond between two heteroatoms breaks unequally. | The two-electron bond between two similar or dissimilar atoms breaks equally. |
By-Product | The by-product of the reaction is the generation of two intermediates-cation and an anion. |
Heterolytic cleavage or heterolysis is a chemical reaction in which the bond between two atoms breaks unequally so that the two bond electrons reside with only one atom.
The atom that receives both electrons become an electron-rich negatively charged ion (anion, denoted with a negative sign), and the atom that lost the electrons forms a positively charged ion (cation, denoted with a positive sign).
Homolytic cleavage, or homolysis, is a chemical reaction in which a covalent bond between two atoms is broken equally, and each atom retains one of the two electrons that form the bond. This creates two species (similar or dissimilar), each with an unpaired electron, known as the radicals. The radical electron is denoted with a dot (.) over the atoms’ symbol.
In his landmark paper, 'The Atom and the Molecule,' G.N. Lewis attempted to describe linkages between the atoms to understand the nature of covalent bonds.
He used dots to represent an atom’s valence electrons and argued that the atoms share their valence electrons to form one, two, or three bonds until they attain a stable octet electron configuration. An exception is the Hydrogen atom that attains a duplet configuration.
In molecules consisting of more than two atoms, the least electronegative atom (except Hydrogen) is the central atom. Due to its low electronegativity, the central atom will not hoard electrons but will share with other atoms, thereby forming a maximum number of bonds than the terminal atoms. So, the central atom is also the least numerous.
In a regular trigonal planar molecular geometry, a central atom is surrounded by three equally spaced substituents in one plane, so joining the three corners would give a triangle.
In a regular tetrahedral molecular geometry, a central atom is surrounded by four substituents that occupy the four corners of a tetrahedron. The substituents are called ligands if the central atom is a metal.
Dalton, in 1804, in his work on ‘Atomic Theory,’ proposed the law of chemical combination to explain how atoms form compounds. According to him, atoms of different elements combine in a simple whole-number ratio to give compounds.
For example, two Hydrogen and one Oxygen combine to form water (H2O), or four Hydrogens and one Carbon combine to form methane (CH4), or one Nitrogen combines with three Hydrogens to give ammonia (NH3).
If a two-electron covalent bond breaks symmetrically, each of the two atoms receive one electron; it is a homolytic bond cleavage.
A homolytic cleavage is shown using a fish-hook arrow, which implies one-electron movement.
Pre-Requisite Reading: Electronegativity
A covalent bond is formed between two similar or dissimilar atoms (Ex: Carbon-Carbon and Carbon-Halogen).
A covalent bond holding two atoms is made of two electrons. The bond can cleave or break in two ways - equally (homolytic fission) or unequally (heterolytic fission).
A heterolytic bond cleavage results in unequal bond-breaking where one atom in the bond retains both the bond electrons.
When two atoms come closer by attraction and overcome their repulsive interactions until they find a balance, at which point, the atoms contribute one valence electron each to form a stable, single covalent bond. So, the single covalent bond is a two-electron bond.
It is also known as the sigma bond and is denoted as a dash (-) between the two atoms.
A sp3 hybridized carbon is a tetravalent carbon that forms four single covalent bonds with itself or atoms of other p-block elements to its right, namely Oxygen, Carbon, Nitrogen, and Halogens. It also forms a bond with elements capable of forming covalent bonds, such as hydrogen.
The bonds formed are of equal strength and at an angle of 109.5o due to which the central carbon atom is tetrahedral in shape. Example, carbon of an alkane or an alkyl group.
The three common hybridization states are - sp3, sp2, and sp. The sp3 (pronunciation: ess-pee-three) hybridization of Carbon explains its four bonds’ tetravalency, shape, and equivalency.