What does a double bond represent? Give two examples of molecules in which double bonds occur, a

What does a double bond represent? Give two examples of...

Key Concepts

Double Bond

A double bond is a type of covalent bond where two pairs of electrons are shared between two atoms. This typically involves one sigma bond, which forms from the head-on overlapping of orbitals, and one pi bond, which is created by the lateral overlapping of adjacent p-orbitals. The presence of a double bond affects the molecule by imposing a rigid planar structure and influencing its chemical reactivity.

Sigma and Pi Bonds

In a double bond, the sigma (?) bond is the first bond formed and arises from the direct overlap of atomic orbitals along the line connecting the nuclei, providing a strong, stable bond. The pi (?) bond, which is the second bond, results from the sideways overlap of p-orbitals above and below the axis of the sigma bond. Together, these bonds determine the strength and geometry of the overall double bond.

Lewis Structures

Lewis structures are graphical representations of molecules that depict the bonds between atoms and the lone pairs of electrons. They are used to illustrate how valence electrons are arranged around atoms, including the formation of double bonds, and serve as essential tools for predicting molecular geometry, reactivity, and electron distribution.

Transcript

00:01 A double bun is a chemical bond in which two sets of valence electrons, also known as the outermost electrons, as shared by two atoms.

00:10 The first example we look at is ethene, c2, h4.

00:18 Carbon has four valence electrons, and hydrogen has one valence electron.

00:41 To represent ethene structurally, we have c -double bun c, then c single bun h.

01:02 So to look at the electrons, looking at carbon, one electron from the c double one c, one electron came from the carbon and the other election came from the other carbon to the right.

01:22 And below, one electron came from carbon also.

01:27 And the other electron also came from the other carbon to the right.

01:31 So now you have two sets of valence electrons represented by the double bond.

01:43 And if you look at the carbon to hydrogen bond, one electron came from hydrogen from carbon and the other electron from hydrogen.

01:55 Same thing for the other carbon hydrogen bond, one electron from carbon, the other electron from hydrogen.

02:07 So carbon, if you count the number of electrons, there will be eight electrons because there are four bonds, the carbon, and each bond represents two electrons.

02:27 So carbon has eight outer electrons.

02:31 So its octet is completed.

02:34 Hydrogena, however, needs two electrons for it to be stable...

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