Dot and Cross Diagrams

A dot and cross diagram is useful for showing the bonding in small molecules. It shows the arrangement of electrons in a molecule. Here’s how to draw a dot and cross diagram:

1. Draw a circle for each atom in the molecule. This circle represents the outermost shell of the atom.

2. To represent a covalent bond, overlap two circles. This shows that the electrons in the outer shell of each atom are shared between the two atoms.

3. Use dots and crosses to represent the electrons in the shell. The dots and crosses should be placed within the circles, indicating which electrons belong to which atom.

4. Make sure that each atom has the correct number of electrons.

Drawing electrons as dots and crosses makes it easier to tell which electron belongs to each atom. For example, you can see the dot and cross diagram for a hydrogen molecule below, which has the formula H2.

The image illustrates a simple atomic diagram of a hydrogen molecule, consisting of two hydrogen atoms (denoted by the symbol "H") bonding together. Each hydrogen atom is represented with a circle. Within the overlapping region of these circles, there's a depiction of two electrons: one marked with an "x" and the other as a solid blue dot, symbolising the shared electron pair in the covalent bond between the two hydrogen atoms.

Stick Diagrams

Stick diagrams are useful for showing the bonding in large covalent molecules. Instead of representing electrons as dots and crosses, you simply write the chemical symbols of the atoms and use lines to show the bonds between them. For example, the stick diagram of the hydrogen molecule is:

Two 'H' symbols (representing hydrogen atoms) are connected with a line, symbolising a single covalent bond.

The number of lines between the atoms represents the number of covalent bonds between them. For example, if two atoms are bonded together with a single bond, there will be one line connecting them. If they are bonded with a double bond, there will be two lines.

Stick diagrams are a quick and simple way to represent the structure of large and complex molecules. Drawing dot and cross diagrams for these molecules can be time-consuming, as you have to draw all of the outer electrons and energy levels. Stick diagrams can also help you see the overall shape of a molecule.

Comparing Diagrams of Different Molecules

Let’s look at the dot and cross diagrams and stick diagrams for some more molecules.

Chlorine molecule

Dot and cross:

A dot and cross diagram of two chlorine atoms. Electrons from one atom are represented with crosses, and the other with dots. Within the overlapping region of the circles, a cross and a dot signify the shared electrons, representing a covalent bond.

Stick diagram:

2 sets of the letters "Cl" representing chlorine atoms. A single line connecting them represents the single covalent bond.

Oxygen molecule

Dot and cross:

A dot and cross diagram of two oxygen atoms, each sharing two electrons, forming a double covalent bond.

Stick diagram:

2 "O's" representing Oxygen atoms with 2 lines between them representing the double bond.

Water molecule

A water molecule (H2O) is made up of two hydrogen atoms and one oxygen atom. They are bonded together by covalent bonds.

In a dot and cross diagram, you can see that the oxygen atom has eight electrons in its outer energy level, which it shares with the two hydrogen atoms. The hydrogen atoms each have one electron in their outer energy level, and they bond with the oxygen atom by sharing an electron pair. This forms two covalent bonds and helps to complete the outer energy level of all three atoms.

Dot and cross:

Two hydrogen atoms, each sharing an electron with a single oxygen atom. The crosses from the hydrogen are present in the overlapping section with the oxygen atom, indicating shared electrons.

In the stick diagram, bonds between the hydrogen and oxygen atoms are represented by lines. The overall structure of the water molecule is bent, with the oxygen atom in the centre and the hydrogen atoms attached to it at an angle.

Stick diagram:

2 lines linking an "O" (representing Oxygen) to 2 "H's" (representing Hydrogen).

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