Notes

Dot and Cross & Other Bonding Diagrams

The art of chemistry: drawing dot-and-cross diagrams and more

1. Do you cry in memes?

Art styles (left) vs chemistry styles (right)

There are many ways to complain about Chemistry! We can rant on Reddit, write a poem (that would be Lit af), or *cry in memes*. One emotion, many ways of expression. Likewise, artists draw the same thing in many different ways in fine art. In not-quite-fine chemistry, there are many ways to draw an oxygen molecule, from solid sphere to dot and cross diagrams.


2. Illustrating atoms and molecules as balls: the solid sphere model

Atoms as balls

This is the simplest diagram! And possibly the cutest, featuring water molecule as Mickey Mouse?

Here, atoms are reduced to spheres. We do not see the finer details, like electron shells and nucleus. We also do not see the type of bond between atoms. Best diagram if you want to smoke the teacher!

What you can tell from this diagram is:

  1. If a particle is an atom or a molecule
  2. If a particle is an element or a compound
  3. The number of elements in a molecule

3. Zoom out a bit please: showing the arrangement of many particles

Arrangement of particles in solid metal

We can also show the packing of particles in a large sample of solid, liquid, or gas by drawing many solid spheres.

This type of diagram is important for metallic bonding, to show the sea of delocalised electrons amidst regularly and closely packed metal cations.


4. Ball-and-stick diagrams

Like how the satay stick holds the two fishballs together, we show the invisible bond holding two atoms together as a stick. Not an advert for OCK though.

The unique feature of ball-and-stick diagram is the explicit display of bonding as lines, or “sticks”.

Representing the ionic bond of sodium chloride as sticks. Dodgy, but chemists do it!

A note of caution however. A single stick may not represent a single covalent bond. In fact, the bond may not even be covalent!


5. Leaving traces: dot and cross diagrams for ionic bonding

Unlike the solid sphere model and ball-and-stick diagram, dot and cross diagrams tell us everything about the electronic configuration of the particles upon bonding.

Dot and cross diagram of magnesium fluoride, showing only the outer electron

The diagram is like a crime scene! You see traces of electron transfer. Firstly, the charges written as superscripts tell you that magnesium and fluoride exist as ions here. Secondly, each fluoride has got one electron stolen from magnesium ion. And rather unfortunately for magnesium, it encountered two fluorides, stealing both its hitherto valence electrons to reveal the inner shell as shown here in the diagram.


6. Overlapping and embracing: dot and cross diagrams for covalent bonding

Single, double, and triple covalent bonds are represented by two, four, or six electrons in the overlapping region.

The overlap between the two circles bear witness to the sharing of electrons between the two atoms. The more dots and crosses you see inside, the greater the number of covalent bonds.

Number of Shared ElectronsType of Covalent Bond
2Single bond
4Double bond
6Triple bond

7. Simplified dot and cross: structural formula

Showing more with less

Too tiring to draw the dots and crosses?

Structural formulae come to your rescue. Simply show the single, double, or triple bonds as one, two, or three parallel lines respectively.