1.44 - 1.46 Covalent bonding - "sharing nicely"
1.44 Sharing electrons
In the previous topic you will have seen how ionic compounds are formed when the atoms of metals transfer electrons to the atoms of non-metals. The electron transfer enables the atoms to fill their outer electron shells and become stable.
Assumed background knowledge:
1.44 - 1.45 Activity 1. Opposites attract
Play the video to see an animation showing the way in which electrons shared between two nuclei will create an electrostatic attraction between them. This attractive force is known as a covalent bond.
Notice that as the bond forms, energy is released.
It follows then that to break a bond, energy needs to be supplied.
1.46 Activity 2. Crossing and dotting
- 1.46 understand how to use dot-and-cross diagrams to represent covalent bonds in molecules.
Watch the video and notice that:
1.46 Activity 3. Four simple molecules
- Study the animation carefully.
- What can you say about the number of electrons in the outer shell of the carbon atom in methane, the nitrogen atom in the ammonia molecule and the oxygen atom in the water molecule?
- Make a copy of each of the images below and add dots and crosses to them to show the complete electron configurations
1.46 Activity 4. Multiple Bonds
Going further .. a toxic gas
What is unusual about one of the bonds in carbon monoxide? Open or Close
The dot and cross diagram shows that a triple bond forms in the carbon monoxide molecule. It also shows that in one of the triple bonds, both electrons come from the oxygen atom.
This type of bond is still an ordinary covalent bond but is is known as a dative covalent bond. Such bonds are sometimes represented by an arrow.
Study the dot and cross diagrams for each of the three molecules shown in the animation.
Notice that for ethane and ethene two different colours of cross have been used to distinguish the electrons associated with one of the carbon atoms from the electrons on the other. The same method is used to distinguish Chlorine's electrons from the carbon's electrons in the chloromethane.
Think about the formula, shape, structure and name of each of the molecules shown.
Predicting an unknown molecule
- Try to draw a 3d representation of chloroethene
- Try to draw a dot and cross diagram to show the electron arrangement in chloroethene