Comparing Methane and Water's Properties

This question is quite chemical, and it's important to draw a diagram when answering it during the exam for both yourself and the marker to show a complete understanding of what is going on. Water is made of two hydrogen molecules and one oxygen molecule, and due to the strong pull that electrons feel in the presence of oxygen, they tend to spend more time in the oxygen area than in the hydrogen area. This results in oxygen having a partial negative charge, and hydrogen having a partial positive charge. This phenomenon is known as polarity, and is part of what makes it so important to a living organism, as it can bond with other polar molecules and exhibit hydrogen bonding with other water molecules. Methane on the other hand, is made of one carbon atom and 4 hydrogen atoms. Like water, the bonds are covalent. However unlike water, carbon does not pull the electrons as strongly as oxygen does, and the balanced number of hydrogen atoms means that the pull carbon exerts on the electrons is cancelled out, making the molecule nonpolar overall. Because of its absence of polarity, the interaction between methane molecules is considered to be very weak, and can easily be broken. The following numbers are important, but it is still possible to gain points on the question without having memorised these numbers, as at this point you have explained sufficient difference in the two molecules. Because water displays hydrogen bonding with other molecules, a large amount of heat energy is required to break this, and water's boiling point is around 100 degrees celsius. Unlike water, methane's weak interactive forces results in a very low boiling point of around -161 degrees celsius. Their differing properties also affects the energy required for a phase change in both molecules. For water to change from liquid to gas (known as latent heat of vaporisation), it requires 40.7 degrees celsius due to its hydrogen bonding, but for methane to change from liquid to gas it only requires 8.2 degrees celsius; an important fact to note in its impact on the environment which we can talk about later.