Explain: at room temperature, methane(CH4) is a gas but water is a liquid.If possible, explain with reference to their molecular structure (shape)
It is known that water molecule consists of 2 atoms of hydrogen and 1 atom of oxygen, united by a covalent link, forming on the layer of valence 8 electrons (2 electrons from hydrogen with 6 electrons from oxygen ) and methane gas (CH4) has 4 atoms of hydrogen and 1 atom of carbon, still forming a covalent link, also with 8 electrons in valence layer (4 electrons from hydrogen and 4 from carbon ).
The chemical bonds pattern, especially localized valence bond model, it has nothing to do with the state of aggregation, melting point, etc.
Water is a liquid, with high boiling point due to hydrogen bonds between molecules,which are leading to molecular associations. Methane, having carbon as central atom, which is less electronegative as oxygen,it cannot form hydrogen bonds, so that the molecules cannot link together, leading to a lower boiling point.