Alkanes are a class of organic compounds that consist of only carbon (C) and hydrogen (H) atoms, bonded together by single covalent bonds. They are saturated hydrocarbons, meaning they have the maximum number of hydrogen atoms bonded to each carbon atom.
Alkanes can be identified by their molecular formula and their melting and boiling points. Here's how each of these factors contributes to their identification:
Molecular Formula: The molecular formula of an alkane provides information about the number of carbon and hydrogen atoms present in the molecule. Alkanes follow the general formula CnH2n+2, where "n" represents the number of carbon atoms. For example, methane (CH4) is the simplest alkane, ethane (C2H6) has two carbon atoms, propane (C3H8) has three carbon atoms, and so on. By knowing the molecular formula, you can determine the composition of carbon and hydrogen atoms in the alkane.
Melting Point and Boiling Point: The melting point and boiling point of alkanes increase with an increase in the size (number of carbon atoms) of the molecule. This is due to the increase in intermolecular forces, specifically van der Waals forces, as the size and surface area of the molecule increase. Larger alkanes have more extensive intermolecular interactions, resulting in higher melting and boiling points.
Additionally, branching in the alkane structure affects the melting and boiling points. Branched alkanes have lower boiling points compared to their straight-chain counterparts. This is because branching disrupts the close packing of molecules, reducing the surface area available for intermolecular interactions.
By comparing the molecular formulas and the melting and boiling points of different compounds, you can identify the alkane based on its carbon and hydrogen composition as well as the trends in melting and boiling points observed for alkanes.