You are left with a chloride ion, so you started off with a chlorine atom.
Cl + e- → Cl-
Alkanes are saturated hydrocarbon, that is they contain hydrogen and carbon without a double or triple bond between the carbon atoms, e.g. ethane, propane. Group 7a in the periodic table are called halogens e.g chlorine, bromine. Alkanes react with halogens in a reaction called substitution, where halogens replace hydrogen atoms in alkanes.
You can take two liquids of different densities (how much mass is in a given volume) and pour them into a funnel. An example is oil and water. When the mixture settles, the denser liquid will be at the bottom, and drips through the funnel first. This is a separation that you can just let occur naturally.
Heat and gravity are fundamental to the process
The energy source for plate tectonics is Earth's internal heat while the forces moving the plates are the “ridge push” and “slab pull” gravity forces.
Hope I helped! :)
