So we're basically going to take two methane molecules, combine them, and form our ethylene. But before we actually combine them, we have to turn them into methyl radicals. A methyl radical is simply a methane molecule minus an h atom and an electron. So to create a methyl radical from a methane molecule, we take away an h atom along with one electron. But the same thing goes for this second methane molecule. We take away an h atom along with one electron.