Let's look at phosphorus.

Because phosphorus is in group 5A it has five valence electrons.

• First thing to do is check the group numbers.
• Phosphorus is in group 5A.
• Phosphorus has 5 valence electrons, 3s²3p³.
• Some math tells us that the phosphorus can accept three electrons to complete the valence shell octet.
• This means that phosphorus will form three covalent bonds to complete an octet and gain a share of three electrons.

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