Question Video: Understanding Relative Charge in a Pentavalent-Doped Semiconductor | Nagwa Question Video: Understanding Relative Charge in a Pentavalent-Doped Semiconductor | Nagwa

Question Video: Understanding Relative Charge in a Pentavalent-Doped Semiconductor Physics • Third Year of Secondary School

The diagram shows a lattice of silicon atoms that contains one atom of phosphorus. One of the electrons from the outermost shell of the phosphorus atom moves freely in the lattice. What is the net relative electronic charge of the phosphorus?

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Video Transcript

The diagram shows a lattice of silicon atoms that contains one atom of phosphorus. One of the electrons from the outermost shell of the phosphorus atom moves freely in the lattice. What is the net relative electronic charge of the phosphorus?

To begin, recall that a neutral phosphorus atom has five electrons in its outermost electron shell. This diagram shows that when phosphorus is in a silicon lattice, the four neighboring silicon atoms share electrons in covalent bonds with phosphorus. Recall that there is only room for eight possible electrons in the outermost shell. And so four electrons in the shell are shared from neighboring atoms, and the other four came with the phosphorus atom originally. But phosphorus did come with five outermost electrons. And there isn’t room for any more electrons in the shell now that it’s in the lattice. So, that one extra electron has become liberated as a free electron.

So the phosphorus was originally neutral. And then it lost one electron, which has a relative charge of negative one. This means that the phosphorus now has a net positive charge value. Therefore, the net relative electronic charge of the phosphorus atom in the lattice is positive one.

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