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Wonderful thinking! If Hydrogen gets \(1\) electron, it will have \(2\) electrons in its \(n=1\) orbit. That makes Hydrogen stable. So, Hydrogen's valency is \(1\). Also, Helium already has \(2\) electrons in its outermost orbit. So, it is already stable, and doesn't need to get or give away electrons. So, its valency is \(0\).
As we discussed earlier, atoms have an equal number of electrons and protons. This number is called the atomic number and is represented by \(Z\)

\(\text{Atomic Number}\) \(= \text{Number of protons}\)
What is the atomic number of Beryllium? (The red plus signs in the nucleus are protons.)
  • \(2\)
  • \(3\)
  • \(4\)
  • \(8\)