Explain why the Lewis Symbol for helium, He:, only has a duet of electrons. 2. C

Question

Explain why the Lewis Symbol for helium, He:, only has a duet of electrons. 2. Compare the number of valence electrons you drew for phosphorus above to the number of electrons a neutral phosphorus atom has (i.e., the atomic number). Where are the other electrons? 3. Name two elements that commonly have an incomplete octet when they are the central atom in a compound. 4. Explain why elements in Periods 1 and 2 cannot have expanded octels, while those in Period 3 and higher can exhibit expanded valence shells. Based on this premise, which one of the following compounds would you least expect to form: PF_5 or NF_5?

Explanation / Answer

2) number of valence electrons in Phosphorus = 5
number of electrons in Phosphorus = 15
Valence electrons resides in M-shell (3rd shell) while other electrons reside in inner shells- K-shell (1st shell) and L-shell (2nd shell)

3) Berylium, Boron
When Berylium & Boron are central atoms, they form two and three bonds respectively.
Two bonds (4 electrons) => incomplete octet
Three bonds (6 electrons) => incomplete octet

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