Solutions

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For each molecule on the worksheet, the Lewis Dot Structure, the number of valence electrons, the electron arrangement (E.A.) and the molecular geometry (M.G.) are given, respectively. To see a larger view of the Lewis Dot Structure, point at the molecule, right click on the mouse and go to 'View image'.

Lewis Dot works best for covalent compounds of group A elements, though Lewis Dot Structures can explain electron transfer in ionic compounds. By following the rules below, the Lewis Dot Structure can be written for covalent compounds and some polyatomic ions.

Count the total number of valence electrons, adjust for charge if an ion. Add one electron for each negative charge, subtract one electron for each positive charge.
Place a pair of electrons between the central atom (usually written first) and each of the outer atoms.
Complete the octet of the outer atoms (except H, which needs only 2 electrons).
Place extra electrons, if any, on the central atom in pairs.
If the central atom does not have a complete octet, share extra electrons from the outer atoms until the central atom and the outer atoms have a complete octet. Note: halides do not form double bonds.

PF₅	40 electrons tbp tbp	CS₂	16 electrons linear linear	BrO₃^-	26 electrons Td trigonal pyr.

NH₄⁺	8 electrons Td Td	SCl₄	34 electrons tbp see-saw	BrF₅	42 electrons Oh square pyr.

BF₃	24 electrons trigonal planar trigonal planar	SCl₆	48 electrons Oh Oh	PH₃	8 electrons Td trigonal pyr.

NF₃	26 electrons Td trigonal pyr.	SO₄²^-	32 electrons Td Td	CO₃²^-	24 electrons trigonal planar trigonal planar

SiCl₄	32 electrons Td Td	ClO₃^-	26 electrons Td trigonal pyr.	CH₂O	12 electrons trigonal planar trigonal planar

NO₃^-	24 electrons trigonal planar trigonal planar	O₃	18 electrons trigonal planar bent	CCl₄	32 electrons Td Td

AlH₃	6 electrons trigonal planar trigonal planar	SO₂	18 electrons trigonal planar bent	SO₃	24 electrons trigonal planar trigonal planar

CO	10 electrons linear linear	CHCl₃	26 electrons Td Td	BrF₃	28 electrons tbp T-shaped

H₂S	8 electrons Td bent	I₃^-	22 electrons tbp linear	H₃O⁺	8 electrons Td trigonal pyr.