Question

question
decide whether the lewis structure proposed for each molecule is reasonable or not.

• if two or more atoms have the wrong number of valence electrons around them, just enter the chemical symbol for the atom as many times as necessary. for example, if two oxygen atoms have the wrong number of electrons around them, enter the symbol o twice.

Explanation:

Step1: Calculate valence electrons for \(ClF_3\)

Chlorine (\(Cl\)) has \(7\) valence electrons and each fluorine (\(F\)) has \(7\) valence electrons. For \(ClF_3\), the total number of valence electrons is \(7+(3\times7)=28\). In the proposed structure, there is a double - bond between \(Cl\) and \(F\). Fluorine should form only single bonds (as it has \(7\) valence electrons and needs one more to complete octet). So, some atoms have the wrong number of electrons around them.

Step2: Calculate valence electrons for \(PO_4^{3 -}\)

Phosphorus (\(P\)) has \(5\) valence electrons, each oxygen (\(O\)) has \(6\) valence electrons and there is a charge of \(3-\). The total number of valence electrons is \(5+(4\times6)+3 = 32\). In the proposed structure, phosphorus has double - bonds with two oxygens. In a more common and correct Lewis structure (using the octet rule for \(P\) in a non - expanded form), \(P\) forms single bonds with all four \(O\) atoms (although \(P\) can have expanded octet, but if we consider the simple octet - based approach for the error in the given structure), the given structure has \(P\) with an incorrect electron count (if we assume non - expanded octet preference for the error analysis here, as the structure shows double bonds which would make \(P\)'s electron count wrong in a simple octet - only view). So, some atoms have the wrong number of electrons around them.

Step3: Calculate valence electrons for \(AlCl_3\)

Aluminium (\(Al\)) has \(3\) valence electrons and each chlorine (\(Cl\)) has \(7\) valence electrons. The total number of valence electrons is \(3+(3\times7)=24\). Aluminium in \(AlCl_3\) has only \(6\) electrons around it (violating the octet rule for \(Al\) in a simple Lewis structure view, although \(AlCl_3\) can form dimers in some states, but for the given Lewis structure), so some atoms have the wrong number of electrons around them.

Answer:

• For \(ClF_3\): No, some atoms have the wrong number of electrons around them. The symbols of the problem atoms are: \(Cl\), \(F\)
• For \(PO_4^{3 -}\): No, some atoms have the wrong number of electrons around them. The symbols of the problem atoms are: \(P\)
• For \(AlCl_3\): No, some atoms have the wrong number of electrons around them. The symbols of the problem atoms are: \(Al\)