Question

5. A step in determining Lewis formulas is to find the total number of valence

     electrons that are used in the formulas. Find such totals for the following:

     A. CS₂ B. PCl₃ C. SO₃^2- D. CH₄ E. Cl₂

Answer 1

A) CS2 carbon is in IV A of perodic table, thus has 4 valence electrons and needs four more to complete octet.

S is in VI group with 6 valence electrons and needs two more to have octet.

Thus caron contributes two electrons each with each sulfur forming double bonds,sharing a total of four pairs of electrons and the Lewis structure is S=C=S

B) P belongs to V A group with 5 valence electrons , thus in need of three more to get octet and each chlorine has 7 electrons in valence shell which require only one more to complete octet.

Thus P contributes one electron each for bonding with chlorine and in turn shares two with each completing its octet. Chlorin also contributes one electron and shares a pair to complete its octet.

C) S has 6 valence electrons and oxygen also has 6 valence electrons. However two oxygens that possess the negative charge have 7 valence electrons in their valence shell.Thus S contributes two electrons with one oxygen,sharing 4 electrons and one electron with the remaining two oxygens with negative charge sharing a pair of electrons with each . thus both S And O complete their octet.

D) Caron has 4 valence electronsand each hydrogen only one valence electron. Thus carbon contributes one electron each with hydrogens and sharing a pair of electrons mutualy with each hydrogen .

E) chlorine has 7 alence electrons as it is in VII A group. Hence it needs one more to complete octet. Thus each chlorine contributes one for bonding sharing apair of electrons.