Showing pi bonding through chemfig

Question

I've tried to make a diagram which shows pi bonding through chemfig, but I was not successful. Here is what I want.
_{(source: chem1.com)}

or

_{(source: uwaterloo.ca)}

Since I was unable to do it with chemfig I decided to do it with tikz. This is the best I could do:

\documentclass{article}
\usepackage{tikz}
\begin{document}

\begin{tikzpicture}

\shade[shading=ball, ball color=gray,draw,opacity=.7] (-2.5,0) .. controls (0,1) and         (.5,0.5) .. (.5,0)
.. controls (.5,-.5) and (0,-1) .. (-2.5,0);

\shade[shading=ball, ball color=gray,draw,opacity=.7] (2.5,0) .. controls (.5,1) and     (-.5,0.5) .. (-.5,0)
.. controls (-.5,-.5) and (.5,-1) .. (2.5,0);

\shade[shading=ball, ball color=gray,draw,opacity=.7] (-2.5,0) .. controls (-3.5,2.5)     and (-3,3) .. (-2.5,3)
.. controls (-2,3) and (-1.5,2.5) .. (-2.5,0);

\shade[shading=ball, ball color=gray,draw,opacity=.7] (-2.5,0) .. controls (-3.5,-2.5)     and (-3,-3) .. (-2.5,-3)
.. controls (-2,-3) and (-1.5,-2.5) .. (-2.5,0);

\shade[shading=ball, ball color=gray,draw,opacity=.7] (-2.5,0) .. controls (-4,0.5) and     (-5,0.83) .. (-4.5,1.5)
.. controls (-4,2.17) and (-3.5,1.31) .. (-2.5,0);

\shade[shading=ball, ball color=gray,draw,opacity=.7] (-2.5,0) .. controls (-4,-0.5)     and (-5,-0.83) .. (-4.5,-1.5)
.. controls (-4,-2.17) and (-3.5,-1.31) .. (-2.5,0);

\shade[shading=ball, ball color=gray,draw,opacity=.7] (2.5,0) .. controls (-3.5+5,2.5)     and (-3+5,3) .. (2.5,3)
.. controls (-2+5,3) and (-1.5+5,2.5) .. (2.5,0);

\shade[shading=ball, ball color=gray,draw,opacity=.7] (2.5,0) .. controls (-3.5+5,-2.5)     and (-3+5,-3) .. (2.5,-3)
.. controls (-2+5,-3) and (-1.5+5,-2.5) .. (2.5,0);

\shade[shading=ball, ball color=gray,draw,opacity=.7] (2.5,0) .. controls (4,0.5) and     (5,0.83) .. (4.5,1.5)
.. controls (4,2.17) and (3.5,1.31) .. (2.5,0);

\shade[shading=ball, ball color=gray,draw,opacity=.7] (2.5,0) .. controls (4,-0.5) and     (5,-0.83) .. (4.5,-1.5)
.. controls (4,-2.17) and (3.5,-1.31) .. (2.5,0);

\shade[shading=ball, ball color=blue,opacity=0.6] (4.5,1.5) circle (0.5);

\shade[shading=ball, ball color=blue,opacity=0.6] (4.5,-1.5) circle (.5);

\shade[shading=ball, ball color=blue,opacity=0.6] (-4.5,-1.5) circle (.5);

\shade[shading=ball, ball color=blue,opacity=0.6] (-4.5,1.5) circle (.5);

\end{tikzpicture}

\begin{tikzpicture}

\shade[shading=ball, ball color=gray,draw,opacity=.7] (-2.5,0) .. controls (0,1) and     (.5,0.5) .. (.5,0)
.. controls (.5,-.5) and (0,-1) .. (-2.5,0);

\shade[shading=ball, ball color=gray,draw,opacity=.7] (2.5,0) .. controls (.5,1) and     (-.5,0.5) .. (-.5,0)
.. controls (-.5,-.5) and (.5,-1) .. (2.5,0);


\shade[shading=ball, ball color=gray,draw,opacity=.7] (-2.5,0) .. controls (-4,0.5) and     (-5,0.83) .. (-4.5,1.5)
.. controls (-4,2.17) and (-3.5,1.31) .. (-2.5,0);

\shade[shading=ball, ball color=gray,draw,opacity=.7] (-2.5,0) .. controls (-4,-0.5)     and (-5,-0.83) .. (-4.5,-1.5)
.. controls (-4,-2.17) and (-3.5,-1.31) .. (-2.5,0);


\shade[shading=ball, ball color=gray,draw,opacity=.7] (2.5,0) .. controls (4,0.5) and     (5,0.83) .. (4.5,1.5)
.. controls (4,2.17) and (3.5,1.31) .. (2.5,0);

\shade[shading=ball, ball color=gray,draw,opacity=.7] (2.5,0) .. controls (4,-0.5) and     (5,-0.83) .. (4.5,-1.5)
.. controls (4,-2.17) and (3.5,-1.31) .. (2.5,0);

\shade[shading=ball, ball color=blue,opacity=0.6] (4.5,1.5) circle (0.5);

\shade[shading=ball, ball color=blue,opacity=0.6] (4.5,-1.5) circle (.5);

\shade[shading=ball, ball color=blue,opacity=0.6] (-4.5,-1.5) circle (.5);

\shade[shading=ball, ball color=blue,opacity=0.6] (-4.5,1.5) circle (.5);


\shade[shading=ball, ball color=black,draw,opacity=.7] (-2.5,0) .. controls (-3.5,2.5)     and (-3,3) .. (-2.5,3)
.. controls (0,2) .. (2.5,3)
.. controls (3,3) and (3.5,2.5) .. (2.5,0)
.. controls (1.5,1) .. (0,1)
.. controls (-2,1) .. (-2.5,0);


\shade[shading=ball, ball color=black,draw,opacity=.7] (-2.5,0) .. controls (-3.5,-2.5)     and (-3,-3) .. (-2.5,-3)
.. controls (0,-2) .. (2.5,-3)
.. controls (3,-3) and (3.5,-2.5) .. (2.5,-0)
.. controls (1.5,-1) .. (0,-1)
.. controls (-2,-1) .. (-2.5,-0);
\end{tikzpicture}

\end{document}

The end result is quite satisfactory, but

1. A shorter code would be nice
2. I am not sure how to use node and label pi bond and sigma bond(usage of quoate box would also look good), and label the atoms as well

Answer 1

Answer to your first question

You can keep your code short by applying for-loops in tikz code, like e.g.:

\foreach \i in {-4.5,4.5}
  \foreach \j in {-1.5,1.5}
    \shade[ball color=blue,opacity=0.6] (\i,\j) circle (.5) node{H};

Answer to your second question

It is possible to append at every point a node with some text like in the example above. The best advice that I can give you is to read the introducing examples in the manual or short introduction at CTAN or ask more details - there is a lot of stuff you might do with nodes...