\documentclass[tikz]{standalone}

\pgfmathdeclarerandomlist{colors}{{red!80}{teal}{blue!80}{orange}{blue!20}}

\begin{document}
\begin{tikzpicture}
  \foreach \i in {1,...,12} {
      \foreach \j in {1,...,4} {
          \foreach \k in {1,...,4} {
              \pgfmathrandomitem{\randColor}{colors}
              \shade[ball color=\randColor] (-\i+0.3*\j, -0.2*\j+1.2*\k) circle(0.3);
            }
          \foreach \k in {1,...,3} {
              \pgfmathrandomitem{\randColor}{colors}
              \shade[ball color=\randColor] (-\i+0.5+0.3*\j, -0.2*\j+1.2*\k+0.6) circle(0.3);
            }
        }
    }
  \foreach \el/\color [count=\n] in {Al/red!80, Co/blue!80, Cr/teal, Fe/orange, Ni/blue!20} {
      \shade[ball color=\color] (2, 5.5-\n) circle(0.3) node[right=1em] {\el};
    }
\end{tikzpicture}
\end{document}