\documentclass[a4paper,twocolumn]{article}
\usepackage{tabularx,booktabs}
\usepackage{kantlipsum}
\begin{document}
\kant[1-3]
\begin{table}
\centering
\caption{Some caption
\label{tab:label}}
\begin{tabularx}{\textwidth}{ X X X }
\toprule
$\alpha$ & $\beta$ & $n$ \\
1 & 2 & 3 \\
\bottomrule
\end{tabularx}
\end{table}
\kant[1-3]
\end{document}