# Aligning chemical elements in a reaction equation

As pictures tell the issue better than I could I'm just gonna insert a screenshot of the problem right off the bat.

My problem is concerning the undesired whitespace between the second column of five elements and the five pluses before the five n's. LaTeX code of same looks like this:

\documentclass[12pt]{article}

% Maths & Chemistry Preamble %
\usepackage{amssymb, amsmath}
\usepackage{mhchem}

\begin{document}

\ce{^{235}_{92}U + ^{1}_{0}n -> ^{236}_{92}U^{*} ->[\text{85\% nuclear fission}]} \begin{cases} \begin{align*} \ce{^{144}_{56}Ba &+ ^{89}_{36}Kr &+ 3^{1}_{0}n} \\ \ce{^{144}_{55}Cs &+ ^{90}_{37}Rb &+ 2^{1}_{0}n} \\ \ce{^{140}_{54}Xe &+ ^{94}_{38}Sr &+ 2^{1}_{0}n} \\ \ce{^{146}_{57}La &+ ^{87}_{35}Br &+ 3^{1}_{0}n} \\ \ce{^{160}_{62}Sm &+ ^{72}_{30}Zn &+ 4^{1}_{0}n} \end{align*} \end{cases} \label{eq:u_1}

Packages used are amsmath, amssymb and mhchem. All I want to achieve is to have the pluses in line while minimizing the space to the left of them.

Just use an array here. You may want to add one more @{} or some other spacer onto the left of the first column.

% arara: pdflatex

\documentclass[12pt]{article}
\usepackage[version=4]{mhchem}
\usepackage{siunitx}

\begin{document}
\setcounter{equation}{4}
$$\ce{^235_92U + ^1_0n -> ^236_92U^* ->[{\SI{85}{\percent} nuclear fission}]} \left\{\renewcommand{\arraystretch}{1.2}\begin{array}{l@{} l@{} l@{}} \ce{^144_56Ba &+ ^89_36Kr &+ 3^1_0n} \\ \ce{^144_55Cs &+ ^90_37Rb &+ 2^1_0n} \\ \ce{^140_54Xe &+ ^94_38Sr &+ 2^1_0n} \\ \ce{^146_57La &+ ^87_35Br &+ 3^1_0n} \\ \ce{^160_62Sm &+ ^72_30Zn &+ 4^1_0n} \end{array}\right. \label{eq:u_1}$$
\end{document}

• Thanks a lot, brilliant answer and kind of an instant one too. I just wish these simple alignment jobs I am always struggling to pull of wouldn't require so much effort to complete. – whiterock Jan 28 '16 at 16:24
• By the way, you could save some typing with ^235_92Uinstead of ^{235}_{92}Uand ->[{...}]instead of ->[\text{...}], but that's down to personal preference. – mhchem Jan 28 '16 at 21:00
• @whiterock you're welcome. Yes, sometimes this is a bit of work, but actually, I was surprised how simple it was regarding the alignment operator inside the \ce-command. @mhchem, to be honest, I did not take a look on the chem part, I introduced your short style to my answer. Thank you. – LaRiFaRi Jan 29 '16 at 9:46
• @mhchem Thank you, did not know that - fantastic to get a response directly from the creators. – whiterock Jan 29 '16 at 9:51