tabularx from org to latex not recognized

["vendo.libri@libero.it" <vendo.libri@libero.it>]

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Hello Org-mode users' group, 
I'm having trouble with tables, in particular with trying to get Org-mode to understand the attributes in #+ATTR_LATEX. I have a 7x3 (rows x columns) table that has lots of text in the 2 column. This means I can't properly see the table if Emacs' window is reduced rather than in full-screen view. The rows and column are all jumbled up. I've read in the Org online manual (section 3.2) that you must type something like <n> where n is an integer so that the column restricts the number of visible characters in an otherwise overflowing text. I've tried it by placing <10> in the header of the column but it doesn't work. Can someone help me out? 
Furthermore, when I try to get the pdf via LaTeX export (C-c C-e l o), in spite of adding the necessary package to #+LATEX_HEADER and to the add-to-alist within the .emac configuration file, the table gets exported in a "tabular" environment instead of "tabularx" which allows for adaptable columns. In LaTeX it should be:
\begin{table}[htb]  \centering  \begin{tabularx}{\textwidth}{lXX}\toprule    NAME &amp; CHARACTERISTICS &amp; EXAMPLES\\[...]
I've read extensively sec.12.7.5 of the org-manual but I don't know how to get {\textwidth}{lXX} for tabularx recognized by Org-mode. Can someone show me how, with an example specific to my case? 
Here's some of the preamble from my org file. I've since continued to type the document in LaTeX because the org-exported pdf had an overflowing table that I couldn't control. Can someone shed some light into all this matter, please?
#+TITLE: My Title#+AUTHOR: Me#+DATE: April 2016#+STARTUP: nolatexpreview align#+OPTIONS: toc:nil#+LATEX_CLASS: article#+LATEX_CLASS_OPTIONS: [a4paper,10pt]#+ATTR_LATEX: :booktabs :environment tabularx :width textwidth :align lXX[...]
#+LATEX_HEADER: \usepackage{tabularx,booktabs}
#+LATEX_HEADER: \setcounter{secnumdepth}{0}[...]

This is how the table appears if I use TAB to hop from one field to the other.
| NAME              | CHARACTERISTICS                                                                                                                                                                    | EXAMPLES                               ||-------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------|| Metals            | <10> metallic bonding: adjacent atoms share electrons in a non-directional way; opaque, shiny, electrically conductive, they reflect photons, light rays from the environment      | a metal pan                            |

Any help is highly appreciated. Thank you.

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