custom Whatsapp button

how can I add a whatsapp button using this code ?

[ Moderator note: code fixed. Please wrap code in the backtick character or use the code button. ]

<ul class="social_media">
<h5><?php _e( 'Compartelo', THEMEDOMAIN ); ?></h5>

<li>
									<a> <?php the_permalink()?>" title="Retweet">
										<img src="<?php echo get_stylesheet_directory_uri(); ?>/images/social_black/twitter.png" alt=""/>
									</a>
								</li>
<li>
									<a>&title=<?php the_title()?>" title="Digg it">
										<img src="<?php echo get_stylesheet_directory_uri(); ?>/images/social_black/digg.png" alt=""/>
									</a>
								</li>
<li>
									<a>&t=<?php the_title()?>" title="social_black to Facebook">
										<img src="<?php echo get_stylesheet_directory_uri(); ?>/images/social_black/facebook.png" alt=""/>
									</a>
								</li>
<li>
									<a>&title=<?php the_title()?>&annotation=" title="Google Bookmark">
										<img src="<?php echo get_stylesheet_directory_uri(); ?>/images/social_black/google.png" alt=""/>
									</a>
								</li>
<li>
									<a>" title="RSS">
										<img src="<?php echo get_stylesheet_directory_uri(); ?>/images/social_black/rss.png" alt=""/>
									</a>
								</li>

also, i want to make sure it only shows on mobile.

https://wordpress.org/plugins/whatsapp/