Style last post in loop differently?

How to add different class in last child of loop in wordpress.



<ul class="categories_list cat_main">
<?php  
$args=array('posts_per_page' => 6,'post_type' => 'post','orderby' => 'meta_value', 'meta_key' => 'views','order'=> 'DESC', 'post_status' => 'publish');
$the_query = new WP_Query($args);
$counter=1;
while ($the_query->have_posts()) : $the_query->the_post();?>  
      <li <?php if($counter==6){echo "class='last'";}?>>
      <div id="normal">
      <a href="<?php the_permalink(); ?>">
      <?php $values = get_post_custom_values("Featured Image");  ?>
      <img src="<?php echo $values[0];?>" /></a>
      </div>
      <?php /*?><div id="mob">
      <?php $values_m = get_post_custom_values("mobile Link");  ?><a href="<?php echo $values_m[0];?>">
      <?php $values = get_post_custom_values("Featured Image");  ?>
      <img src="<?php echo $values[0];?>" /></a>
      </div><?php */?>
      <p class="title"><a href="<?php the_permalink(); ?>">
        <?php the_title(); ?>
        </a></p>
      <?php /*?><p class="mob_title"><?php $values_m = get_post_custom_values("mobile Link");  ?><a href="<?php echo $values_m[0];?>">
        <?php the_title(); ?>
        </a></p><?php */?>
      <p>
        <?php $values1 = get_post_custom_values("views");?>
        <?php comments_popup_link('No Comments', '1 Comment', '% Comments'); ?>
        |
        <?php if(function_exists('the_views')) { the_views(); } ?>
      </p>
    </li>
    <?php $counter++; ?>
     <?php endwhile; ?>
    <?php wp_reset_query(); ?>
  </ul>


Thanks.