Sorting through div class via opacity

So I'm using classes to sort different content, but I'm not actually sure how to apply this sorting.

    <div class="class1"><div class="heads">Title</a></div>
<div class="description"><p>Class 1 Item 1</p></div></div>

<div class="class2"><div class="heads">Title</a></div>
<div class="description"><p>Class 2 Item 1</p></div></div>

<div class="class2"><div class="heads">Title</a></div>
<div class="description"><p>Class 2 Item 2</p></div></div>

<div class="class3"><div class="heads">Title</a></div>
<div class="description"><p>Class 3 Item 1</p></div></div>

So let's say the user clicks a button that says 'Class 2'. I want the opacity of everything that is not class 2 to be, say, .5 while class 2's opacity stays at 1. I've tried using .not(), but I'm not familiar with it and most examples use it in conjunction with .siblings(), and I don't want the siblings to fade either. Help? I'm not sure what to do.