It seems like everyone has a little trick to chopping an onion without crying. People have told me that they wear sunglasses, chop the onion under water or light a candle and place it next to the chopping board. The best I ever heard was putting a piece of bread in your mouth while you slice and dice. 
Onions belong to a family of veggies that includes garlics, leeks and chives. One thing that makes this family unique is that they all absorb sulfur from the soil as they grow. Onions store that sulfur as an enzyme in the root (the hairy part at the end) and that’s the culprit for the waterworks. When you cut into the root, the released enzyme reacts with the vegetable’s flesh to create a gas that winds its way up toward your face. When the gas meets the water in your eyes, it turns into an acid, which irritates your eyeballs and makes you cry.
Don’t cry me a river
So, while I like the idea of cooking by candlelight, my method for tear-free chopping starts with two rules.
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Leave the root end intact as much as possible. The fewer enzymes that are released, the better. What’s more, the root helps hold the onion together when chopping.
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Always use a sharp knife. It not only allows you to work more quickly and efficiently (a bonus for prepping anything), but it also makes a clean slice. Dull knives bruise and crush the onion’s flesh, allowing more of that tearjerker gas into the air.
A proper chop
This simple technique is quick and easy and creates a painless dice every time.
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With the skin still on, cut the onion directly in half through the root.
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Place the flat surface down on the chopping board and slice off the pointy end. Leave the root end on and peel.
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Slice vertically along the length of the onion, coming as close to the root as possible without cutting into it. Push the onion flesh back together.
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Make a horizontal cut, half way down the onion, parallel to the chopping board. 
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With your fingers holding the root end, slice across your original cuts to create a dice. 
Easier done than said, for sure. Check out this video to watch a step-by-step demonstration. And practice your newfound skills with these healthy Turkey Burgers with Red Pepper Relish and Yogurt Sauce.