Hi Guys. Ice is a crystal structure – everything lines up, so it’s easier for light to pass through. Snow are crystals, but there are lots of individual crystals so they don’t line up. That’s a little oversimplified, but it’s the general idea.
As Drew said, the water molecules in ice are arranged in a regular crystal structure. This Lets light pass through without it being scattered, making it appear clear. Snow flakes although being made of water molecules also arranged in crystals, are very irregularly shaped and therefore the light passing through them is scattered in different directions as it passes through making them appear white.
It’s to do with the particle size – the crystals in snow are much bigger and there are many air bubbles so all of the light which hits is bounces off the crystals and is reflected. Since this happens across the spectrum the snow appears white. Ice is made up almost entirely of crystals without the air bubbles so the light can penetrate much further into it.
The others have got it right! Snow is made of ice crystals mixed with air molecules. The air gaps between crystals, along with the crystals’ beautiful and complex shapes, bounce the light beams around so much that all the wavelengths eventually get reflected out, giving snow a white color (white light is what we see as the sum of all the other visible wavelengths).
On the contrary, ice doesn’t have a lot of air. This allows light to pass through the highly ordered structure of ice with minimal reflection. Sometimes ice can appear blue however, like in glaciers, because it is so thick it absorbs the longer red wavelengths!