Make a simple Bubble

Open a new document with size as the image below

Create gradient and Find the color from white to light blue and in order to set the blue color more dominant.

Make a circle with the elliptical marquee tool (note: press SHIFT while you get a circle to its fully rounded)

Create a new layer and use the Brush tool with size 100

Its color with the brush tool before each side of the circle. And give the middle a little color though appear more realistic.

When plasticity is realistic, now press CTRL + A to duplicate layer circle. Then pull the line for the top to bottom to create a shadow.

Now set the layer Opacity just become 50% or 30%. Remove a half circle of the bottom.

In fact this is finish, but can make so great such as this.

Please try