There is shade and then there is shade. The common hybrid Impatiens from Impatiens walleriana (the short pinkish or white ones) will flower well in 100% shade, but it should still be bright. In deep shade they will grow slowly and you'll get less flowers. I'm a bit further north than you but I find that the more sun they get the better the larger they grow and the better they flower. The only problem is that they need loads of water in the sun, so I put them where they only get morning sun and they do great with little help from me.

my son bought a house and is a newbie in the gardening category.
He has a lot of shade in the front of house due to a large oak tree.
He took a lot of bushes out & also his foundation needs plants,,, can you help?

In central texas I would give them a fair amount of shade, especially afternoon shade. However, impatiens still do better with a fair amount of bright light. If you are growing them in a very dark corner of the yard it can be a problem.

other issues affecting flowering in impatiens:
- lack of adequate fertilizer during intial seedling stages (impatiens need very little fertilizer, but still need to be fertilized as young seedlings)
- too much nitrogen and very little phosphorus/potassium
- plants recently pinched back (require 2-3 weeks to reflower)
- plants less than 8-10 weeks old
- plants grown in very damp/satuarated soil. Let them dry otu slightly between waterings (but not wilting) to promote flowering.