What are the differences?

Seeds and nuts are not legumes, however, peas, beans and lentils are legumes. Some confusion may arise because legumes, which form pods, sometimes have the fruit in those pods referred to as seeds. Either the term fruit or seed may cause confusion. Nuts come in shells, and although the distinction between a shell and a pod may seem trifling, nuts definitely are not produced by leguminous plants. Seeds may or may not refer to the products of leguminous plants. The very small seeds of some grasses, however, are collectively known as millet, and are properly described as grain.

Basically i agree with you, although i would not include seeds and nuts under the rubric legumes.

I'm not a scientist, but isn't it possible that some legumes can form alkaline and acid?