Asubstance composed of two or more elements in a fixed, definite proportion is
a. a homogeneous mixture.
b. a heterogeneous mixture.
c. a compound.
d. a solution.
e. an alloy.

Neils bohr believed that electrons orbited the nucleus in different energy levels, based on strong support from

When a spring is compressed, the energy changes from kinetic to potential. which best describes what is causing this change?

Sally is making a model of a magnesium atom with an atomic mass number of 24 for her chemistry class. she has foam balls for the protons, neutrons, and electrons. she has added 6 neutrons to her model so far. how many more neutrons does she need to add to complete her neutral atom of magnesium?