Answer:
Homogeneous mixtures mix completely but heterogeneous mixtures don't mix completely
There are 7 periods in the modern periodic table
The differences are <u>the number of neutrons</u> and the <u>atomic mass</u><u /><u />.
Copper-63 has an atomic mass of 63 amu, and has 34 neutrons.
Copper-65 has an atomic mass of 65 amu, and has 36 neutrons.