How many atoms are in not a specific amount of it though.

The value converted to be 2.86*10^5 angstroms. Each aluminum atom is about 1.48 angstroms, so we can divide. Assuming that each aluminum atom is stacked directly on another one (which they aren't, but we can't measure without making this assumption), we come up with 1.93 * 10^5 atoms thick. Basically it's 1.93 * 10^5

Exothermic,  physical change after it is already baked

All the elements are arranged by melting points on the periodic table. in row they go from metals to gasses. in the row from sodium to argon, sodium is more reactive than the one on its right, magnesium.