Answer:
Compound Element
Definition: A compound contains atoms of different elements chemically combined together in a fixed ratio.
Definition: An element is a pure chemical substance made of same type of atom.
Elements and compounds are purely homogeneous substances and they have a constant composition throughout. Elements and compounds cannot be separated into their respective constituents by physical means. Compounds and mixtures are made up of different elements or different atoms.
Hopefully this helps you!!!!
Yes they are stable because they follow octet rule but am not sure if they are exist separetly
Answer:
Density of the He atom = 12.69 g/cm³
Explanation:
From the information given:
Since 1 mole of an atom = 6.022x 10²³ atoms)
1 atom of He = 
The volume can be determined as folows:
since the diameter of the He atom is approximately 0.10 nm
the radius of the He = 
= 0.05 nm
Converting it into cm, we have:
Assuming that it is a sphere, the volume of a sphere is
= 
= 
= 
Finally, the density can be calcuated by using the formula :
D = 12.69 g/cm³
Density of the He atom = 12.69 g/cm³
Ok so, remember that t<span>he average atomic mass is what is seen on the periodic table. It is the average mass of all of the isotopes with their frequency taken into account. What you need to do is add the products of the masses and frequencies Just like this:</span>
<span>0.903*267.8 + 0.097*270.9
When you add it the result is what you are looking for</span>
