Compute the atomic density (the number of atoms per cm3 ... rather than the mass density g/cm3) for a perfect crystal of silicon at room temperature, given that the room temperature density and atomic weight of silicon are 2.33 g/cm3 and 28.09 g/mol, respectively.

Explanation:

You can convert the density into atomic density using the atomic weight and Avogadro's number

A dimensional analysis is very helpful:

Follow the chain: g cancels with g, mol cancels with mol; at the end, what remains is atoms/cm³, which is what you want.

Use that with your data:

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.