How are exoplanets different from the planets in our solar system?

Exoplanets are planets that orbit other stars. ... Exoplanets seem to follow the same general rules as the planets in our solar system: Small planets are rocky, big planets are gassy, and the ones in between may be watery. There are other rocky worlds orbiting stars at the right distance to allow liquid water to exist.

increased stability in the completion of fluorine's outer shell.

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.