Final answer:
The atom in question is an isotope of nitrogen with the symbol 14N7, having 7 protons and 8 neutrons, which gives it a mass number of 22.
Step-by-step explanation:
An atom that has half as many protons as an atom of 28Si would have 14 protons because Silicon (Si) has 28 protons. Therefore, this atom is an isotope of nitrogen (14N).
Nitrogen's atomic number is 7, which is half of silicon's atomic number. Moreover, if this nitrogen atom has six fewer neutrons than an atom of 28Si, which has 14 neutrons (28 - 14 protons of Si), our nitrogen atom would have 8 neutrons (14 - 6).
The mass number of this nitrogen isotope would be the sum of its protons and neutrons, which is 14 + 8 = 22. Therefore, the symbol for this atom, including the atomic number and the mass number, is 14N7.