Final answer:
The atomic number of fluorine is 9, reflecting the number of protons in its nucleus, a characteristic which defines the element. The mass number of the specified fluorine isotope is 19, combining its 9 protons and 10 neutrons. Isotopes have the same atomic number but different mass numbers due to varying numbers of neutrons.
Step-by-step explanation:
Atomic Number and Mass Number Explained
The atomic number of an element is defined by the number of protons in its nucleus. For fluorine, the atomic number is always 9 since it contains 9 protons, regardless of the isotope in question. This is what defines it as the element fluorine. The number of electrons in a neutral atom is also 9, to balance the positive charge of the protons.
The mass number of an isotope combines the number of protons and neutrons in an atom's nucleus. In this case, a fluorine isotope with 9 protons and 10 neutrons would have a mass number of 19 (9 protons + 10 neutrons = 19). Therefore, a normal, or most commonly occurring atom of fluorine also has a mass number of 19.
Defining Isotopes
Isotopes are forms of the same element with the same number of protons (and hence the same atomic number) but different numbers of neutrons, resulting in different mass numbers. For the given fluorine isotope, with 9 protons and 10 neutrons, the isotope’s mass number is 19.
To determine the number of neutrons in an atom, you subtract the atomic number from the mass number. For example, an isotope of uranium with an atomic number of 92 and a mass number of 235 has 235 - 92 = 143 neutrons.