An atom has 17 protons, 18 neutrons, and 17 electrons. What is its mass number?

The correct answer is 35.

Key Points

• The mass number of an atom is calculated by summing the number of protons and neutrons in its nucleus.
• In this case, the atom has 17 protons and 18 neutrons.
• The formula for the mass number (A) is A = Number of Protons + Number of Neutrons.
• Therefore, the mass number of this atom is 17 + 18 = 35.

Additional Information

• Atomic Number
  • The atomic number is the number of protons in the nucleus of an atom.
  • It determines the chemical properties of an element and its place in the periodic table.
  • For this atom, the atomic number is 17, indicating it is chlorine (Cl).
• Isotopes
  • Isotopes are variants of a particular chemical element that have different numbers of neutrons.
  • Chlorine has two stable isotopes: Cl-35 and Cl-37.
  • Isotopes have the same atomic number but different mass numbers.
• Neutrons
  • Neutrons are neutral particles found in the nucleus of an atom.
  • They contribute to the mass of the atom but do not affect its chemical properties.
  • The number of neutrons in this atom is 18.
• Electrons
  • Electrons are negatively charged particles orbiting the nucleus of an atom.
  • In a neutral atom, the number of electrons equals the number of protons.
  • For this atom, there are 17 electrons.