Understanding Atomic Structure and Isotopes

Key Concepts

• Atomic Number

  • Represents the number of protons in an atom.
  • Denoted by the smaller number in an element symbol.
  • For example, in sodium (Na), the atomic number is 11.
  • All atoms of a particular element have the same number of protons.

• Mass Number

  • Represents the total number of protons and neutrons in an atom.
  • Denoted by the larger number in an element symbol.
  • Calculation: Mass number = Protons + Neutrons.
  • Example: Sodium has a mass number of 23, meaning it has 12 neutrons (23 - 11 = 12).

• Electrons

  • In a neutral atom, the number of electrons equals the number of protons.
  • Electrons have a negative charge, canceling out the positive charge of protons, leading to no overall charge.

Isotopes

• Definition: Atoms of the same element with different numbers of neutrons.
  • Same atomic number but different mass numbers.
  • Example: Two isotopes of sodium — both have 11 protons (atomic number), but one has 12 neutrons and the other 13 neutrons.
  • Some isotopes are radioactive.

Ions

• Definition: Atoms that have gained or lost electrons and thus have a net charge.
  • Positive Ions (Cations): Formed by losing electrons.
    • Example: A sodium atom loses one electron, resulting in a sodium ion with a +1 charge (11 protons, 10 electrons).
  • Note: Losing two electrons results in a 2+ charge.

Conclusion

• Using atomic and mass numbers, you can determine the number of protons, neutrons, and electrons in atoms.
• Isotopes and ions reflect changes in neutrons and electrons, respectively.

Additional Resources

• For further practice, refer to the questions in the revision workbook linked in the lesson.