Nucleus:

• It is located at the center of the atom.

• Contains:

  • Protons: Positively charged particles.

  • Neutrons: Particles with no electrical charge.

• Holds nearly all the mass of the atom.

Electrons:

• Negatively charged particles.

• Much lighter than protons and neutrons.

• Exist in orbitals (regions of probability) surrounding the nucleus, not in fixed paths like planets.

Points:

• Atomic Number (Z):

  • The number of protons in an atom.

  • Defines the element (since all atoms of a specific element have the same number of protons).

• Mass Number (A):

  • The sum of protons and neutrons in the nucleus.

  • Represented as a superscript before the element symbol (e.g., Carbon-12: ¹²C).

Important Sizes:

• Nucleus: Tiny, about 10,000 times smaller than the atom itself.

• Atom: Mostly empty space, with electrons existing in a much larger region compared to the nucleus.