The Nuclear Atom

Key Definitions

• Atomic Mass Unit (amu):

  • Unit of measurement for atomic mass;

  • 1 amu = 1 dalton (Da).

• Proton:

  • Positively charged particle in the nucleus;

  • Mass = 1 amu.

• Neutron:

  • Uncharged particle in the nucleus;

  • Mass = 1 amu.

• Electron:

  • Negatively charged particle outside the nucleus;

  • Mass < 1 amu.

Atomic Structure and the Periodic Table

• Atomic Number (Z):

  • For oxygen, Z = 8 (number of protons).

  • Determining an atom's identity: 8 protons = oxygen atom.

• Atomic Weight:

  • = Number of protons + Number of neutrons;

  • Average of isotopes (15.9994 for oxygen).

Isotopes

• Atoms of the same element with different neutron counts:

  • Example: Carbon-12 (6 protons, 6 neutrons) vs. Carbon-14 (6 protons, 8 neutrons).

Electron Configuration

• Number of electrons determined by atom's charge:

  • Atoms with differing electron counts are ions;

  • Proton charge = +1; Electron charge = -1.

  • Example: Chlorine atom with -1 charge has 18 electrons (17 protons + 1 extra electron).

Notation Summary

• Atomic Number: Number of protons (unchanging for an element).

• Atomic Weight: Number of protons + number of neutrons.

• Charge Number: Number of protons - number of electrons.

Example Notation

• Oxygen: 16 2- - O

• Neon: 20 8 107 Ne

• Sodium: 10 23 Na +