Inside the Atom

Cheat Sheet: Inside the Atom

Structure of the Atom

• Nucleus surrounded by electrons

• Most mass concentrated in the nucleus

• Volume is mostly empty space

• Involves protons, neutrons, and electrons

Subatomic Particles

• Proton: 1 amu, Positive charge, located in the nucleus

• Neutron: 1 amu, Neutral charge, located in the nucleus

• Electron: 1/2000 amu (very light), Negative charge, located in energy levels/orbits around nucleus

Atomic Mass and Number

• Mass Number: Sum of protons and neutrons

• Atomic Number: Number of protons (and electrons for neutral atoms)

  • Example: Iron (Fe), Atomic Number = 26 (26 protons and 26 electrons)

Calculating Neutrons

• Neutrons = Mass Number - Atomic Number

  • Example: Helium: Mass Number = 4, Atomic Number = 2, Neutrons = 2

Standard Atomic Notation

• Written as: [ Element^{Mass Number}_{Atomic Number} ]

  • Example: [ He^{4}_{2} ]

Valence Electrons

• Indicated by Group Number on periodic table

  • Example: Lithium (Li) in Group 1 has 1 valence electron

    • Determine for: Mg, Ca, S, Al, F, Ar

Electron Shells

• Period Number indicates how many energy levels/orbits the atom has

  • Example: Lithium is in Period 2 → 2 electron orbits.

Cheat Sheet: Inside the Atom

Structure of the Atom

• Nucleus surrounded by electrons

• Most mass concentrated in the nucleus

• Volume is mostly empty space

• Involves protons, neutrons, and electrons

Subatomic Particles

• Proton: 1 amu, Positive charge, located in the nucleus

• Neutron: 1 amu, Neutral charge, located in the nucleus

• Electron: 1/2000 amu (very light), Negative charge, located in energy levels/orbits around nucleus

Atomic Mass and Number

• Mass Number: Sum of protons and neutrons

• Atomic Number: Number of protons (and electrons for neutral atoms)

  • Example: Iron (Fe), Atomic Number = 26 (26 protons and 26 electrons)

Calculating Neutrons

• Neutrons = Mass Number - Atomic Number

  • Example: Helium: Mass Number = 4, Atomic Number = 2, Neutrons = 2

Standard Atomic Notation

• Written as: [ Element^{Mass Number}_{Atomic Number} ]

  • Example: [ He^{4}_{2} ]

Valence Electrons

• Indicated by Group Number on periodic table

  • Example: Lithium (Li) in Group 1 has 1 valence electron

    • Determine for: Mg, Ca, S, Al, F, Ar

Electron Shells

• Period Number indicates how many energy levels/orbits the atom has

  • Example: Lithium is in Period 2 → 2 electron orbits.