Atomic Structure and Isotopes

Subatomic Particles and Isotope Notation

Atoms are composed of three main subatomic particles: protons, neutrons, and electrons. The number of protons defines the atomic number and the element. Isotopes are atoms of the same element with different numbers of neutrons.

• Proton (p+): Positively charged particle found in the nucleus.

• Neutron (n0): Neutral particle found in the nucleus.

• Electron (e-): Negatively charged particle found in orbitals around the nucleus.

Isotope notation: AZX, where A = mass number (protons + neutrons), Z = atomic number (protons), X = element symbol.

• Atoms are electrically neutral, so the number of protons equals the number of electrons.

• Ions have unequal numbers of protons and electrons.

Atomic Number, Mass Number, and Charge

• Atomic Number (Z): Number of protons in the nucleus.

• Mass Number (A): Total number of protons and neutrons.

• Charge of Atom: Atoms are neutral; ions have a net charge.

• Charge of Nucleus: Equal to the number of protons (positive charge).

Ions and Isotopes

Ion Table: Protons, Neutrons, and Electrons

Ions are atoms or molecules with a net electric charge due to the loss or gain of electrons.

Average Atomic Mass

The average atomic mass of an element is calculated using the masses and relative abundances of its isotopes:

Example (Chlorine):

• Isotopes: 35Cl (75.53%), 37Cl (24.47%)

• Calculation: amu

Mole Concept and Molar Mass

Avogadro's Number and Moles

The mole is a counting unit in chemistry. One mole contains Avogadro's number () of particles (atoms, molecules, ions).

• Molar Mass: The mass of one mole of a substance, in grams per mole (g/mol).

• Example: Molar mass of SO3: g/mol

Stoichiometry: Mass, Moles, and Atoms

• Converting grams to moles:

• Converting moles to atoms:

• Example: How many grams of gold in 15.3 moles?

Quantum Numbers and Electron Configuration

Quantum Numbers

Quantum numbers describe the properties of atomic orbitals and the properties of electrons in orbitals.

• Principal quantum number (n): Energy level (n = 1, 2, 3, ...)

• Angular momentum quantum number (l): Subshell (l = 0 to n-1; s, p, d, f)

• Magnetic quantum number (ml): Orientation (-l to +l)

• Spin quantum number (ms): Spin (+1/2 or -1/2)

Pauli Exclusion Principle: No two electrons in an atom can have the same set of four quantum numbers.

Electron Configuration and Subshells

• Maximum electrons in a subshell:

• Example: f-subshell (l=3) can hold 14 electrons.

• Impossible configurations: For example, 2d5 is not possible because d orbitals start at n=3.

Light, Energy, and Atomic Spectra

Electromagnetic Radiation and Energy Calculations

• Speed of light: m/s

• Relationship: (wavelength × frequency)

• Energy of a photon:

• Planck's constant: J·s

Example: Calculate the energy of a photon with frequency Hz:

Bohr Model and Hydrogen Atom Transitions

• Energy levels: J

• Energy change for transitions: J

• Wavelength of emitted/absorbed light:

Example: Calculate the wavelength for a transition from n=4 to n=1 in hydrogen:

J

de Broglie Wavelength

• de Broglie equation:

• Example: For a 2.9 g Ping-Pong ball at 27 mph, m

Periodic Trends

Ionization Energy

Ionization energy is the energy required to remove an electron from a gaseous atom or ion.

• Trends: Increases across a period (left to right), decreases down a group.

• Explanation: Electrons closer to the nucleus are held more tightly (less shielding).

Large jumps in ionization energy indicate removal of a core (non-valence) electron.

Isoelectronic Species

Isoelectronic species have the same number of electrons but different nuclear charges.

• Example: F- and Na+ are isoelectronic (10 electrons each).

Summary Table: Key Formulas

Additional info:

• Some explanations and context were expanded for clarity and completeness.

• Tables were reconstructed and formulas were provided in standard LaTeX format.