Honors Chemistry Unit 1

Atoms, Molecules, and Ions

• Atoms are the smallest unit of matter.

• Atoms are composed of:

  • Protons (+ charge)

  • Neutrons (0 charge)

  • Electrons (- charge)

• Ions: Formed when atoms gain or lose electrons

  • Cations: Positive ions formed by losing electrons (+)

  • Anions: Negative ions formed by gaining electrons (-)

• Isotopes: Atoms of the same element with different numbers of neutrons, resulting in different mass numbers.

Mass Spectrometry

• Used to determine isotopic composition and atomic mass.

• Peaks in the mass spectrum represent different isotopes.

• The height of each peak indicates the relative abundance of the corresponding isotope.

• Average atomic mass is calculated using the formula: \text{Average atomic mass} = \sum{(\text{fractional abundance} \times \text{mass of isotope})}

Moles & Molar Mass

• 1 mole = 6.022 \times 10^{23} particles (Avogadro's number).

• Molar mass is the mass of 1 mole of a substance, expressed in grams per mole (g/mol).

• Molar mass can be found on the periodic table.

Electron Configuration

• Electron configuration follows:

  • Aufbau Principle: Electrons fill orbitals in order of increasing energy.

  • Pauli Exclusion Principle: No two electrons in the same atom can have the same set of four quantum numbers (each orbital can hold a maximum of two electrons with opposite spins).

  • Hund's Rule: Electrons individually occupy each orbital within a subshell before doubling up in any one orbital.

• Order of filling orbitals: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p…

• Core electrons: Inner shell electrons.

• Valence electrons: Outer shell electrons; responsible for the chemical behavior of an atom.

Periodic Trends

• Atomic radius:

  • Decreases from left to right across a period (→).

  • Increases from top to bottom down a group (↓).

• Ionization energy:

  • Increases from left to right across a period (→).

  • Decreases from top to bottom down a group (↓).

• Electronegativity:

  • Increases from left to right across a period (→).

  • Decreases from top to bottom down a group (↓).

• These trends are caused by:

  • Effective nuclear charge (Z_{eff}): The net positive charge experienced by an electron in an atom.

  • Shielding: The reduction of the effective nuclear charge on the outer electrons due to the presence of inner electrons.

Photoelectron Spectroscopy (PES)

• Measures the energy needed to remove electrons from atoms.

• X-axis represents binding energy.

• Y-axis represents the number of electrons.

• Peaks in the PES spectrum represent sublevels.

• Higher binding energy indicates that the electron is closer to the nucleus.