Atomic Structure, Bonding, and Molecular Shapes Explained

Electrical Conductivity in Solids

Metal atoms possess outer electrons that are not tied to any single atom. These free electrons can move freely within the metal's structure when an electric current is applied, making metals excellent conductors. In contrast, covalent or ionic solids lack such free electrons, preventing electron flow and making them non-conductors.

Electron Configuration Principles

Filling Electron Shells and Orbitals

To determine electron configuration, first fill all lower electron shells. Then, apply specific rules to place valence electrons into their proper shells. Hund's Rule is crucial: it states that electrons will singly occupy all orbitals within a subshell before any orbital is doubly occupied. The Pauli Exclusion Principle dictates that no two electrons in an atom can have the same set of four quantum numbers, meaning each orbital can hold a maximum of two electrons with opposite spins. While fundamental, it doesn't directly dictate the order of filling like Hund's Rule.

For oxygen, with an atomic number of 8, there are 8 electrons. The electron configuration is thus 1s² 2s² 2p⁴. The four electrons in the 2p subshell (with 3 available orbitals) must be arranged with two electrons in one orbital and the other two placed singly in the remaining two orbitals, following Hund's Rule.

Common Electron Configurations

• [Ar] 4s²
• 1s² 2s² 2p⁶ 3s² 3p⁶

Understanding Quantum Numbers

• L=0 (s orbital)
• ml = -3, -2, -1, 0, 1, 2, 3 (f orbital)

Types of Chemical Bonds and Forces

Covalent Bond Characteristics

Covalent bonds between atoms can be single (two electrons shared), double (four electrons shared), or triple (six electrons shared). The more electrons shared between two atoms, the stronger their bond. For instance, a triple bond, like that found in nitrogen gas (N₂), requires a significant amount of energy to break. For diatomic elements like nitrogen gas, the bond type often corresponds to the number of electrons (up to three) needed to complete each atom's outer valence shell.

Other Intermolecular Forces and Bond Types

• Hydrogen bonds
• Ionic bonds
• Metallic bonds
• London Dispersion Forces

Molecular Geometry and Shapes

Common Molecular Geometries

• Tetrahedral
• Trigonal Planar
• Trigonal Pyramidal

For molecules with 2 bonded atoms + 2 lone pairs, the geometry is Bent.

Ionization Energy and Electron Removal

To determine which electron requires the most energy for its removal, we must consider the forces acting upon it. Repulsive forces, originating from quantum mechanics, prevent an electron from collapsing into the nucleus and are responsible for the discrete energy levels in atoms. However, it is the attractive forces that must be overcome; these are purely electrostatic, arising from the opposite charges of the positively charged nucleus and the negatively charged electron.

An electron in a lower energy level is both closer to the nucleus and experiences less shielding from other electrons. The former (proximity to nucleus) is important because the electrostatic force between two charged particles is inversely proportional to the square of the distance (1/r²) between them. The latter (electron shielding) is important because the negative charges of inner electrons shield (or partially cancel out) the positive charge of the nucleus, reducing the effective nuclear charge experienced by outer electrons.