General Chemistry Study Guide: Atomic Structure, Bonding, Molecular Geometry, and Chemical Quantities

Atomic Structure and Periodic Properties

Electronegativity and Ionization Energy

Electronegativity is a measure of an atom's ability to attract electrons in a chemical bond. Ionization energy is the energy required to remove an electron from a gaseous atom.

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

• Ionization Energy Trend: Increases across a period, decreases down a group.

• Example: Order of increasing electronegativity: Na < S < Cl < F

• Atomic Radius: Decreases across a period, increases down a group.

• Shielding Effect: Inner electrons shield outer electrons from the nucleus, reducing effective nuclear charge.

Electron Configuration and Shielding

Electron configuration describes the arrangement of electrons in an atom. Shielding refers to the reduction in effective nuclear charge on the electron cloud due to inner electrons.

• Valence Electrons: Electrons in the outermost shell, involved in bonding.

• Shielding: Electrons in lower energy levels shield valence electrons from the nucleus.

• Example: In Se, the 4p electrons are most shielded from nuclear charge.

Chemical Bonding and Hybridization

Hybridization

Hybridization is the mixing of atomic orbitals to form new hybrid orbitals suitable for bonding.

• sp Hybridization: Linear geometry, 180° bond angle.

• sp2 Hybridization: Trigonal planar geometry, 120° bond angle.

• sp3 Hybridization: Tetrahedral geometry, 109.5° bond angle.

• Example: The central atom in CH2O is sp2 hybridized.

Ionic and Covalent Bonds

Ionic bonds form between metals and nonmetals through electron transfer. Covalent bonds form between nonmetals by sharing electrons.

• Ionic Compound: NaCl is an example of an ionic compound.

• Covalent Compound: H2O is an example of a covalent compound.

• Polarity: Molecules with unequal sharing of electrons are polar (e.g., H2O).

Molecular Geometry and Electron Domain Geometry

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory predicts the shapes of molecules based on electron pair repulsion.

• Electron Domain Geometries:

  • Linear: 2 domains

  • Trigonal Planar: 3 domains

  • Tetrahedral: 4 domains

  • Trigonal Bipyramidal: 5 domains

  • Octahedral: 6 domains

• Molecular Geometry: Determined by the number of bonding and lone pairs.

• Example: SF4 has a seesaw molecular geometry.

Lewis Structures

Lewis structures represent the arrangement of electrons in a molecule, showing bonds and lone pairs.

• Steps to Draw Lewis Structures:

  1. Count total valence electrons.

  2. Arrange atoms and connect with single bonds.

  3. Distribute remaining electrons as lone pairs.

  4. Check for octet rule and formal charges.

• Formal Charge Formula: $\text{Formal Charge} = \text{Valence electrons} - (\text{Nonbonding electrons} + \frac{1}{2}\text{Bonding electrons})$

• Example: For Br in perbromate ion, calculate formal charge using the above formula.

Chemical Quantities and Empirical Formulas

Mole Calculations

The mole is a fundamental unit in chemistry for counting particles. Molar mass is used to convert between grams and moles.

• Mole Formula: $\text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}$

• Example: Calculate grams in 8.324 mol of vitamin B6, C8H11NO3P.

Empirical Formula Determination

The empirical formula is the simplest whole-number ratio of atoms in a compound.

• Steps:

  1. Convert mass of each element to moles.

  2. Divide by the smallest number of moles.

  3. Multiply to get whole numbers if necessary.

• Example: A sample contains 4.48 g C, 0.84 g H, and 4.48 g O. Find the empirical formula.

Tables

Comparison of Electron Domain Geometries

Electron Domains	Geometry	Bond Angle
2	Linear	180°
3	Trigonal Planar	120°
4	Tetrahedral	109.5°
5	Trigonal Bipyramidal	90°, 120°
6	Octahedral	90°

Common Hybridizations and Geometries

Hybridization	Geometry	Example
sp	Linear	CO2
sp2	Trigonal Planar	BF3
sp3	Tetrahedral	CH4

Additional info:

• Questions also cover formal charge, expanded octets, and molecular polarity, which are essential for understanding molecular structure and reactivity.

• Some questions require drawing Lewis structures and calculating empirical formulas, integrating mathematical operations with chemical concepts.