Atomic Structure and Electron Configuration

Electron Subshells and Capacity

The arrangement of electrons in atoms is described by subshells (s, p, d, f), each with a specific capacity.

• p Subshell: Can hold a maximum of 6 electrons.

• Electron configuration: Follows the Aufbau principle, filling lower energy subshells first.

• Example: The p subshell in the second energy level (2p) can hold up to 6 electrons.

Equation:

For p subshell ():

Ions and Electron Count

An ion is an atom or molecule with a net electric charge due to the loss or gain of electrons.

• Cations: Positive ions formed by losing electrons.

• Anions: Negative ions formed by gaining electrons.

• Example: An atom with 17 protons and 18 electrons is a chloride ion ().

Valence Electrons

Valence electrons are the electrons in the outermost shell, crucial for chemical bonding.

• Nitrogen: Has 5 valence electrons (group 15 element).

• Determination: Group number for main group elements indicates valence electrons.

Chemical Bonding

Bond Polarity

Bond polarity arises from differences in electronegativity between bonded atoms.

• Most polar bond: O-H bond, due to large electronegativity difference between O and H.

• Polarity order: Greater difference in electronegativity = more polar bond.

Types of Chemical Bonds

• Ionic Bonds: Formed between metals and nonmetals (e.g., Na and F).

• Covalent Bonds: Shared electrons between nonmetals.

• Polar Covalent: Unequal sharing of electrons.

• Metallic Bonds: Delocalized electrons among metal atoms.

• Example: NaF is an ionic compound.

Octet Rule Exceptions

Most atoms aim for 8 electrons in their valence shell, but some molecules violate this rule.

• BF3: Boron has only 6 valence electrons in this molecule.

• Other exceptions: Molecules with odd numbers of electrons, or expanded octets (period 3 and beyond).

Oxidation Numbers and Redox Reactions

Oxidation Number Assignment

Oxidation numbers indicate the charge an atom would have if electrons were transferred completely.

• Mn in MnO2: Oxygen is -2, total for two oxygens is -4. Mn must be +4.

• Equation:

Redox Reactions

• Reduction: Gain of electrons.

• Oxidation: Loss of electrons.

• Species reduced: Gains electrons.

Nomenclature and Compound Naming

Transition Metal Compounds

Transition metals can have multiple oxidation states, indicated by Roman numerals in compound names.

• Fe2(SO4)3: Iron(III) sulfate.

• Systematic naming: Metal (oxidation state) + anion name.

Molecular Compounds

• Dinitrogen tetroxide: N2O4

• Prefix system: Used for nonmetal compounds (di-, tri-, tetra-, etc.).

Formal Charge and Molecular Geometry

Formal Charge Calculation

Formal charge helps determine the most stable Lewis structure.

• Formula:

• NH4+: Nitrogen has a formal charge of +1.

Molecular Geometry

The shape of a molecule is determined by the arrangement of electron pairs around the central atom.

• SO3: Trigonal planar geometry.

• VSEPR Theory: Predicts molecular shapes based on electron pair repulsion.

Electrostatic Potential Maps

Electron Density Regions

Electrostatic potential maps show regions of high and low electron density in molecules.

• Highest electron density: Most negative region (often colored red or dark).

• Lowest electron density: Most positive region (often colored blue or light).

Summary Table: Key Concepts