General Chemistry Exam Review: Atomic Structure, Periodic Table, Chemical Bonding, and Stoichiometry

Atomic Structure and Electron Configuration

Quantum Numbers and Electron Arrangement

Quantum numbers describe the properties and arrangement of electrons in atoms. They are essential for understanding atomic structure and electron configuration.

• Principal Quantum Number (n): Indicates the energy level or shell.

• Angular Momentum Quantum Number (l): Defines the subshell (s, p, d, f).

• Magnetic Quantum Number (ml): Specifies the orbital within a subshell.

• Spin Quantum Number (ms): Describes the spin direction of the electron (+1/2 or -1/2).

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

Hund's Rule: Electrons fill degenerate orbitals singly before pairing.

Aufbau Principle: Electrons occupy the lowest energy orbitals first.

Electron Configuration

Electron configuration shows the distribution of electrons among the orbitals of an atom.

• Example (Manganese, Mn):

$1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^5$

• Core Electrons: Electrons in inner shells, not involved in bonding.

• Valence Electrons: Electrons in the outermost shell, involved in chemical reactions.

• Example (Gallium, Ga): 28 core electrons, 3 valence electrons.

Lewis Dot Structures

Lewis dot structures represent valence electrons as dots around the chemical symbol.

• Example (Silicon, Si): 4 dots, representing 4 valence electrons.

The Periodic Table and Periodic Trends

Main-Group Elements and Blocks

The periodic table is divided into blocks based on electron configuration:

• Main-group elements: Found in the s and p blocks.

• Transition metals: Found in the d block.

• Inner transition metals: Found in the f block.

Element Classification

• Alkali metals: Group 1 elements.

• Alkaline earth metals: Group 2 elements.

• Halogens: Group 17 elements.

• Noble gases: Group 18 elements.

• Metalloids: Elements with properties intermediate between metals and nonmetals.

Periodic Trends

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

• Ionization Energy (IE): Energy required to remove an electron; increases across a period, decreases down a group.

• Effective Nuclear Charge (Zeff): The net positive charge experienced by valence electrons.

• Shielding Effect: Inner electrons shield outer electrons from the nucleus.

Example: Place N, F, As in order of increasing ionization energy: As < N < F.

Chemical Bonding

Covalent and Ionic Bonds

Chemical bonds form between atoms to achieve stability.

• Covalent Bond: Electrons are shared between atoms.

• Ionic Bond: Electrons are transferred from one atom to another.

• Double Covalent Bond: Two pairs of electrons are shared between atoms.

Paramagnetism and Diamagnetism

• Paramagnetic substances: Have unpaired electrons and are attracted to a magnetic field.

• Diamagnetic substances: All electrons are paired and are weakly repelled by a magnetic field.

Stoichiometry and Empirical/Molecular Formulas

Empirical and Molecular Formulas

The empirical formula shows the simplest whole-number ratio of atoms in a compound. The molecular formula shows the actual number of atoms in a molecule.

• Example: If a compound has a molar mass of 305.3 g/mol and an empirical formula of C2H5O2, its molecular formula is C8H20O8.

Percent Composition

Percent composition is the percentage by mass of each element in a compound.

• Formula:

$\text{Percent composition} = \frac{\text{mass of element in 1 mol of compound}}{\text{molar mass of compound}} \times 100\%$

Stoichiometric Calculations

Stoichiometry involves calculations based on the relationships between reactants and products in chemical reactions.

• Mole Concept: 1 mole = $6.022 \times 10^{23}$ particles.

• Example: Calculating oxygen atoms in 3.00 g of Na2Cr2O7 using molar mass.

Nomenclature and Compound Classification

Naming Compounds

• Binary Ionic Compounds: Name the cation first, then the anion.

• Molecular Compounds: Use prefixes to indicate the number of atoms.

• Example: IBr5 is named iodine pentabromide.

Compound Classification

• Organic Compounds: Contain carbon and hydrogen, often with oxygen or nitrogen.

• Inorganic Compounds: Do not primarily contain carbon-hydrogen bonds.

Tables

Sample Table: Quantum Numbers

The following table summarizes a set of quantum numbers and their meaning:

n	l	ml	ms
3	0	0	+1/2
2	0	0	+1/2
2	0	0	-1/2
1	0	0	+1/2
1	0	0	-1/2

Additional info:

• Some questions involve application of periodic trends, electron configuration, and chemical nomenclature, which are foundational topics in General Chemistry.

• Empirical and molecular formula calculations require knowledge of stoichiometry and percent composition.

• Paramagnetism and diamagnetism are discussed in the context of electron pairing and magnetic properties.