Compounds and Chemical Bonding

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom. They play a crucial role in determining how atoms interact and bond with each other.

• Definition: Electrons in the highest energy level (outer shell) of an atom.

• Importance: Responsible for chemical bonding and reactivity.

• Example: Oxygen has 6 valence electrons.

Octet Rule

The octet rule states that atoms tend to gain, lose, or share electrons to achieve a full set of eight valence electrons, resembling the electron configuration of noble gases.

• Application: Explains why atoms form bonds.

• Exceptions: Hydrogen and helium aim for 2 electrons.

• Example: Sodium loses 1 electron to achieve an octet.

Ionic Charges

Ions are atoms or molecules that have gained or lost electrons, resulting in a net charge.

• Cations: Positively charged ions (lost electrons).

• Anions: Negatively charged ions (gained electrons).

• Example: ,

Ionic Compounds vs Covalent Compounds

Ionic compounds are formed from the electrostatic attraction between cations and anions, while covalent compounds are formed by sharing electrons between atoms.

• Ionic: Metal + Nonmetal, transfer of electrons.

• Covalent: Nonmetal + Nonmetal, sharing of electrons.

• Example: (ionic), (covalent)

Polyatomic Ions

Polyatomic ions are charged species composed of two or more atoms covalently bonded, acting as a single ion.

• Examples: (nitrate), (sulfate), (ammonium)

• Importance: Common in ionic compounds.

Ionic Formulas and Names

Formulas for ionic compounds are written by balancing the charges of the ions. Naming depends on whether the metal is a main block or transition metal.

• Main Block Metals: Use element name (e.g., sodium chloride).

• Transition Metals: Use Roman numerals for charge (e.g., iron(III) oxide).

• Formula Example:

Lewis Dot Symbols and Structures

Lewis dot symbols represent valence electrons as dots around the element symbol. Lewis structures show how atoms bond and share electrons.

• Dot Symbols: Visualize valence electrons.

• Structures: Show bonding and lone pairs.

• Example: Lewis structure

Shape and Wedge/Dash Notation

Molecular shape is determined by the arrangement of atoms and electron pairs. Wedge and dash notation shows 3D structure.

• Shapes: Linear, bent, trigonal planar, tetrahedral, etc.

• Wedge: Bond coming out of the plane.

• Dash: Bond going behind the plane.

Covalent Names and Formulas

Covalent compounds are named using prefixes to indicate the number of atoms. Formulas reflect the actual number of each atom.

• Prefixes: mono-, di-, tri-, tetra-, etc.

• Example: is carbon dioxide.

Bond Polarity and Electronegativity

Bond polarity arises from differences in electronegativity between atoms. Electronegativity is the tendency of an atom to attract electrons.

• Ionic: Large difference, electrons transferred.

• Polar Covalent: Moderate difference, electrons shared unequally.

• Nonpolar Covalent: Small or no difference, electrons shared equally.

• Example: is polar; is nonpolar.

Dipole and Molecule Polarity

A dipole is a separation of charge within a molecule. Molecule polarity depends on both bond polarity and molecular shape.

• Dipole Moment: Vector sum of individual bond dipoles.

• Polar Molecule: Has net dipole moment (e.g., ).

• Nonpolar Molecule: No net dipole (e.g., ).

Introduction to Organic Chemistry

What is Organic Chemistry?

Organic chemistry is the study of carbon-containing compounds, especially those with carbon-hydrogen bonds.

• Scope: Includes hydrocarbons and their derivatives.

• Importance: Basis for life, pharmaceuticals, plastics, etc.

Molecular, Condensed, Lewis, Skeletal, and Ball-and-Stick Models

Organic molecules can be represented in several ways:

• Molecular Formula: Shows number and type of atoms (e.g., ).

• Condensed Formula: Groups atoms (e.g., ).

• Lewis Structure: Shows bonds and lone pairs.

• Skeletal Structure: Lines represent bonds; vertices represent carbon atoms.

• Ball-and-Stick Model: 3D representation of atoms and bonds.

Hydrocarbon Functional Groups

Hydrocarbons are classified by their bonding and structure:

• Alkanes: Single bonds, saturated ().

• Alkenes: At least one double bond ().

• Alkynes: At least one triple bond ().

• Aromatic: Contains benzene ring.

Additional Functional Groups

Functional groups determine the chemical properties of organic molecules.

• Alcohol:

• Ether:

• Aldehyde:

• Ketone:

• Carboxylic Acid:

• Ester:

• Amide:

• Amine:

• Imine:

• Nitrile:

• Thiol:

Alkane Nomenclature and Structures

Alkanes are named based on the number of carbon atoms and their structure.

• Prefixes: meth-, eth-, prop-, but-, pent-, etc.

• Example: is butane.

Saturated vs Unsaturated Hydrocarbons

Saturated hydrocarbons contain only single bonds; unsaturated hydrocarbons contain double or triple bonds.

• Saturated: Alkanes.

• Unsaturated: Alkenes and alkynes.

Isomers

Isomers are compounds with the same molecular formula but different structures.

• Structural Isomers: Different connectivity.

• Conformational Isomers: Same connectivity, different rotation.

• Stereoisomers: Same connectivity, different spatial arrangement.

• Geometric Isomers: Different arrangement around a double bond (cis/trans).

• Enantiomers: Non-superimposable mirror images.

Chirality

A molecule is chiral if it cannot be superimposed on its mirror image. Chiral molecules often have a carbon atom bonded to four different groups.

• Chiral Center: Carbon with four distinct substituents.

• Importance: Enantiomers can have different biological activity.

Additional info: Academic context and examples were added to clarify and expand brief review points.