Molecular Structure and Types of Chemical Bonds

Diatomic Molecules

At room temperature, seven elements exist naturally as diatomic molecules, meaning each molecule contains two atoms. These elements are hydrogen (H2), nitrogen (N2), oxygen (O2), fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2). Diatomic molecules are important in understanding elemental forms and chemical reactions.

• Diatomic molecules are stable due to the sharing of electrons between two atoms.

• They are often gases or volatile substances at room temperature.

• Examples: O2 (oxygen gas), N2 (nitrogen gas).

Molecular Compounds

Compounds formed from non-metal elements often exist as small molecules linked by chemical bonds. Most organic compounds, which contain carbon-hydrogen (C-H) bonds, are molecular compounds.

• Covalent bonds hold the atoms together in molecular compounds.

• Examples include water (H2O), methane (CH4), and ethylene (C2H4).

Ions, Ionic Compounds, and the Periodic Table

Formation of Ions

Main-group metals tend to lose electrons to form cations (positively charged ions), while main-group nonmetals tend to gain electrons to form anions (negatively charged ions). The resulting ions have the same number of electrons as the nearest noble gas.

• Cations: Formed by metals losing electrons (e.g., Na+, Ca2+).

• Anions: Formed by nonmetals gaining electrons (e.g., Cl-, O2-).

• Ionic compounds are formed by the electrostatic attraction between cations and anions.

• Salts are ionic compounds that can dissolve in polar solvents like water.

Writing Formulas for Ionic Compounds

Ionic compounds are electrically neutral. The formula is determined by balancing the charges of the cation and anion:

• The charge on the cation becomes the subscript for the anion.

• The charge on the anion becomes the subscript for the cation.

• If subscripts are not in the lowest whole-number ratio, divide by the greatest common factor.

Example: Magnesium nitride: Mg2+ and N3- combine to form Mg3N2.

Common Ions

Many ions are frequently encountered in chemistry, including transition metals and polyatomic ions. Polyatomic ions are small charged molecules composed of multiple atoms.

• The total charge is indicated with a superscript (e.g., Al3+, CN-).

• Transition metals may have variable charges.

• Polyatomic ions include groups like sulfate (SO42-), nitrate (NO3-).

Chemical Nomenclature

Inorganic Nomenclature

Inorganic compounds are named according to systematic rules:

• Name the cation first. If it can have more than one charge, indicate the charge with Roman numerals.

• If the anion is an element, change its ending to -ide.

• If the anion is a polyatomic ion, use its specific name.

Example: CuS is copper(II) sulfide; Cu2S is copper(I) sulfide.

Oxyanion Nomenclature

Oxyanions are polyatomic ions containing oxygen. Their names depend on the number of oxygen atoms:

• Fewer oxygens: ends in -ite (e.g., NO2- is nitrite).

• More oxygens: ends in -ate (e.g., NO3- is nitrate).

• Prefixes hypo- (fewest oxygens) and per- (most oxygens) are used for series.

Acid Nomenclature

Acids are named based on the anion they contain:

• If the anion ends in -ide, the acid name is hydro- + root + ic acid (e.g., HCl is hydrochloric acid).

• If the anion ends in -ite, the acid name ends in ous acid (e.g., HClO2 is chlorous acid).

• If the anion ends in -ate, the acid name ends in ic acid (e.g., HClO3 is chloric acid).

Nomenclature of Binary Molecular Compounds

Binary molecular compounds are formed between two nonmetals. The element farther left or lower in the periodic table is named first. Prefixes indicate the number of atoms:

• Prefixes: mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-.

• The second element's name ends in -ide.

• If two vowels meet, one is often dropped for ease of pronunciation.

Nomenclature of Organic Compounds

Alkanes and Alcohols

Organic chemistry focuses on compounds containing carbon. The simplest hydrocarbons are alkanes, which have only single bonds. When a hydrogen atom is replaced by a functional group, such as -OH, the compound is named as an alcohol.

• Alkane names: meth- (1 C), eth- (2 C), prop- (3 C), etc.

• Alcohols end in -ol (e.g., methanol, ethanol).

Isomers

Isomers are molecules with the same chemical formula but different structures. The position of functional groups is indicated by numbers in the name.

• Example: 1-propanol and 2-propanol differ in the location of the -OH group.

Stoichiometry and Chemical Equations

Law of Conservation of Mass

Stoichiometry is the study of mass relationships in chemical reactions, based on the Law of Conservation of Mass, which states that matter is neither created nor destroyed in a chemical reaction.

• The total mass of reactants equals the total mass of products.

• All chemical equations must be balanced to reflect this law.

Chemical Equations

Chemical equations are concise representations of chemical reactions. They show reactants on the left and products on the right, separated by an arrow.

• Coefficients are used to balance equations.

• States of matter are indicated: (g) for gas, (l) for liquid, (s) for solid, (aq) for aqueous solution.

Balancing Chemical Equations

Coefficients are added to balance equations, ensuring the same number of each atom on both sides. Changing subscripts alters the identity and properties of the compound, while changing coefficients only changes the amount.

• Example:

• Example:

Key Equations and Concepts

• Law of Conservation of Mass:

• Balancing Ionic Compounds:

• Example Chemical Equation:

Additional info: These notes cover General Chemistry topics from chapters on atoms, molecules, ions, chemical reactions, stoichiometry, and nomenclature, suitable for college-level study.