Introduction to Chemical Compounds and Bonding

Chapter 3: Compounds

Types of Bonds

Chemical bonds are the forces that hold atoms together in compounds. There are three primary types of chemical bonds: ionic, covalent, and metallic. Each type has distinct properties and forms under different conditions.

• Ionic Bonds: Formed by the attraction between positively charged ions (cations) and negatively charged ions (anions).

  • Ionic compounds are composed of ions.

  • Cations (+): Lose electrons; typically metals.

  • Anions (-): Gain electrons; typically nonmetals.

  • Example: Sodium chloride (NaCl) is formed when sodium (Na) loses an electron to become Na+, and chlorine (Cl) gains an electron to become Cl-.

• Covalent Bonds: Formed by the sharing of electron pairs between atoms.

  • Usually composed of nonmetals.

  • Atoms share electrons to achieve stable electron configurations.

  • Example: Water (H2O) is formed when hydrogen and oxygen share electrons.

• Metallic Bonding: Involves a 'sea of electrons' that move freely around metal cations.

  • Composed of metals.

  • Electrons are delocalized, allowing metals to conduct electricity and be malleable.

  • Example: Copper (Cu) metal exhibits metallic bonding.

Chemical Formulas

Writing Chemical Formulas

Chemical formulas represent the types and numbers of atoms or ions in a compound. The atomic symbol is used, and subscripts on the bottom right indicate the number of each atom or ion present (except when the number is one).

• Atomic Symbol: Represents the element (e.g., Na for sodium, Cl for chlorine).

• Subscripts: Indicate the number of atoms or ions (e.g., AlCl3 means one aluminum and three chlorine atoms).

• Example: The formula for aluminum chloride is AlCl3.

Forming Ionic Compounds

When writing formulas for ionic compounds, the total positive charge must balance the total negative charge so that the compound is electrically neutral. The subscripts are chosen to achieve this balance.

• Charge Balance: The sum of positive and negative charges must equal zero.

• Lowest Terms: Subscripts should be reduced to the lowest whole number ratio.

• Example:

  • Calcium ion (Ca2+) and nitride ion (N3-): $\text{Ca}^{2+} + \text{N}^{3-}$ To balance charges: 3 Ca2+ (total +6) and 2 N3- (total -6) $3 \times (+2) + 2 \times (-3) = 0$ Formula: Ca3N2

  • Name: Calcium nitride

• Example:

  • Sodium ion (Na+) and oxide ion (O2-): $2 \times (+1) + 1 \times (-2) = 0$ Formula: Na2O

  • Name: Sodium oxide

Naming Ionic Compounds

Ionic compounds are named by stating the cation name followed by the anion name. No prefixes are used for the subscripts, as there is only one possible combination for each pair of ions that results in a neutral compound.

• Cation Name: The name of the positive ion (usually a metal).

• Anion Name: The name of the negative ion (usually a nonmetal, often ending in "-ide").

• Example: CaS is named calcium sulfide.

Summary Table: Types of Chemical Bonds

Bond Type	Particles Involved	How Bond Forms	Typical Elements	Example
Ionic	Cations & Anions	Transfer of electrons	Metal + Nonmetal	NaCl
Covalent	Atoms	Sharing of electron pairs	Nonmetal + Nonmetal	H2O
Metallic	Metal cations & delocalized electrons	Sea of electrons	Metal + Metal	Cu (copper metal)

Key Equations

• Charge Balance Equation: $\sum \text{(cation charges)} + \sum \text{(anion charges)} = 0$

• General Formula for Ionic Compounds: $\text{A}_x\text{B}_y$ Where x and y are the smallest whole numbers that balance the charges of cation (A) and anion (B).

Additional info:

• In covalent compounds, prefixes (mono-, di-, tri-, etc.) are used to indicate the number of atoms, but not in ionic compounds.

• Polyatomic ions (e.g., SO42-, NH4+) follow similar rules for charge balance in formulas.