Module #4

Introduction to Bonding

Chemical bonding is a fundamental concept in chemistry that describes the attractive forces that hold atoms together in compounds. It primarily involves the valence electrons, which are the electrons located in the outermost shell of an atom. There are two primary types of chemical bonds: ionic bonds and covalent bonds.

Ionic Compounds and Their Naming

Definitions

Ionic compounds are formed when one atom transfers electrons to another atom, resulting in the formation of charged ions that attract each other due to electrostatic forces. The naming of ionic compounds is based on the cation (positive ion) and anion (negative ion) they contain.

Example of Naming

For example, sodium chloride (NaCl) consists of sodium ions (Na⁺) and chloride ions (Cl⁻).

Chemical Formulas

Definition and Types

A chemical formula provides the chemical composition of a substance, indicating what elements it contains and in what proportions.

• Monatomic molecules: Helium (He), Gold (Au), Sodium (Na)

• Diatomic molecules: Oxygen (O2), Hydrogen (H2), Chlorine (Cl2)

• Polyatomic molecules: Ozone (O3), Sulfur (S4), Phosphorus (P8)

• Compounds: Water (H2O), Acetone (CH3COCH3)Compounds consist of two or more elements in fixed proportions.

Compound Examples

• Hydrochloric Acid (HCl): Contains 1 hydrogen atom and 1 chlorine atom.

• Water (H2O): Composed of 2 hydrogen atoms and 1 oxygen atom.

• Ammonia (NH3): Includes 1 nitrogen atom and 3 hydrogen atoms.

• Propane (C3H8): Consists of 3 carbon atoms and 8 hydrogen atoms.

• Calcium Hydroxide (Ca(OH)2): Contains 1 calcium atom, 2 oxygen atoms, and 2 hydrogen atoms.

Law of Definite Proportions

This law states that a chemical compound will always contain its component elements in fixed ratio by mass. This principle establishes that molecules having the same number and type of atoms, arranged in the same way, are those of the same compound.

Naming Ionic Compounds

Importance of Memorization

It is essential to memorize the names and formulas of common ionic compounds. For example, the formula for nitric acid is HNO3, and for sulfur trioxide, it is SO3.

Example Exercises

1. What is the name of FeBr3? – Iron(III) bromide

2. What is the charge on the sulfite ion? – SO3²⁻

More on Ionic Compounds

Naming Rules

• When naming binary ionic compounds (formed from a metal and a nonmetal), name the cation first, followed by the anion, adjusting the suffix to 'ide.'

  • Example: LiBr is lithium bromide, while MgCl2 is magnesium chloride.

• For metals with more than one oxidation state, Roman numerals in parentheses are used to indicate the charge on the metal ion (modern nomenclature).

Transition Metals

Many transition metals can have multiple oxidation states, hence require proper identification during naming.

Lewis Dot Structures

Application in Chemical Bonding

Lewis dot structures visually represent valence electrons in atoms. These diagrams are useful in understanding how atoms bond to form compounds. Elements in the same periodic group tend to have similar Lewis structures due to the same number of valence electrons.

Formation of Ionic Compounds

Basic Principles

Ionic compounds form when cations (positive ions) and anions (negative ions) attract each other, resulting in stable compound formation. For instance:

• Common Formation Example: Sodium (Na) tends to lose an electron to become Na⁺, while chlorine (Cl) gains an electron to become Cl⁻, resulting in the formation of NaCl.

Coulomb’s Law in Ionic Compounds

Forces of Attraction

The strength of the ionic bond can be explained using Coulomb's Law, which states that the force of attraction between two charged particles is directly proportional to the product of the magnitudes of their charges and inversely proportional to the square of the distance between them.

Trends in Ionic Compounds

To predict the strength of ionic attractions within different compounds, consider the size of ions and their corresponding charges. Smaller ions with higher charges exhibit stronger interactions, fundamentally affecting the properties, including melting and boiling points.