Chemical Bonding and Ionic Bonding

Chemical Bonding

• A compound is a substance formed by two or more different elements combined chemically.
• Atoms combine to form compounds through attractive forces called chemical bonds.
• Octet Rule: Atoms tend to gain, lose, or share electrons to achieve a stable electron arrangement with eight electrons in their outermost energy level, like noble gases.
• Exceptions: Transition metals, hydrogen, lithium, and beryllium do not always follow the octet rule.
• Ion: A charged atom or group of atoms. Forming cations (positive) by losing electrons and anions (negative) by gaining electrons.

Ionic Bonding

• Definition: An ionic bond is the force of attraction between oppositely charged ions in a compound.
• Formation: Complete transfer of electrons from one atom to another.
• Metals of groups I and II tend to lose electrons, while non-metals of groups VI and VII tend to gain electrons.
• Ionic compounds are neutral, meaning the total positive charges equal the total negative charges.

Writing Formulas of Ionic Compounds

• Formula: Uses symbols to represent present atoms and numbers to show how many atoms of each element are present.
• Metals in groups I & II, with non-metals in groups VI & VII often form ionic compounds.
• Examples of polyatomic anions include: hydroxide, nitrate, hydrogen carbonate, permanganate, carbonate, chromate, dichromate, sulfate, sulfite, thiosulfate, phosphate, and ammonium.
• To write a formula, balance the positive and negative charges.

Covalent Bonding

• Definition: A molecule is a group of atoms joined together, capable of independent existence. Covalent bonds involve the sharing of electrons between atoms.
• Formation: Shared electron pairs hold atoms to together. Atoms share electrons to obtain a stable electron configuration.
• Sigma bond: Formed by head-on overlap of atomic orbitals.
• Pi bond: Formed by sideways overlap of atomic orbitals.
  • Single bond = 1 sigma
  • Double bond = 1 sigma, 1 pi
  • Triple bond = 1 sigma, 2 pi
• Examples: Hydrogen molecules, chlorine molecules, and water molecules.

Properties of Ionic and Covalent Compounds

• Ionic Compounds: High melting/boiling points, usually solids at room temperature, hard and brittle, conduct electricity when molten or dissolved in water.
• Covalent Compounds: Low melting and boiling points, usually liquids or gases at room temperature, soft often, not conduct electricity.

Electronegativity

• Definition: Electronegativity is an atom's ability to attract shared electrons in a covalent bond.
• Polar Covalent Bond: Unequal sharing of electrons, causing one end of the bond to be slightly positive (σ+) and the other slightly negative (σ-).
• Non-polar Covalent Bond: Equal sharing of electrons.
• Predicting Polarity: Larger electronegativity difference usually means a more polar bond.

Intermolecular Forces

• Intramolecular forces: Hold atoms together within a molecule (covalent or ionic bonds).
• Intermolecular forces: Forces of attraction between molecules. Weak forces compared to intramolecular forces.
  • Van der Waals forces: Weak attractive forces between non-polar molecules. Temporary dipoles arise from shifting electron distributions.
  • Dipole-dipole forces: Attractive forces between polar molecules.
  • Hydrogen bonds: Strong dipole-dipole forces between molecules when hydrogen is bonded to nitrogen, oxygen, or fluorine.

Chemical Equilibrium

• Definition: Chemical equilibrium is a dynamic state in a reversible reaction where the rates of the forward and reverse reactions are equal.
• Le Chatelier's Principle: If a stress is applied to a system at equilibrium, the system shifts to relieve the stress. The stress can include changes in concentration, pressure, or temperature.
• Equilibrium Constant (K): A constant that relates the concentrations of reactants and products at equilibrium.

Explore the fundamental concepts of chemical bonding, including how compounds form through attractive forces called chemical bonds. Learn about the octet rule and exceptions, as well as the definition and formation of ionic bonds, focusing on the transfer of electrons between atoms.