CH5

Physical Properties of Ionic Compounds

• High melting points
• Hard and rigid
• Brittle
• Conductive (sometimes)
• Conductivity and brittleness come from the atomic-scale arrangement of atoms
• High melting and boiling points due to extremely high bond strength

Covalent Bond (Non-polar)

• A chemical bond in which two or more electrons are shared by two nonmetal atoms
• Electrons are equally shared (same elements)
• Example: H2 (Hydrogen molecule)
• Sharing electrons fulfills the octet rule

Covalent Bonding

• Single bond: two atoms share one pair of electrons (2 electrons)
• Double bond: two atoms share two pairs of electrons (4 electrons)
• Triple bond: two atoms share three pairs of electrons (6 electrons)
• Triple bonds are shorter and stronger than single bonds

Lewis Dot Structures

• Represent electrons as dots around the atomic symbol
• Same column = same dot structure
• Dots represent valence electrons
• Octet Rule: an atom is stabilized by having its valence energy level filled (2s + 6p = 8 electrons)

Importance of Ionic Bonds

• Involved in cell signaling and muscle contraction
• Important in determining cell shapes, catalytic reactions, and neuron functions
• Play a role in shaping tertiary and quaternary proteins
• Help determine the shapes of chromosomes depending on what atoms bond to each other

Importance of Covalent Bonds

• Carbon-Carbon bonds (C-C) form the basis of most biomolecules
• Covalent bonds link together amino acids in chains, creating peptides
• Found holding together amines
• Covalent bonds in large networks give rise to substances with very high melting points (e.g., diamonds)

Types of Bonds

• Ionic bonds: transfer of electrons between a metal and nonmetal
• Covalent bonds: sharing of electrons between two nonmetals
• Metallic bonds: pooling of electrons in a metal lattice