Page 77 Strength of Chemical Bonds Tuesday – Polyatomic Quiz -1’s Wednesday – Polyatomic Quiz Mixed *** Thursday – Polyatomic Quiz Mixed 2 Friday – Polyatomic Quiz Mixed 3

Ionic bonds are in general very strong. The actual strength of the bond is measured by the amount of lattice energy - energy required to separate the cations and anions in the crystal lattice and turn them into single, gaseous atoms. The higher the lattice energy, the stronger the ionic bond was.

The electrostatic forces holding ionic compounds together are typically very strong. This accounts for: High melting points (temperatures) High boiling points Poor conductors as a solid (electrons cannot move much) Good conductors as liquids or when dissolved - called electrolytes (frees electrons to move) Hard and Brittle

Ionic Bonding: A polyatomic ion (radical) is a charged group of covalently bonded atoms. The charge of a polyatomic ion results from an overall excess of electrons (negative charge) or a shortage of electrons (positive charge). Polyatomic ions will form ionic bonds with other charged elements or other polyatomic ions to form a neutral compound.

Covalent bonds are in general not very strong. The actual strength of the bond is measured by bond energy - energy required to separate the bonded atoms into separate atoms. The higher the bond energy, the stronger the covalent bond was.

The forces holding covalent molecules together are typically not very strong. This accounts for: Lower melting points (temperatures) Lower boiling points Poor conductors as a solid, liquids, and when dissolved (electrons cannot move much) Not as hard as ionic compounds and Brittle

Bond length is the average distance between two bonded atoms. The longer the bond, the easier it is to break, to the lower the bond energy.

Covalent Bonding: There are forces that act between molecules to hold them together (not referring to the ones inside the molecules). These forces are called Intermolecular forces (as opposed to Intramolecular forces).

There are three types of intermolecular forces: 1.Hydrogen bonding - the attraction of a hydrogen on one polar molecule to the lone pair of a highly electronegative atom (N, O, F) of a second polar molecule. Click here for a demo of hydrogen bonding in water.

2.Dipole-dipole - a dipole is created by equal but opposite charges that are separated by the short distance of a bond. The positive end of one dipole molecule will be attracted to the negative end of a second dipole molecule, and vise versa.

3.London dispersion forces - resulting from the constant motion of electrons and the creation of instantaneous dipoles. More electrons = stronger London dispersion forces.

Metallic bonds vary greatly in strength. The actual strength of the bond is measured by heat of vaporization - energy required to separate the bonded atoms into separate gaseous (vaporous) atoms. The higher the heat of vaporization, the stronger the metallic bond was.

The forces holding metals together can vary greatly depending on the nuclei in the sea of electrons. This accounts for: Low to high melting points (temperatures) Low to high boiling points Good conductors as a solid (electrons very easy to move) Soft to hard and Malleable and Ductile Low to high tensile strengths Lustrous (electrons very easy to move)

Metallic Bonding: Alloys are mixtures of metals or metals with nonmetals to give the resulting mixture new properties.

Intramolecular Forces Covalent Network (Diamond and Quartz, only) Ionic Molecular (Covalent) Metallic Intermolecular Forces Hydrogen bonding – polar with hydrogen Dipole-dipole – polar only London – nonpolar Review

Page 78 – Bonding Questions