Notes 12.1

Characteristics of Chemical BondsNotes 12.1Types of Chemical BondsA bond is a force that holds groups of two or more atoms together and makes them function as a unitThe strength of a bond can be measured by the energy required to break the bond - bond energyIonic substances are formed when an atom that loses electrons relatively easily reacts with an atom that has a high affinity for electrons. An ionic compound forms when a metal reacts with a nonmetal.

Types of Chemical BondsCovalent bonding is when electrons are shared.In covalent bonding two identical atoms share electrons equally. The bonding results from the mutual attraction of the two nuclei for the shared electrons.The unequal sharing of electrons results in a polar covalent bond.

ElectronegativityWhen different nonmetals react, a bond forms in which electrons are shared unequally, giving a polar covalent bond. The unequal sharing of electrons between two atoms is described by a property called electronegativity: the relative ability of an atom in a molecule to attract shared electrons to itself.

ElectronegativityThe polarity of a bond depends on the difference between the electronegativity values of the atoms forming the bond.Chart on page 403 Differences: 0 to .3 = covalent bond (non polar) .4 to 1.9 = polar covalent bonds 2.0 > = ionic bonds

Dipole Moment

Bond Polarity

The fact that the water molecule is polar has a profound effect on its properties. They can surround and attract both positive and negative ions. These attractions allow ionic materials to dissolve in water. The polarity of water causes water molecules to attract each other strongly.Much energy is required to change water from a liquid to a gas. It is the polarity of the water molecule that causes water to remain a liquid at the temperatures on the earths surface.