Ionic bonding and compounds An ionic compound is composed of positive and negative ions that are combined so that the numbers of positive charges and negative charges are equal.

Ionic bonding and compounds Na and Cl combine to form NaCl, sodium chloride Na+ Cl- One positive charge Na+ combines with one negative charge, Cl-

Ionic bonding and compounds CaI2 , Calcium Iodide Ca combines with I Ca2+ I- To balance the pos and neg charges, the compound combines 1 Ca with 2 I Ca2+ I- I- Now the charges balance

Ionic bonding and compounds The simplest form of a molecular compound is a molecule, but ionic compounds ARE NOT molecular compounds so we call the simplest unit of an ionic compound a formula unit

Ionic bonding and compounds A formula unit is the simplest collection of atoms of an ionic compound Ionic compound – formula unit Molecular compound - molecule

Ionic compounds form in what are called crystal lattices A crystal lattice is an orderly arrangement of ions to minimize the ions potential energy

Ionic crystal lattices are hard but brittle, can break easily All it takes to break an ionic compound is to shift the ions, one ion over to break the ionic bonds and the ionic compound breaks apart

The force that holds ions together, the positive and negative attraction, is very strong The forces of attraction between atoms in molecular compounds are weaker than the forces of attraction between ions in an ionic compound.

Bond strength in ionic compounds is measured by the lattice energy Lattice energy – is the energy released when one mole of an ionic crystalline compound is formed from gaseous ions.

Lattice energies kj/mol NaCl -787.5 CaF2 - 2634.7 LiF - 1032 Negative energy values mean the energy is released when the solid crystals are formed

What is the relationship between lattice energies and bond strength? NaCl -787.5 kj/mol CaF2 -2634.7 kj/mol

Polyatomic ions A charged group of covalently bonded atoms is called a polyatomic ion

Ionic compounds solid v aquaeous Solid ionic compounds cannot carry an electrical charge. Ionic compounds dissolved in water will conduct electricity

Metallic bonding

Metallic bonds Consist of the attraction of free-floating valence electrons with the positively charged metal ions. so, it’s a positive and negative attractive force that holds the bonds together

Metal atoms arranged in very compact and orderly patterns

sea of electrons

The arrangement of atoms in a metal allows the metal to bend or change shape without breaking or shattering. (malleable) Ionic crystal bonding is different from metallic bonding.

Metallic vs Ionic Metallic bond ionic bond Atoms can flow atoms are not able to Around each other flow, will shatter if shifted

alloys Alloys are made up of two or more metal elements. Bronze is an alloy of copper and tin. Used early in history to make weapons (bronze age) Stainless steel is also an alloy of Fe 80.6%, Cr 18%, C .4%, Ni 1% Alloys are important, their properties are often superior to those of the individual elements.

Diatomic Molecules There are 7 diatomic molecules, or elements that cannot exist as a single atom, but two atoms of the same element bonded together. N2, O2, H2, F2, Cl2, Br2, I2