Chapters 8 and 9

Ionic and Covalent Bonding

A chemical bond is a force that holds two atoms together. Chemical bonds may form by the attraction between a positive nucleus and negative electrons OR the attraction between a positive ion and a negative ion.

Important fact… REMEMBER!! All atoms want to have

eight valence electrons, so some atoms lose or gain electrons to achieve that goal and LOOK like a noble gas. When this happens, it is important to remember that the atom has not changed into a noble gas, its nucleus, which gives it its characteristics, remains unchanged. You can dress up like Madonna, but you are still you. You just look different on the outside.

POSITIVE IONS Positive ions form when an atom

loses one or more valence electrons in order to attain a noble gas configuration.

A positive ion is called a cation.

Negative Ions When an atom gains electrons, it

becomes a negative ion.

A negative ion is also called an anion.

Formation of ions Octet Rule – in forming compounds

atoms will try to obtain a noble gas electron configuration.

To do this metals ________ electrons and nonmetals _________ electrons

Metal Examples

Na atom = 1s22s22p63s1 Na

Na1+ = 1s22s22p6 Na1+

Note the 3rd energy level electron was lost to have the same electron configuration as neon

Ne = 1s22s22p6

YOU TRY

Ca = 1s22s22p63s23p64s2 :Ca

Ca2+ =1s22s22p63s23p6 Ca2+

What noble gas does Ca2+ resemble?

The oxidation number on the metal ion (cation) is the positive value of how many electrons were lost.

Ionic Bonds Ionic bonds occur because of the

attraction between oppositely charged ions. Hundreds of compounds contain ionic bonds.

Many ionic compounds are binary, they contain only 2 different elements. Binary ionic compounds usually contain a metallic cation and a nonmetallic anion.

Example Calcium fluoride CaF2

Calcium, a group 2A metal with the electron configuration [Ar]3s2, has 2 valence electrons. Fluorine, a group 7A nonmetal with the electron configuration [He]2s22p5, must gain one e- to attain the noble gas configuration of neon. Because the number of e- lost must equal the number of e- gained, it will take two fluorine atoms to gain the two e- lost from one calcium atom. The compound formed will contain one calcium ion with a charge of 2+ for every two fluoride ions, each with a charge of 1-.

Ca+2 + F-1 CaF2

Oxidation numbers must equal zero, when added together.

Ca+2 + F-1+F-1

Properties of Ionic Compounds Attraction and repulsion between positive and

negative ions cause the ions to be packed into a specifically shaped particle called a crystal lattice. In a crystal lattice each positive ion is surrounded by negative ions and each negative ion is surrounded by positive ions.

Melting and Boiling Points Because ionic bonds are relatively

strong, the crystals that result require a large amount of energy to be broken apart. Therefore, ionic compounds have high melting and boiling points.

Conductor of electricity? In the solid state, ionic compounds are

nonconductors of electricity because of the fixed positions of the ions. However in a liquid state or when dissolved in water, ionic compounds are electrical conductors because the ions are free to move. An ionic compound whose aqueous solution conducts and electric current is an electrolyte.

Lattice Energy The energy required to separate one

mole of the ions of an ionic compound is referred to as lattice energy. The more negative the lattice energy, the stronger the force of attraction. Smaller ions have a more negative value for lattice energy because the nucleus is closer to and thus has more attraction for the valence e-.

Formulas for Ionic Compounds The simplest ratio of the ions

represented in an ionic compound is called a formula unit. A monatomic ion is a one-atom unit (Mg2+ or S2-). The charge of a monatomic ion is its oxidation number. Most transition metals and group 3A and 4A metals have more than one oxidation numbers.

The oxidation number of an element in an ionic compound equals the number of electrons transferred from an atom of the element to form the ion.If you add the oxidation number of each ion multiplied by the number of these ions in a formula unit, the total must be zero.

Let’s practice Potassium plus sulfur yields _______ Sodium plus oxygen yields _______ Aluminum plus fluoride yields

______ Cesium plus nitrogen yields _______ Magnesium plus chlorine yields

______

Polyatomic Ions An ion that is made up of more than

one atom is called a polyatomic ion. The charge given to a polyatomic ion applies to the entire group of atoms. The polyatomic ion acts as an individual ion. Because a polyatomic ion exists as a unit, never change subscripts of the atoms within the ion.

Oxyanion An oxyanion is a polyatomic ion

composed of an element, usually a nonmetal, bonded to one or more oxygen atoms.

Go to Nomenclature rules p. 3

Metallic Bonds & Properties Metals do not bond ionically, but

they form lattices similar to ionic crystal lattices. The electron sea model proposes that all the metal atoms in a metallic solid contribute their valence electrons to form a “sea” of electrons.

Delocalized electrons The electrons present in the outer

energy levels of the bonding metallic atoms are not held by any specific atom and can move easily from one atom to the next. Because they are free to move, they are often referred to as delocalized electrons. A metallic bond is the attraction of a metallic cation for delocalized electrons.

Electron sea model

Properties of Metals

1) Moderately high melting points and high boiling points.

2) Malleable and ductile3) Durable4) Good conductors of heat and

electricity, because the electrons are free to move and can move heat easily

Alloys An alloy is a mixture of elements

that has metallic properties. Examples of common metal alloys1. Brass - Cu 67-90%, Zn 10-33%2. Bronze - Cu 70-95%, Zn 1-25%, Sn 1-

18%3. 10 carat gold – Au 42%, Ag 12-20%,

Cu 38-46%4. Sterling silver – Ag 92.5%, Cu 7.5%