Chapter 8

Ionic Compounds

8.1 Forming Chemical Bonds The force that holds two atoms together

is called a Chemical Bond. Chemical Bonds (ionic, covalent, metallic) :– May form due to the attraction

between “+” charged nucleus and “–” charged electrons, or

– May form due to the attraction between a Positive ion and a negative ion.

Cation - A positively charged ion. Formed when an atom loses an electron, thereby gaining a net positive charge. (K+)

Anion – A negatively charge ion. Formed when an atom gains and electron, thereby gaining a net negative charge. (F-)

Look for the oxidation number on the periodic table to indicate the type of ion formed.(+2,-2, etc.)

Ions that are formed from a single atom are called monatomic ions. They will be shown by only one chemical symbol of the element and either a (+) or (-) sign above it. (Mg+2 or F-

)

If ions are formed from groups of atoms they are called polyatomic ions. These will have several element symbols listed.(OH- or SO42-)

Valence Electrons are responsible for the chemical properties of atoms.

– Located in the outer energy level

– Involved in the formation of chemical bonds between two atoms.

– Total number of valence electrons = group number. (Na has 1, (Group 1 element)

Valence Electrons are shown using a diagram called, the Electron Dot structure.

– “Dots” are valence electrons (total number 1-8 and equal to the group number).

– Element’s Symbol is in the middle.

Write the symbol of the element “X”.

Put one dot for each valence electron

Don’t pair up until they have to

X

Example: The Electron Dot diagram for Nitrogen

Nitrogen has 5 valence electrons. (group 5)

First we write the symbol.

NThen add 1 electron at a time to each side.Until they are forced to pair up.

Learning Check

A. X would be the electron dot formula for

1) Na 2) K 3) Al

B. X would be the electron dot

formula

1) B 2) N 3) P

Elements in the same group have similar chemical properties.

Electron Affinity – Attraction an atom has for electrons. High=Reactive

Ionization Energy- How easily an atom loses an electron. Low=Reactive– High IE and low EA = lack of

chemical reactivity.– Low IE and high EA = Chemically

reactive.

Stable Electron Configurations All atoms react so as to achieve a

noble gas configuration of 8 valence electrons.

ls called the octet rule.

Ar

8.2 IONIC BONDS Ionic Bond-The electrostatic force that holds

oppositely charged particles (anions and cations) together in an ionic compound.

Ionic compounds result when metals react with nonmetals. Ionic compounds are called salts.

Simplest ratio is called the formula unit (Ca3P2).

The ionic bond is formed through the transfer of electrons.

Electrons are transferred to achieve noble gas configuration (8).

Ionic Bonds: One Big Greedy Thief Dog!

Properties of Ionic Compounds Crystalline lattice structure.

– A 3-dimensional geometric arrangement of particles. Regular repeating arrangement of ions in the solid.

Ions are strongly bonded. Structure is hard and rigid. High melting points and boiling points-

because of strong forces between ions.

An ionic compound is an electrolyte if it conducts electricity when it is liquid or in aqueous solution.

Lattice energy- The strength of the force holding the ions together in an ionic compound. The more negative the number, the stronger the force.

Lattice energy must be exceeded in order to

break the ionic bond.

8.3 Names and Formulas for Ionic Compounds

Writing the chemical formula of an ionic compound:****Need the oxidation number from periodic table.

1. Write the symbol of the positive ion first with its charge.( Mg+2), from the PT or common ions table.

2. Write the symbol for the negative ion and its charge next to the positive one. (Mg+2 O-2 ).

3. Rewrite the formula and move the numbers to the opposite corner and drop the signs. (Mg2O2) then reduce to simplest ratio (MgO). (swap and drop then reduce).

4. If there is a polyatomic ion involved use a parenthesis.

– Al+3 SO4-2 becomes

Al2(SO4)3

– Remember: The charge number comes from the oxidation number on the periodic table (single ion), or common ions table for polyatomic ions (2or>).

When naming binary ionic compounds the name of the (+) cation goes first, followed by the name of the (-) anion.

Anions are named by replacing the suffix of the elements name with the suffix “ide” (CsBr is Cesium Bromide).

If there is more than one oxidation number (charge), which ever one is used goes in parenthesis as a roman numeral. (Fe+3O-2

becomes Fe2O3 and is called Iron(III) Oxide.

(Iron can be a +3 or +2)

When naming an ionic compound with a polyatomic ion(s) in it, use the table of common ions.

– (Example: Cu(NO3)2 would be called Copper(II) Nitrate.

Naming Ionic Compounds (continued)

* Polyatomic ions each have specific names which should be memorized so they can be recognized on sight.

(At this point, if you are asked to name any compound that contains more than two elements, it will contain at least one polyatomic ion.)

Formula Name

C2H3O21- acetate

CO32- carbonate

HCO31- bicarbonate

NH41+ ammonium

A few of the more common polyatomic ions

Formula Name

NO31- nitrate

OH1- hydroxide

PO43- phosphate

SO42- sulfate

Naming Ionic Compounds: Examples

Na2SO4 sodium sulfate

Fe(NO3)2 iron (II) nitrate

AlCl3 aluminum chloride

PbI4 lead (IV) iodide

(NH4)3PO4 ammonium phosphate

Mg3N2 magnesium nitride

C2H3O21- acetate

CO32- carbonate

HCO31- bicarbonat

e

NH41+ ammoniu

m

NO31- nitrate

OH1- hydroxide

PO43- phosphate

SO42- sulfate

* Groups I & II, Al, Zn, Cd, and Ag need no Roman numeral.

AgC2H3O2 silver acetate

8.4 Metallic Bonds Metallic bonds are formed when metal (+)

cations attract free valence (-)electrons A sea of electrons moves throughout the

entire metallic crystal, producing this attraction.

Metals hold onto their valence electrons very weakly.

The electrons are called decentralized electrons because they are free to move and not attached to any one atom.

Electron Sea Model

+ + + ++ + + +

+ + + +

Explains the properties of metals. Properties of Metals

– Conduct electricity

– Ductile

– Malleable

Alloys Solutions made by dissolving metal into

other elements- usually metals. Melt them together and cool them. If the atoms of the metals are about the

same size, they substitute for each other

Called a substitutional alloy

Alloys If they are different sizes the small one

will fit into the spaces of the larger one Called and interstitial alloy