Ionic Bonding How Elements Form Compounds I CAN

Ionic Bonding How Elements Form Compounds

• I CAN describe chemical bonding and determine an ionic chemical formula.

Chemical Bonding • Chemical Bonding is the joining of two or more atoms to form a compound. • Bonding occurs when atoms transfer electrons between them, or, in some cases, move close together and share electrons between them.

Valence Electrons • During bonding, the only electrons involved are those at the outer edge of the atom’s electron cloud. • These are called VALENCE ELECTRONS. • Atoms can have between 1 and 8 Valence Electrons.

ATOMS BECOME IONS • When an atom gains or loses electrons by transfer there is a change in its overall charge, the atom is transformed into another form called an ION

• POSITIVE IONS are called CATIONS and are formed from METALS on the LEFT SIDE of the periodic table. • NEGATIVE IONS are called ANIONS and are formed from NON-METALS on the RIGHT SIDE of the periodic table. • We will only look at the SIX MAIN GROUPS for right now.

IONIC BONDING • IONIC BONDING occurs between two IONS with OPPOSITE CHARGES. • Remember OPPOSITES ATTRACT!

Characteristics of IONIC Compounds • Generally consist of a METAL CATION and a NON-METAL ANION. • High melting points • Almost always solid at room temperature • Brittle • Generally not very flammable • Dissolve in water [electrolytes]

Forming an IONIC Compound • The simplest IONIC COMPOUNDS are called BINARY IONIC compounds. • They consist of only TWO DIFFERENT kinds of atoms…. . one a POSITIVE ION from the metal side of the PT and the other a NEGATIVE ION from the non-metal side of the PT. • Together their CHARGES add up to equal ZERO.

TO DETERMINE AN IONIC FORMULA FOLLOW THESE STEPS 1. Find the elements in the Periodic Table and write down their symbols. 2. Use the element’s location on the Periodic Table to find the charge of its ION…go to the TOP of the column and get the charge. 3. If they have EQUAL BUT OPPOSITE CHARGES (for example a +2 and a -2), then the formula is simply ONE ATOM OF EACH since they add up to equal 1. ZERO. 2. 4. If the charges are not equal but opposite (such as 3. +3 and -2) CRISS-CROSS the charges (NO SIGNS 3. numbers only). • Write the FORMULA. A formula contains CHEMICAL SYMBOLS that tell what elements are in the compound and SMALL NUMBERS called 1. SUBSCRIPTS which tell how many of each kind of atom are in the 2. compound.

EXAMPLE PROBLEM • What would be the formula of a compound of Potassium and Bromine? • 1. Find both elements on the PT, get their SYMBOL and CHARGE: ( +1 ) K ( -1 ) = 0 Br

2. If they are EQUAL BUT OPPOSITE then they cancel each other out, so the formula is ONE ATOM of each element. • Positive element always goes first! (+1 ) + ( -1 ) = 0 K Br Formula is KBr

• PROBLEM • What is the formula for an ionic compound of Magnesium and Chlorine?

• Determine the symbol and charge of both elements see if they are equal. If not, CRISS-CROSS the numbers! • (+2 ) + (-1 ) = 0 • Mg Cl • Mg 1 Cl 2 = Mg. Cl 2 • Remember ONE is not usually written as a subscript!

Problem What is the formula of an ionic compound of Aluminum and Oxygen? • (+3) + ( -2 ) • Al O

• (+3) + (-2 ) = 0 • Al O • So the formula is: Al 2 O 3

Practice Problems • Find the formula for a compound made with each pair of atoms: • 1. Sodium and Sulfur • 2. Calcium and Chlorine • 3. Potassium and Phosphorus • 4. Aluminum and Nitrogen • 5. Magnesium and Fluorine