Download Chemical Bonding - Magoffin County Schools

The Periodic Table,
Valence Electrons
and 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 [Ve-].
• When atoms come into close contact with
each other, VALENCE ELECTRONS can
be TRANSFERRED from one atom to
another.
• Typically, atoms on the LEFT SIDE of the
periodic table [the METALS] LOSE
electrons.
• Atoms on the RIGHT SIDE of the periodic
table [the NON-METALS] gain electrons.
• The number of electrons GAINED or LOST
depends on the GROUP NUMBER the atom
is in:
• LOSE ELECTRONS GAIN ELECTRONS
• Group 1 loses 1e• Group 2 loses 2 e• Groups 13 loses 3 e-
Group 15 gains 3 eGroup 16 gains 2 eGroups 17 gains 1 e-
Atoms become IONS
• When an atom gains or loses electrons
and 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.
• NEGATIVE IONS are called ANIONS and
are formed from NON-METALS.
Charges of IONS
• Family 1 ions = +1
• Family 2 ions = +2
• Family 13 ions = +3
Losing electrons is
called OXIDATION
and make + charged
ions.
[Family 14 bonds in a different way – more later]
• Family 15 ions = -3
• Family 16 ions = -2
• Family 17 ions = -1
Gaining electrons is
called REDUCTION
and make - charged
ions.
• [Family 18 doesn’t form chemical bonds.]
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
• What would be the formula for a compound resulting
from ionic bonding between Potassium and Bromine?
• 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
predict the charge of its ION.
• 3. Criss-cross the charges (NO SIGNS) and multiply.
• 4. Write the FORMULA.
• Write the symbols and charges in a
BRACKET above the symbols in this
manner:
[ +1 ] + [ -1 ] = 0
K
Br
• BALANCE the charge by criss-crossing
the numbers [don’t worry about charge]
and multiplying each bracket.
1 [ +1 ] + 1 [ -1 ] = 0
K
Br
• To write the FORMULA,
• Write the symbol of the POSITIVE ION first, the
NEGATIVE ION second.
– Place the number you MULTIPLIED the bracket by
AFTER and slightly BELOW the symbol.
– This number is called a SUBSCRIPT.
1[ +1 ] + 1[ -1 ] = 0
K
Br
K1
Br1
• If the number is ONE, it is understood and
you DO NOT have to write it.
– Think of X in math….1X = X
• So the formula for a compound of
Potassium and Bromine is:
•
KBr
• PROBLEM
• What is the formula for an ionic compound
of Magnesium and Chlorine?
• Determine the symbol and charge of both
elements and cross the numbers:
• 1 [+2 ] + 2 [-1 ] = 0
• Mg
Cl
• Mg1Cl2 = MgCl2
• 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] +
•
Al
[ -2 ]
O
• +6
-6
•2 [ +3] + 3 [ -2 ] = 0
•
Al
O
• So the formula becomes:
• Al2O3