Ionic Bonds
January 5, 2016
8th grade Chapter 4.2
Meme Moment
How to Count Valence
Electrons
• Find the element.
• Focus on that row (period).
• Count s+p spots to get to that element.
Electrons & Stability
• When an atom has a full set (8) or empty set (0) of
valence electrons, it is stable
o H, He, Li, Be are OK with just 2
• If an atom doesn’t have a full set of valence
electrons, it will try to steal, give, or share them with
other atoms
• This makes chemical bonds
o Stealing/giving = ionic bond
o Sharing = covalent bond
• When it’s very close to a full set (alkali metal or
halogen) it will work extra hard and be very
reactive
Ions
• If an atom wants a full or empty valence set, it can
steal or give away electrons
• If # electrons changes, the number of positive protons
& negative electrons won’t match
• This means that the atom will have an overall charge
# protons – # electrons = charge
# electrons normally - # electrons now = charge
• E.g. Sodium gives away 1 electron. 11-10 = +1 charge
• Could also show 1 – 0 = +1 charge
Ions, part 2
# protons – # electrons = charge
# electrons normally - # electrons now = charge
• Use a Lewis diagram or the periodic table to check how
many electrons are needed
• E.g. Sodium gives away 1 electron. 11-10 = +1 or 1-0=+1
• Show whether the charge is + or –
• Draw the charge to the top right side of the symbol
Na+ or Na+1 or Na1+
Practice!
Atom
O
Ca
Br
K
How to get a
full or empty
valence set?
needs 2 more
Math
Symbol
6-8= -2
O-2
Ionic Compounds
• Ions pair up so that the molecule is neutral overall
• Positive charge written first
Na+ with Cl- makes NaCl (+1-1=0)
Mg+2 with O-2 makes MgO (+2-2=0)
• If the charges don’t match, use subscripts to balance
Mg+2 with Br – makes MgBr2 (+2 + 2(-1) = 0)
Na+ with N-3 makes Na3N (3(+1) -3 = 0)
Practice!
Atoms
Ions
Math
Formula
K, O
K+, O-2
2(+1)-2=0
K2O
Ca, Br
B, Cl
Al, O
Polyatomic Ions
Formula
NH4+
NO3HCO3CO3-2
SO4-2
Name
ammonium
nitrate
bicarbonate
carbonate
sulfate
Charge
+1
-1
-1
-2
-2
Polyatomic Ions in
Compounds
• Treat polyatomic ions like an atom of their own
NH4+ with Cl- makes NH4Cl (+1-1=0)
Mg+2 with CO3-2 makes MgCO3 (+2-2=0)
• If the charges don’t match, use subscripts to balance
• Use parentheses around the polyatomic ion
Mg+2 with NO3– makes Mg(NO3)2 (+2 + 2(-1) = 0)
NH4+ with N-3 makes (NH4)3N (3(+1) -3 = 0)
Naming Ionic
Compounds
• First word is the first element (the positively-charged
ion)
• Second word is the second element, changed to
“ide”
• Use polyatomic names instead if you have a
polyatomic ion
• MgO is magnesium oxide
• NH4Cl is ammonium chloride
• KBr is potassium bromide
Practice!
Ions
NH4+, Br Ca+2, NO3Na+, HCO3K+, CO3-2
Al+3, SO4-2
Ionic
Name
Compound
ammonium bromide
NH4Br
Properties of Ionic
Compounds
• Conduct electricity when melted or dissolved in
water
• Hard
o Na can be cut with a spoon. NaCl can’t
• Brittle
• Form crystals
• High melting point
o Na melts at 98°C, but NaCl melts at 801°C
Periodic Table