Chapter 5 Notes
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Chapter 5
Ions and Ionic Compounds
Unit Essential Question:
What are the characteristics of
ionic compounds?
Lesson Essential Question:
Why do atoms form ions?
Section 1: Simple ions
How reactive atoms are depends upon the
number of valence electrons.
Certain number makes atoms stable.
Octet rule – elements with full outer energy
levels tend to be stable. Full energy levels
have eight electrons.
All noble gases have a satisfied octet rule
except He (2 valence electrons).
Don’t want to gain or lose an electron.
Stability
This will be an important theme in this chapter
and in the next.
Being stable is the goal of atoms and is the
reason why bonding takes place.
By bonding, atoms change their electron
configurations to become more stable.
There are several terms/phrases that you will see
that indicate an atom is stable:
#1: Octet rule is satisfied/achieved.
#2: The atom has a noble gas configuration.
#3: The atom has a full valence/outer shell.
Alkali Metals & Halogens
Most reactive elements.
Alkali metals-1 valence e- ; halogens- 7 valence e Full valence shell is achieved if alkali metals lose one e-
and halogens gain one e-.
Often bond together- the alkali metal gives an e- to the
halogen.
Example:
K: [Ar]4s1 and Cl: [Ne]3s23p5
K will lose one e- and Cl will gain one e-.
Each now has the same configuration: [Ne]3s23p6
Both have the same configuration as the noble gas
argon- they’re now stable, have an octet!
Ions
Ion – atom or molecule that has a charge because it has
gained or lost electrons. Identity does not change!
Cation – ion with a positive charge; e- are lost.
The ‘t’ in cation resembles a + sign. This can help you remember
that cations are positive.
Anion – ion with a negative charge; e- are gained.
Ions form as atoms change their valence e- to try and
achieve a noble gas configuration.
As we saw before:
K = [Ar]4s1 loses 1 e- ; K is now a K+ ion.
Cl = [Ne]3s23p5 gains 1 e- ; Cl is now a Cl- ion.
Patterns of Charges on the Periodic Table
Since elements
in the same group
have the same #
of valence e-,
elements in the
same group often
form the same
ions (in the s and
p blocks).
+1 +2
+3
-3
-2
-1
*Metals tend to lose e- (become cations) and
nonmetals tend to gain e- (become anions).
No patterns in the d-block
Transition metals do not follow a pattern according to
group number.
Almost all transition metals form more than one cation.
Pb4+
Ions- what changes and what doesn’t
Ions and Ionic compounds
Properties change!
Compounds formed from ions have very different
properties from the original atoms.
Ex: sodium and chlorine vs. sodium chloride.
Remember:
Identities don’t change!
Ions do not BECOME noble gases!
Have electron configurations of noble gases and
therefore behave like noble gases.
They become more stable.
Lesson Essential Question:
What properties result from
forming ionic bonds?
Section 2: Ionic Bonding and Salts
Ionic bonds form when oppositely charged ions attract.
Salt – name given to many ionic compounds.
Ex: NaF, KCl, CaSO4, etc.
Thousands of ionic compounds are called salts.
Ionic compounds as a whole are neutral in charge.
Not just one cation and one anion come together- many
are attracted.
Results in a tightly packed crystal lattice
structure.
Energy and Ionic Bonding
There are numerous steps to forming ionic
compounds from elements (ie: forming NaCl from
Na and Cl).
Energy is involved in every step.
Overall, more energy is released than is
absorbed.
This makes forming ionic compounds
spontaneous (favorable).
Lattice energy: energy released when ionic
bonds form.
Properties of Ionic Compounds
Attractive forces (+ and -) make bonds very strong.
High melting and boiling points.
Usually solids at room temperature.
Conduct electricity when melted (molten) or in solution
(dissolved in water).
Most dissolve well in water.
Hard and brittle as crystals.
Due to repeating pattern of ions.
Crystal lattice – regular pattern in which a salt crystal
is arranged.
Made up of many repeating units (smallest called a unit
cell).
Lesson Essential Question:
How are ionic bonds represented
using formulas and names?
Section 3: Names and Formulas
of Ionic Compounds
Naming Monatomic Ions
Monatomic ions – one atom with a charge.
Mono = one.
Ex: Al+3, O-2
Cation names do not change. Add ‘ion’ after the name.
Na+ = sodium ion; Ba+2 = barium ion
Transition metals can form more than one ion. In order
to tell them apart Roman Numerals are used.
Value of Roman
Cu+ = copper(I); Cu+2 = copper(II)
Numeral tells
+2
+4
Sn = tin(II); Sn = tin(IV)
you the size of
the charge.
Anion names do change.
“-ide” ending is added at the end of the element name.
S-2 = sulfide; N-3 = nitride; F- = fluoride
Naming Polyatomic Ions
Polyatomic ions – 2 or more atoms with a charge.
Poly = many.
Ex: NH4+, SO4-2 (ammonium, sulfate)
These are names that you must memorize.
Ion Chart
You should know all cations and all starred* anions on the
ion chart.
Remember- monatomic ions in the s and p blocks can be
determined just by looking at the periodic table! These are
not included on the ion chart but you are expected to know
them!
There will be a quiz on ion names and charges!
Naming Ionic Compounds
ALWAYS name and write the cation before the anion.
Binary – compounds with 2 elements.
Use rules for naming monatomic ions.
Ex: NaCl: sodium chloride (Na+ and Cl-)
CaBr2 calcium bromide (Ca+2 and Br-)
Recall use of Roman numerals for transition metal
cations with multiple possible charges!
Ex: FeCl3: iron (III) chloride (Fe+3 and Cl-)
Cu2O: copper (I) oxide (Cu+ and O-2)
To help you figure out the charge:
For right now looking at the subscript for the anion will
help you determine the charge on the transition metal
cation.
Naming ionic compounds cont.
Naming compounds with 3 or more elements:
Use rules for naming monatomic ions AND polyatomic ion
names.
Ex: K3PO4: potassium phosphate (K+ and PO4-3)
(NH4)2S : ammonium sulfide (NH4+ and S-2)
Notice that parentheses are placed around polyatomic ions
whenever there are more than one used in the chemical
formula.
o Otherwise looks like: NH42S
Another ex: NH4NO3 : ammonium nitrate (NH4+ and NO3-)
Writing Chemical Formulas for Ionic
Compounds
Compounds must be neutral!
aluminum oxide
Positive charge = negative charge.
Use the “criss-cross” method:
Step 1: determine ions from the name.
Step 1: Al+3
O-2
Step 2: Al+3
Step 2: criss-cross numbers only.
O -2
Step 3: Al2O3
Step 3: be sure to give the lowest ratio possible.
Reduce if necessary! (ex: Sn2O4 SnO2)
Note that the positive ion is written first!
Use parentheses if there is more than one polyatomic ion!
Ex: calcium nitrate: Ca(NO3)2 (NOT: CaNO32)
Don’t write 1’s in formulas.
We assume there’s 1 if there’s no number written after the
charge.