Transcript Ionic Bonding - petersonORHS

Ionic Bonding
Ionic Bonding
• There are three types of chemical bonds,
ionic, covalent, and metallic.
• The first type of bond we will study is the
IONIC BOND.
• An ionic bond is an electrostatic attraction
between a positive particle, also known as
a CATION, and a negative particle, also
known as an ANION.
Electron Dot Notation
Before we can understand the formation of
an ionic bond, we need to know two
things:
– The Octet Rule, one of the most important
rules in chemistry.
– How to write the Electron Dot Notation for
each element on the Periodic Table.
Electron Dot Notation
X represents the element symbol
The dots represent valence electrons
The pattern for drawing electrons helps
us to understand how atoms lose or
gain electrons.
1 2
3
5
6
8
4 7
The maximum number of valence
electrons is 8 .
The Octet Rule
• The Octet Rule: Atoms will either lose,
gain, or share valence electrons in order to
obtain a full set of eight (8) valence
electrons.
• Valence- refers to the outer electrons in an
atom. These are the electrons on the
outer shell, which is the highest energy
level.
Electron Dot Notation
• For the Representative Groups, which are also
called the A Groups, the Group Number is equal to
the number of valence electrons.
(The ones digit of group numbers 1 , 2 , through 18.)
• Take out your Periodic Table and draw the electron
dot notation for the first two elements in each
group. The other elements in that group will be the
same.
>Use these example to help you draw dot notations.
Li Be
B
C
N
O
F
Ne
Labeling the Periodic Table
One exception: Helium only has
two electrons, and we show
them as a pair.
Atoms which have a full set of
valence electrons are very
stable, as stable as Nobel
Gases. (stable = not reactive)
Skip the Transition Metals
-
Formation of an Ionic Bond
Ionic Bonds always involve
the transfer of electrons
from a metal to a
nonmetal.
They do this so that each
may obey the Octet Rule.
Sodium Chloride (table salt)
• The most famous “salt” of all!
• Actually, any ionic compound is
a salt!
• The outer electron of the
sodium transfers to the
chloride
• Then, the oppositely charged
particles stick together by static
electricity.
Another example
Metals form Cations
Metals almost always lose their outer electrons,
forming positive cations:
Na  Na+1 + 1 electron
Ca  Ca+2 + 2 electrons
Al  Al+3 + 3 electrons
Each time, the metals lose their outermost valence
electrons, and the energy level below is full.
Nonmetals form Anions
Nonmetals almost always gain electrons, and
become negative anions.
Cl + 1e-  Cl-1
Chlorine now has 18 e, just
like Argon!
O + 2e-  O-2
N + 3e-  N-3
Each time, the nonmetals gains the number of
electrons needed to obtain 8 valence electrons.
Oxidation Numbers
• An oxidation number
is the charge an atom
would have if it
became an ion.
• Take out your Periodic
Table and label the A
Groups as follows.
AND
Silver = +1
Zinc = +2
Cadmium = +2
Nomenclature
• Nomenclature is a system for naming
chemical compounds.
• It has very specific rules you must follow.
• We will start with the simplest type of ionic
compound, a binary ionic compound.
• Binary- means just two elements are present.
• Ionic Bond--means a metal with a nonmetal
Naming Binary Ionic Compounds
1. Name the metal first
2. Then name the nonmetal,
with an “ide” ending.
• Examples:
NaCl
LiBr
CaF2
Sodium chloride
Lithium bromide
Calcium fluoride
Formula Writing for Binary Ionic Compounds
• Sometimes you will be given the name of
a compound and be asked to write the
chemical formula.
• This requires three careful steps, and a
periodic table.
• Do not guess. Follow the steps!
• “Almost right” is wrong!
Formula Writing Example: Aluminum Oxide
STEP 1: write the symbols, metal first,
then nonmetal.
Al O
STEP 2: above each symbol, write the
oxidation number
Al+3 O-2
STEP 3: Add subscripts so that the
overall charge of the compound is
zero. (“criss-cross” + 6 and - 6 = 0)
+3 x 2 = +6
-2 x 3 = -6
Step 4: (Erase the oxidation numbers,
they are NOT part of the formula,
they just help us get the correct
subscripts!) Al2O3
subscripts
Transition Metals – Groups 3 – 12
The B Groups
• Many transition metals have more than one
possible oxidation state. (Sometimes they give
away one electron, sometimes two, etc. up to
losing 7 electrons! )
• Silver is always +1, Zinc is always +2, and
Cadmium is +2
• Some other metals like Lead and Tin, also
require a Roman Numeral in naming compounds
Which elements need a roman numeral?
It’s faster to say which ones don’t!
(There are a few others, but we won’t ask about them—okay?)
Mark these on your periodic table.
Roman Numerals
Examples:
Name
Copper (I)
Iron (II)
Chromium (III)
Tin (IV)
Formula
Cu+1
Fe+2
Cr+3
Sn+4
It is helpful to label your periodic table with the
oxidation states of the common ones.
Naming Transition Metal Compounds
(except zinc, cadmium—always +2,
and silver always +1…)
If you notice that the formula of a compound has a
transition metal, (except Zn, Cd, Ag) you must use
a Roman numeral in the compound name.
Examples:
FeCl2
CuO
Cr3N2
Is Iron (II) chloride
Is Copper (II) oxide
Is Chromium (II) nitride
Notice that the Roman numeral corresponds to the
subscript of the OTHER ATOM.
Writing Transition Metal Formulas
(except zinc, cadmium—always +2,
and silver always +1…)
Copper (II) fluoride
Step 1 Write element symbols
CuF
Step 2 Put oxidation numbers above each element (The
Roman numeral “(II)” gives the oxidation number for
copper as +2).
Cu+2 F-1
Step 3 Add subscripts to make the charge total = zero,
i.e. “criss-cross”. Note: Use parentheses if you need more
than one of a polyatomic ion on other formulas.
CuF2
Copper II phosphate Cu+2 PO4-3 --- > Cu3(PO4)2
Practice Together
Write formulas for the following:
Tin (II) chloride
Copper (I) oxide
Lead (IV) sulfide
Name the following compounds:
PbCl2
CuO
SnCl4
Polyatomic Ions
• Many common chemical formulas contain
polyatomic ions, which are groups of atoms
bonded together, that carry a charge.
• See your list of polyatomic ions ON your
class periodic table.
• Polyatomic ions stay together as a group as
they undergo reactions.
Common Polyatomic Ions
Hydroxide
Nitrate
Sulfate
Chlorate
Ammonium
OH-1
NO3-1
SO4-2
ClO3-1
NH4+1
Most polyatomic ions are negative, meaning
they have extra electrons.
Ammonium is the only polyatomic ion we use that
is positive. It has given away an electron.
Compounds with Polyatomic Ions
These compounds will have at least three
elements, a metal, and then a polyatomic
ion.
Name the metal first, and then the
polyatomic ion. Don’t change the name of
the polyatomic ion!
Naming Ternary Compounds
(3 or more elements)
NaNO3
CaSO4
Ba(OH)2
NH4Cl
KClO3
sodium nitrate
calcium sulfate
barium hydroxide
ammonium chloride
potassium chlorate
When you see three or more elements, look for a
hidden polyatomic ion !
Never say “calcium sulfur oxide.”
Writing Formulas for Compounds
Containing Polyatomic Ions
Get out a periodic table and a formula chart with the
polyatomic ions on it.
Use the three step process.
Example: Calcium chlorate
Step 1 Write the symbols (polyatomic ion formula
representing the name given) CaClO3
Step 2 Label charges Ca+2 ClO3-1
Step 3 Write subscripts that balance the charges
Ca(ClO3)2
Step 4: Erase charges from your formula
Properties of Ionic Compounds
• Many ionic compounds dissolve in water
• Solutions of ionic compounds conduct
electricity. Ions can move!
• These solutions are called “Electrolytes”
• Ionic compounds have very high melting points
• When melted “molten” they conduct electricity.
Ions can move! (melted salts are conductors)
• Exist as crystals in a “crystal lattice.”
Acids
• The acids that we will study in this unit are
easy to recognize, they contain one or more
hydrogen atoms at the beginning of their
formulas.
• An acid is a compound that dissociates (splits
up) in water to produce hydrogen ions.
– Example:
Hydrochloric acid ---breaks apart in water to form -- >
hydrogen ions and chloride ions.
HCl 
+1
H
+
-1
Cl
Binary Acid Nomenclature
• Binary means two elements.
• These will have hydrogen and one other element.
1. Use the prefix Hydro2. Put an –ic ending on the second element
3. Add the word “acid”
HCl
Hydrochloric acid
HBr
Hydrobromic acid
HF
Hydrofluoric acid
Naming Oxyacids
• These acids will contain hydrogen and a polyatomic ion
which has one or more oxygens
• If the ion ends in –ate change it to an –ic ending
HNO3 

Nitric acid
(Contains the nitrate ion)
H2SO4 

(Contains the sulfate ion)
“Yuck! I ATE something ICKY!”
Sulfuric Acid
Naming Oxyacids
• If the polyatomic ion ends in –ite,
change it to –ous.
• Add the word “acid”
• Ex:
HNO2 
Nitrite ion
H2SO3 
Sulfite ion


Nitrous acid
Sulfurous acid
Bites are delicious