Ionic Bonding
Students know atoms combine to form molecules by sharing electrons to form covalent or metallic bonds or by exchanging electrons to form ionic bonds.
Students know salt crystals, such as NaCl, are repeating patterns of positive and negative ions held together by electrostatic attraction.
Bonds Forces that hold groups of
atoms together and make them
function as a unit.
Ionic bonds – transfer of electrons
Covalent bonds – sharing of electrons
The Octet Rule – Ionic Compounds
Ionic compounds form so that each atom, by gaining or losing electrons, has an octet of electrons in its highest occupied energy level.
Metals lose electrons to form positively-charged cations
Nonmetals gains electrons to form negatively-charged anions
Ionic Bonding:The Formation of Sodium
Chloride
Sodium has 1 valence electron
Cl: 1s22s22p63s23p5
Na: 1s22s22p63s1
Chlorine has 7 valence electrons
An electron transferred gives each an octet
Ionic Bonding:The Formation of Sodium
Chloride
Cl- 1s22s22p63s23p6
Na+ 1s22s22p6
This transfer forms ions, each with an octet:
Ionic Bonding:The Formation of Sodium
Chloride
Cl- Na+
The resulting ions come together due to electrostatic attraction (opposites attract):
The net charge on the compound must equal zero
Ionic Bonds
Metal to NonmetalHigh END
Metal forms cationNonmetal forms anion
Sodium Chloride Crystal Lattice
Ionic compounds form solid crystals at ordinary temperatures.Ionic compounds organize in a characteristic crystal lattice of alternating positive and negative ions.All salts are ionic compounds and form
crystals.
Ionic solids are brittle
+ - + -+- +-
+ - + -+- +-
Force + - + -
Strong repulsion breaks crystal apart.
Visual Concept
Characteristics of Ion Bonding in a Crystal Lattice
Properties of Ionic Compounds
Structure: Crystalline solids
Melting point:
Generally high
Boiling Point:
Generally high
Electrical Conductivity:
Excellent conductors, molten and aqueous
Solubility in water:
Generally soluble
Lattice Energy- the ionic bond
---the energy released when the crystal lattice formation is formed
---Lattice energies are listed as negative values to indicate that energy is given off when ions come together to form the ionic crystal.
The greater the lattice energy… the stronger the ionic bonding!
Vocabulary
COMPOUND
ternarycompound
binarycompound
2 elementsmore than 2
elements
NaNO3NaCl
Vocabulary
ION
polyatomicIon
monatomicIon
1 atom 2 or more atoms
NO3-Na+
e-
3p+
lithium atomLi
e-
loss of one valence
electron
e-
e-
lithium ionLi+
3p+e-
e-
9p+
fluorine atomF
e-
e-
e-
e-
e-
e-
e- e-
e-
gain of one valence
electron
fluoride ionF1-
9p+e-
e-
e-
e-e-
e-
e-
e-
e-
e-
e-
Formation of Cation
3p+
lithium atomLi
e-
loss of one valence
electron
e-
e-
lithium ionLi+
3p+e-
e-
e-
Formation of Anion
9p+
fluorine atomF
e-
e-
e-
e-
e-
e-
e- e-
e-
e-
gain of one valence
electron
fluoride ionF1-
9p+e-
e-
e-
e-e-
e-
e-
e-
e-
e-
Formation of Ionic Bond
fluoride ionF1-
9p+e-
e-
e-
e-e-
e-
e-
e-
e-
e-
lithium ionLi+
3p+e-
e-
Ionic bonding: Li + Cl1e-
3p+
4n02e- 17p+
18n08e-8e-2e 3p+
4n02e-1e- 17p
+18n07e- 8e- 2e-
Li Cl [ Cl ]–
[Li]+
lithium atom chlorine atom lithium ion chloride ion
Ionic bonding: Li + C
Li + Cl [ Cl ]–[Li]+
Ionic compound formation equation
Ionic bonding: Mg + O
12p+
12n02e- 8e- 2e-
1e-
[ O ]2–
[Mg]2+
6e- 2e-
8n0 8p+
1e-
8e- 2e-
8n0 8p+ 12p+
12n02e- 8e-
OMg
Lewis Dot Diagrams and
BONDING (Ionic )
How do we show the valence electrons for different elements?
* dot diagrams were developed by American, G.N. Lewis, in the 1920's* they are called Lewis structure or Lewis dot diagrams
Electron-Dot Notation
To keep track of valence electrons, it is helpful to use electron-dot notation.
Electron-dot notation shows only the valence electrons of an atom of a particular element, indicated by dots placed around the element’s symbol. The inner-shell electrons are not shown.
Click below to watch the Visual Concept.
Visual Concept
Electron-Dot Notation
Hydrogen has one valence electron
Nitrogen has five valence electrons.
Mg
Write the electron dot diagram for
• Na• Mg• C• O• F• Ne• He
1s22s22p63s1
1s22s22p63s2
1s22s22p2
1s22s22p4
1s22s22p5
1s22s22p6
1s2
Na
C
O
F
He
Ne
Ionic Bonding
Na Cl
transfer of electron
+1 -1
NaCl
Ca +2
P -3Ca
+2
P
• All the electrons must be accounted for!
+2
Ionic Bonding
Ca -3
Ionic Bonding
Ca3P2Formula Unit
Ca2+
Ca2+
Ca2+
P3-
P 3-
Ca2+
P3- Ca2+
P3-
Ca2+
Ionic Formation Equation
Ca
P + 2[ P ]–33[Ca]
+2
* monatomic ions can be written with dot diagrams
* as before, dots are used to demonstrate e-
* symbol is in [brackets] to represent ions
* charge is placed on the upper right corner
Do the dot diagrams for Na, Mg, Al, P, S, Cl ions
+1
-1
PracticeDraw the Lewis Dot Diagrams
for the following compounds:1. Lithium iodide2. Calcium chloride3. Potassium oxideExample: Magnesium Chloride
[Mg]+22[ Cl ]-1
Polyatomic Ions
An example of a polyatomic ion is the ammonium ion: . It is sometimes written as to
show that the group of atoms as a whole has a charge of +1.
The charge of the ammonium ion is determined as follows:
seven protons in the nitrogen atom plus the four protons in the four hydrogen atoms give the ammonium ion a total positive charge of
+11.
When nitrogen and hydrogen atoms combine to form an ammonium ion, one of their electrons is lost, giving the polyatomic ion a total negative charge of -10.
The total charge is therefore (+11) + (-10) = +1.
Some examples of Lewis structures of polyatomic ions are shown below.