4.1 IONIC BONDING AND STRUCTURE
By: Merinda Sautel Alameda Int’l Jr/Sr High School Lakewood, CO [email protected]
ESSENTIAL IDEA
Ionic compounds consist of ions held together in lattice structures
by ionic bonds.
NATURE OF SCIENCE (2.2)
Use theories to explain natural phenomena – molten ionic compounds conduct electricity
but solid ionic compounds do not. The solubility and melting points of ionic
compounds can be used to explain
observations.
THEORY OF KNOWLEDGE
General rules in chemistry (like the octet rule) often have exceptions. How
many exceptions have to exist for a rule to cease to be useful?
What evidence do you have for the existence of ions? What is the
difference between direct and indirect
evidence?
UNDERSTANDING/KEY IDEA 4.1.A
Positive ions (cations) form by metals losing valence
electrons.
UNDERSTANDING/KEY IDEA 4.1.B
Negative ions (anions) form by non-metals gaining
electrons.
An ion is a charged particle. Ions form when atoms gain or lose electrons.
A cation is a positive ion.
Formed when an atom loses one or more electrons.
An anion is a negative ion.
Formed when an atom gains one or more electrons.
The charge on an ion is equal to the number
of electrons gained or lost.
UNDERSTANDING/KEY IDEA 4.1.C
The number of electrons lost or gained is determined by
the electron configuration of
the atom.
CATIONS FROM GROUPS 1, 2 AND 3
Group 1 elements have one valence electron so they tend to lose one electron and form 1+ ions.
Group 2 elements have two valence electrons so they tend to lose two electrons and form 2+ ions.
Group 3 elements have three valence electrons so they tend to lose three electrons and form 3+ ions.
NOTICE THAT FOR IONS, THE CHARGE IS LISTED AFTER THE NUMBER (2+, 3-). OXIDATION STATES ARE LISTED WITH THE CHARGE BEFORE THE
NUMBER (+2, -3).
Group 4 elements do not tend to lose or gain
electrons due to the amount of energy involved so they do not normally form ionic bonds.
ANIONS FROM GROUPS 5, 6 AND 7
Group 15 elements have five valence electrons so they tend to gain 3 electrons and form 3-
ions.
Group 16 elements have six valence electrons so they tend to gain two electrons and form 2- ions.
Group 17 elements have seven valence
electrons so they tend gain one electron to form 1- ions.
ELECTRONS ARE GAINED OR LOST TO HAVE 8 ELECTRONS IN THEIR OUTER SHELL.
TRANSITION ELEMENTS
Transition elements have electron
configurations that allow them to lose different amounts of electrons from their d-sublevels.
They can form more than one stable ion.
The ions can be distinguished by color.
Here are some common examples:
Lead forms 4+ and 2+
Copper forms 2+ and 1+
Tin forms 4+ and 2+
Hydrogen can form the hydride H
-as well as H
+.
UNDERSTANDING/KEY IDEA 4.1.D
The ionic bond is due to the electrostatic attraction
between oppositely charged
ions.
IONIC CHARACTER
You can predict ionic character by two ways:
Position on the Periodic Table
Electronegativity differences
Position on the Periodic Table
Metals on the left side of the zigzag line tend to lose electrons.
Non-metals on the right side of the zigzag line tend to gain electrons.
The highest tendency to form ionic compounds will be between elements on the bottom left with elements on the top right.
Electronegativity
Electronegativity values are given in Table 8 of the IB Data Booklet.
Differences greater than 1.8 are considered to be ionic.
UNDERSTANDING/KEY IDEA 4.1.E
Under normal conditions,
ionic compounds are usually
solids with lattice structures.
LATTICE STRUCTURE
The ions in ionic compounds surround themselves with ions of the opposite charge.
Because of this, ionic compounds have three-dimensional crystalline structures known as ionic lattices.
The strength of force between the ions is known as
lattice enthalpy and depends upon the size of the ion and the charge on the ion.
The smaller the ion and the greater the charge, the higher the lattice enthalpy.
The coordination number expresses the number of ions that surround a given ion in the lattice.
The formula unit is the smallest particle of an ionic cmpd.
APPLICATION/SKILLS
Be able to explain the physical properties of ionic compounds (volatility, electrical
conductivity and solubility) in
terms of their structure.
PHYSICAL PROPERTIES
Remember physical properties can be
observed without chemically altering the substance.
MELTING AND BOILING POINTS
Ionic compounds have high melting and boiling points because the electrostatic attraction
between the ions is very strong and requires large amounts of energy to break the bond.
The higher the charge and smaller the ion, the
greater the melting point.
VOLATILITY
Volatility is the tendency of a substance to vaporize.
Ionic compounds have very low volatility.
SOLUBILITY
Solubility is the ease with which the solid dissolves in a liquid to become a solution.
Solubility trends are based on the similarity of the chemical nature of the solute and the
solvent.
Polar compounds dissolve in polar solvents.
Nonpolar compounds dissolve in nonpolar solvents
“Like dissolves like”
ELECTRICAL CONDUCTIVITY
Electrical conductivity is the ability to conduct electricity.
Freely moving ions must be present to conduct electricity.
Molten or dissolved ionic compounds conduct electricity.
Solid ionic compounds do not because the ions
are locked into place and are not free to move
about.
BRITTLENESS
Brittleness means the crystal will shatter when force is applied.
Ionic compounds tend to be brittle because
ions of like charge can be next to each other in
the lattice structure and the repulsive charges
cause the structure to split easily.
APPLICATION/SKILLS
Be able to deduce the formula and name of an ionic
compound from its
component ions, including
polyatomic ions.
GUIDANCE
Know these polyatomic ions:
NH
4+, OH
-, NO
3-, CN
-HCO
3-, CO
32-, SO
42-, PO
43-Citations
International Baccalaureate Organization. Chemistry Guide, First assessment 2016. Updated 2015.
Brown, Catrin, and Mike Ford. Higher Level Chemistry.
2nd ed. N.p.: Pearson Baccalaureate, 2014. Print.
ISBN 978 1 447 95975 5 eBook 978 1 447 95976 2
Most of the information found in this power point comes directly from this textbook.
The power point has been made to directly complement the Higher Level Chemistry textbook by Brown and Ford and is used for direct instructional purposes only.