1. 4.1 Ionic Bonding & Structure
Mrs. Page
IB Chem

2. Understandings
Positive ions (cations) form by metals losing valence electrons
Negative ions (anions) form by non-metals gaining electrons
The number of electrons lost or gained is determined by the electron configuration of the atom
The ionic bond is due to electrostatic attractions between oppositely charged ions.
Under normal conditions, ionic compounds are usually solids with lattice structures.

3. Application & Skills
Deduction of the formula and name of an ionic compound from its component ions, including polyatomic ions
Explanation of the physical properties of ionic compounds (volatility, electrical conductivity, and solubility) in terms of their structure.

4. Nature of Science
Use theories to explain natural phenomenon – 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.

5. Introduction to Bonding
Chemical bond: an interaction between atoms or ions that results in a reduction of the potential energy of the system, thereby becoming more stable
Three types of bonds: ionic, metallic, and covalent
The bond type depends on the atoms’ electronegativity values

6. More Bonding Basics
If the atoms have very different electronegativity values, then ionic bonding occurs
If they both have high electronegativity values, then covalent bonding occurs
If they both have low electronegativity values, then metallic bonding occurs

7. Practice: What Kind of Bond?
Na and Cl
Sr and O
C and O
Ni and Fe
N and O
Li and N
Ti and Cr
Ionic Covalent Metallic

8. Valence Electrons
Valence electrons are the electrons in the outermost energy level, which is the highest occupied energy level
They are the electrons responsible for the chemical properties of atoms
Electron transfers result in nobal gas electron configurations.
Core electrons – are those in the energy levels below.

9. Keeping Track of Electrons
Atoms in the same group have the same outer electronic structure and therefore the same number of valence electrons.
The number of valence electrons is easily determined. It is the group number
Group 2: Be, Mg, Ca, etc.
Each has 2 valence electrons

10. Electron Dot (Lewis Dot)diagrams
A way of showing & keeping track of valence electrons.
Write the symbol - it represents the nucleus and inner (core) electrons
Put one dot for each valence electron (8 maximum)
First two electrons placed as a pair (s orbital)
Then they don’t pair up until they have each have 1 (Hund’s rule) X

11. The Electron Dot Diagram (Lewis Structure) for Nitrogen
Nitrogen has 5 valence electrons to show.
First we write the symbol. N
Place 1st pair
Then add 1 electron at a time to each side.

12. The Octet Rule The noble gases are unreactive in chemical reactions
In 1916, Gilbert Lewis used this fact to explain why atoms form certain kinds of ions and molecules
The Octet Rule: in forming compounds, atoms tend to achieve a noble gas structure; 8 in the outer level is stable
Each noble gas (except He, which has 2) has 8 electrons in the outer level

13. Formation of Cations
Metals become oxidized (lose electrons) to attain a noble gas structure.
They make positive ions (cations)
If we look at the electronic structure, it makes sense to lose electrons:
Na: 2, 8, 1 shows 1 valence electron
Na1+: 2, 8 This is a noble gas structure with 8 electrons in the outer level.

14. Electron Dots For Cations
Metals have few valence electrons (usually 3 or less); calcium has only 2 valence electrons Ca

15. Electron Dots For Cations
Metals will lose the valence electrons Ca

16. Electron Dots For Cations
Form positive ions
Ca2+
This is named the “calcium ion”.
No dots are now shown for the cation.

17. Electron Configurations: Anions
Nonmetals are reduced (gain electrons) to attain noble gas electronic structures.
They make negative ions (anions)
S = 2,8,6 = 6 valence electrons
S2- = 2,8,8 = noble gas structure.
Halide ions are ions from chlorine or other halogens that gain electrons

18. Electron Dots For Anions
Nonmetals will have many valence electrons (usually 5 or more)
They will gain electrons to fill outer shell. 3- P
(This is called the “phosphide ion”, and should show dots)

19. Stable Electron Configurations
All atoms react to try and achieve a noble gas structure.
Noble gases have 8 valence electrons and so are already stable
This is the octet rule (8 in the outer level is particularly stable). Ar

20. Ionic Bonding
Anions and cations are held together by the electrostatic attraction due to the opposite charges (+ and -)
Simplest ratio of elements in an ionic compound is called the formula unit.
The bond is formed through the transfer of electrons (lose and gain)
Electrons are transferred to achieve noble gas structure.

21. Ionic Bonding Na Cl
The metal (sodium) is oxidized (loses its one electron) from the outer level.
The nonmetal (chlorine) is reduced (gains one electron) to fill its outer level, and will accept the one electron that sodium is going to lose.

22. [ ] Cl - Na+ Ionic Bonding Notes:
[ ]
Cl -
Na+
Notes:
Remember that no dots are now shown for the cation
Brackets must be shown in Lewis structures to show overall charge of ion
This step involving the formation of ions is a critical step to show in the formation of ionic bonds

23. Ionic Bond Negative charges are attracted to positive charges.
Negative anions are attracted to positive cations.
The result is an ionic bond.
A three-dimensional crystal lattice of anions and cations is formed.

24. Ionic Compounds
The ionic substance is held together by strong electrostatic attractions in all three dimensions
No molecules present
An ionic lattice-type structure is formed
This gives them distinct physical properties

25. NaCl
CsCl
TiO2

26. Properties of Ionic Compounds
Hard, brittle crystalline solids
Relatively high melting and boiling points
Do not conduct electricity when solid, but do when molten or in aqueous solution
Are more soluble in water than other solvents

27. - Page 198
The ions are free to move when they are molten (or in aqueous solution), and thus they are able to conduct the electric current.

28. Preserve Electroneutrality
When ions combine, electroneutrality must be preserved.
In the formation of magnesium chloride,
2 Cl- ions must balance a Mg2+ ion:
Mg Cl- → MgCl2

29. Predicting Ionic Charges
Group 1A:
Lose 1 electron to form 1+ ions H+
Li+
Na+ K+
Rb+

30. Predicting Ionic Charges
Group 2:
Loses 2 electrons to form 2+ ions
Be2+
Mg2+
Ca2+
Sr2+
Ba2+

31. Predicting Ionic Charges
Group 13:
B3+
Al3+
Ga3+
Loses 3 electrons to form 3+ ions

32. Predicting Ionic Charges
Nitride
Group 15:
P3-
Phosphide
As3-
Arsenide
Gains 3 electrons to form 3- ions

33. Predicting Ionic Charges
Oxide
Group 16:
S2-
Sulfide
Se2-
Selenide
Gains 2 electrons to form 2- ions

34. Predicting Ionic Charges
Group 17: F-
Fluoride
Br-
Bromide
Cl-
Chloride I-
Iodide
Gains 1 electron to form 1- ions

35. Predicting Ionic Charges
Stable noble gases do not form ions! Full octets.
Group 18:

36. Predicting Ionic Charges
Many transition elements
have more than one possible oxidation state.
Note the use of Roman numerals to show charges
Iron (II) = Fe2+
Iron (III) = Fe3+

37. Polyatomic Ions (MUST KNOW!)
Because these are ions they also are involved in ionic bonding!
Ion
Name
NH4+
ammonium
OH-
Hydroxide
NO3-
Nitrate
HCO3-
Hydrogen Carbonate
CO32-
Carbonate
SO42-
Sulfate
PO43-
Phosphate

38. Upcoming Dates: December 6 Final Exam Topics 1-3
HOMEWORK
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Upcoming Dates: December 6 Final Exam Topics 1-3