CHAPTER 3 IONIC COMPOUNDS
Formation of Ions
Cations:
Overall positive electrical charge.
Number of protons ( {#protons}) is not equal to the number of electrons ( {#electrons}).
Has the same number of protons.
Formed by the loss of electron(s).
Anions:
Overall negative electrical charge.
Number of protons is not equal to the number of electrons.
Has the same number of protons.
Formed by the gain of electron(s).
Atoms:
Overall no electrical charge.
Number of protons equals the number of electrons.
Number of protons equals atomic number.
The Octet Rule
Definition: Atoms without a closed valence shell or an octet of electrons in their valence shell tend to combine in compounds in order to attain a closed shell or an octet of electrons.
Mechanism: A closed shell or octet can be attained by an atom losing, gaining, or sharing valence electrons with another atom.
Common Ionic Charges of Selected Elements
Octet rule: Elements tend to react in such a way as to attain the electron configuration of the noble gas nearest to them in the periodic table.
IONIZATION
Cation Formation: All metals form which type of cations.
Nonmetals tend to form anions.
Cations are formed by the loss of valence electrons.
Group 1A metals lose 1 electron from each neutral atom.
Group 2A metals lose 2 electrons from each neutral atom.
Question: Based on the charge on the ions, we can tell about the directional relationship with their group number.
Periodic Trends
Trends: Ionization Energy
Definition: Ionization energy is the energy needed to remove an electron from a neutral atom.
Ionization energies decrease down a column as the valence electrons get farther away from the positively charged nucleus.
Ionization energies increase across a row as the number of protons in the nucleus increases.
Visual examples: Ionization energies change across different groups (1A to 8A) and with various elements.
Metallic Character
Increase: The metallic character increases when an element can lose its valence electrons more easily, it increases down a group.
Decrease: Metallic character decreases across a period because electrons are harder to remove from atoms with more protons.
Periodic Table Trend Summary
Property | Top to Bottom | Left to Right |
|---|---|---|
Valence Electrons | Remains the same | Increases |
Atomic Radius | Increases | Decreases |
Ionization Energy | Decreases | Increases |
Metallic Character | Increases | Decreases |
Learning Check
Select the element in each pair with higher ionization energy:
Li or K
K or Br
P or Cl
Solutions:
Li is higher than K.
Br is higher than K.
Cl is higher than P.
Electron Configuration of Ions
Cations and Anions
Example Cations:
Ca (20 electrons): Noble Gas Notation [Ar]4s²
Rb (37 electrons): Noble Gas Notation [Kr]5s¹
Ca²⁺ (18 electrons): [Ar]
Rb⁺ (36 electrons): [Kr]
Example Anions:
Cl (17 electrons): [Ne]3s²3p⁵
Cl⁻ (18 electrons): [Ar]
S (16 electrons): [Ne]3s²3p⁴
S²⁻ (18 electrons): [Ar]
Large Ions and d-block Ions
d-block elements maintain a closed shell of electrons to satisfy the octet rule.
When a transition metal forms a cation, it will first lose the electrons from the preceding s shell and then the d shell.
Example with Iron: Fe: [Ar]4s²3d⁶, Fe³⁺: [Ar]3d⁵
Transition Metals
Transition metals like cobalt can form several different charges (oxidation states).
Cobalt: Co: [Ar]4s²3d⁷, Co²⁺: [Ar]3d⁷, Co³⁺: [Ar]3d⁶.
Important Note: When d-block elements form ions, the 4s electrons are lost first before losing 3d electrons.
Ionic Compounds
Introduction to Bonding
Bonding is the joining of two atoms in a stable arrangement.
Types of Bonds:
Ionic bonds: Result from the transfer of electrons from one element to another.
Covalent bonds: Result from the sharing of electrons between two atoms.
Ionic and Covalent Bonds
Atoms form octets to achieve more stability.
Covalent Compounds
Formed by nonmetals sharing valence electrons.
Examples: Water (H₂O), Carbon Dioxide (CO₂), Glucose (C₆H₁₂O₆).
Ionic Compounds
Formed when metal atoms transfer electrons to nonmetal atoms.
Everyday examples: Table salt (NaCl), Baking soda (NaHCO₃), Milk of magnesia (Mg(OH)₂).
Is the Substance Ionic or Covalent?
Ionic: Contains both metal and non-metal atoms.
Sample Problem: Bond Type Prediction
Determine whether compounds are ionic or covalent based on metal/nonmetal location in the periodic table.
a. NaI (ionic)
b. H₂O₂ (covalent)
Definition: Molecule
A molecule is a discrete group of atoms that share electrons.
Example: Hydrogen molecule (H₂) has two hydrogen atoms sharing electrons.
Physical Properties of Ionic Compounds
Ionic compounds are:
Crystalline solids
Very high melting points (e.g., sodium chloride at 801°C)
Extremely high boiling points (e.g., sodium chloride at 1413°C)
Water-soluble
When dissolved in water, they dissociate into cations and anions, conducting electric currents (electrolytes).
Recap of Ionic Compounds
Composed of oppositely charged ions.
Illustrate the octet rule where metals lose electrons and nonmetals gain electrons.
Relation of Group Number to Ionic Charge
Metals: Form cations; group number equals the charge on the cation for Groups 1A, 2A, 3A.
Nonmetals: Form anions; for Groups 6A and 7A, anion charge equals 8 minus the group number.
Example of Electron Configuration Summary
Group 1A: 1+
Group 2A: 2+
Group 3A: 3+
Group 6A: 2-
Group 7A: 1-
Dietary Ions
Ca²⁺ found in teeth and bones.
Fe²⁺ found in blood hemoglobin.
Na and K⁺ in body fluids.
Cl⁻ in gastric juices and other fluids.
Mg²⁺ required for nerve transmission and muscle control.
Limits on Sodium Intake
FDA recommends no more than 2,300 mg of sodium per day (approx. one teaspoon).
High consumption risks: High blood pressure, heart disease, kidney disease, stroke.
Formulae for Ionic Compounds
The sum of the charges in an ionic compound must equal zero.
Example Calculation: Calcium Fluoride
CaF₂ composition has 1 Ca²⁺ to 2 F⁻, maintaining charge neutrality.
How to Name Ionic Compounds
Identify grouping at elements and differentiate between cations and anions.
Use the appropriate nomenclature for naming based on cation and anion types.
Regular naming conventions for ionic compounds apply (no need to state the anionic charge except for variable charge metals).
Reminder of Transition Metals Naming
Use roman numerals to indicate charge:
Example: Fe²⁺ - Iron(II)
Example: Fe³⁺ - Iron(III)
Polyatomic Ions
A