Ionic Bonding: Formation and the Octet Rule

Ionic Bonding Basics

• Involves the transfer of one or more electrons between atoms, leading to the creation of ions
• This transfer results in ions, atoms with a net positive or negative charge

Formation of Ions

• One atom loses electrons and becomes positively charged (cation)
• Another atom gains electrons and becomes negatively charged (anion)
• Oppositely charged ions attract, forming an electrostatic bond known as an ionic bond

Octet Rule

• Predicts that atoms tend to gain, lose, or share electrons to achieve a stable electron configuration
• Stable electron configurations are similar to those of noble gases
• Noble gasses such as Helium or Neon have filled outer shells of electrons
• Atoms achieve a stable configuration by gaining or losing electrons to attain a full outer shell in ionic bonding

Metals vs Nonmetals

• Metals typically lose electrons to achieve the nearest noble gas configuration
• Nonmetals typically gain electrons to achieve the nearest noble gas configuration
• The valence electrons are the electrons in the atom's outermost shell

Sodium Chloride Formation

• NaCl (Sodium Chloride) forms through ionic bonding
• Sodium (Na) has one electron in its outer shell, and chlorine (Cl) has seven
• Atoms achieve a stable electron configuration by losing and gaining electron,
• Sodium achieves the configuration of neon by losing one electron, becoming Na+ (sodium ion)
• Chlorine achieves the configuration of argon by gaining one electron, becoming Cl- (Chloride ion)
• The resulting attraction between the oppositely charged ions results in the ionic bond in sodium chloride

Ionic Compounds

• Ionic compounds are molecules made up of ions that form charged particles in order to gain or lose electrons

Definition of Ionic Compounds

• Chemical compounds composed of positively charged ions (cations) and negatively charged ions (anions)
• They are held together by the electrostatic attraction between oppositely charged ions
• They are formed when one or more electrons are transferred from a metal atom to a nonmetal atom
• The forces of electrostatic attraction in a compound cause ions to surround themselves with oppositely charged ions
• As a result, ionic compounds take on a predictable 3D crystalline structure known as ionic lattice

Naming Ions

• A monatomic ion is a single atom with a charge
• For single-atom cations (positive ions), the name is the same as the atom, followed by "ion"
  • Lithium ion = Li+
  • Calcium ion = Ca2+
• To name negative ions, take the element name from the periodic table, replace the ending with "ide" and then "ion"
  • Sulfide ion = S2-
  • Bromide = Br1-
• Ionic charge of an element is found from the periodic table

Ionic Charge on the Periodic Table

• Metals on the left will is positive, non-metals on the right will be negative
• Group IA (1): Loses 1 electron to form 1+ ions, like H+, Li+, Na+, K+
• Group IIA (2): Loses 2 electrons to form 2+ ions, like Be2+, Mg2+, Ca2+, Sr2+, Ba2+
• Group IIIA Loses 3 electrons to form 3+ ions, B3+, Al3+, 3+
• Group IVA will share electrons and not form ions
• Group VA (15): Gains 3 electrons to form 3− ions - Nitride N3−, Phosphide P3−, Arsenide As3−
• Group VIA (16): Gains 2 electrons to form 2− ions - Oxide O2−, Sulfide S2−, Selenide SE2−
• Group VIIA (17): Gains 1 electron to form 1- ions - Fluoride F-, Chloride Cl−, Bromide Br−
• Group VIIIA is stable and noble gasses do not form ions

Transition Metals

• Group B (3 - 12) transition elements have more than one possible oxidation state.
  • Iron(II) = Ferrous = Fe2+
  • Iron(III) = Ferric = Fe3+

Naming Ionic Compounds

• Examples include:
  • Potassium Chloride = KCI = K+ and CI-
  • Magnesium Fluoride = Mg(F)2 = Mg2+ and F-
  • Copper (II) Chloride = Cupric Chloride = CuCl2 = Cu2+ and Cl-
  • Sodium Bromide = NaBr = Na+ and Br-
  • Sodium Sulfide = Na2S = Na+ and S2
  • Iron (III) Chloride = Ferric Chloride = FeCl3 = Fe3+ and Cl−
  • Zinc Sulfide = ZnS = Zn2+ and S

Oxidation

• Oxidation is a chemical reaction where a substance loses electrons
• Oxidation often involves adding oxygen or removing hydrogen
• Oxidation increases an atom's oxidation state

Oxidation State

• Indicated the apparent charge of an atom within a molecule/ion
• Helps keep track of electron transfers in chemical reactions

Polyatomic Ion

• A covalently bonded set of two or more atoms, or of a metal complex
• Behave as a single unit and has a net charge that is not zero.

Writing Ionic Compound Formulas

• Write formulas for the cation and anion, including charges
• Check to see if charges are balanced
• Balance charges (using subscripts), using parenthesis if you need more than one polyatomic ion.
• Writing steps exemplified by:
  • Potassium Iodide; K+ and I- are balanced so the formula is KI
  • Iron(III) Chloride; Fe3+ and Cl- are unbalanced so the formula is FeCl3
  • Aluminum Sulfide; Al3+ and S2- are unbalanced so the formula is Al2S3