Ions and the Octet Rule

• Ionic compounds feature positive and negative ions attracting each other.
• In solids, these ions form rigid crystalline lattices.
• Melting requires significant thermal energy due to strong attractions.
• Once melted, they conduct electricity because of mobile ions.
• Ions interact with polar water molecules, often making the compounds water-soluble.

Key Understandings of Ionic Structures

• Metal atoms lose electrons to form positive ions (cations).
• Non-metal atoms gain electrons to form negative ions (anions).
• Ionic bonds result from electrostatic attraction between oppositely charged ions.
• Binary ionic compounds are named with the cation first, followed by the anion using the suffix "ide".
• Ionic compounds form 3D lattice structures represented by empirical formulas.

Introduction to Bonds and Structures

• Atoms connect in diverse ways, either with the same or different elements.
• Arrangements and bond features cause different properties.
• Chemical bonds hold atoms, specifically ionic, covalent, and metallic bonds.
• These bonds lead to four structure types: ionic, molecular covalent, covalent network, and metallic.
• Covalent substances exist as continuous 3D networks or discrete molecules.

Models

• Scientific models simplify and represent complex phenomena like bonding.
• An important reason for applying bonding models is the ability to visualize what we cannot observe directly.
• All models have limitations that need to be understood.

Chemical Bonds

• These represent strong attractions holding atoms/ions together.
• All chemical bonds occur due to attractions between positive and negative species.
• The type is reliant on the species involved.

Understanding Types of Bonding

• Ionic: Cations attract anions.
• Covalent: Atomic nuclei attract a shared pair of electrons.
• Metallic: Cations attract delocalized electrons.

Ions

• Sodium chloride and copper(II) sulfate exemplify ionic compounds.
• They are crystalline and brittle, a characteristic of ionic compounds.
• As solids, they're poor conductors, but molten/dissolved, they conduct well.
• The reactions/properties differ from their elements.
• Sodium chloride is water-soluble.
• Elemental sodium is a reactive metal, and chlorine is a poisonous gas.

Cations and Anions

• Sodium chloride has sodium ions, not atoms, which behave differently.
• Three differences exist between sodium atoms (Na) and ions (Na+).
• These are number of electrons, electron arrangement, and charge.
• Sodium atoms are neutral, while ions have a 1+ charge (Na+).
• Ions with more protons than electrons are cations with positive charges.
• Ions with more electrons than protons are anions with negative charges.

Predicting Ion Charges

• Main group elements in groups 1, 2, 13, 15, 16, and 17 form predictable ions.
• Examples: Na (1s²2s²2p⁶3s¹) becomes Na+ (1s²2s²2p⁶) by losing an electron.
• Species sharing electron configuration are isoelectronic.
• Cations achieve noble gas configurations by losing valence electrons.
• This loss makes them positively charged.
• Anions form by gaining electrons to achieve noble gas configuration, becoming negatively charged.
• Chlorine gains an electron instead of losing seven to achieve the configuration.
• Formation is a reduction process, while cation formation is oxidation.
• The formation of an ionic compound from its elements involves a redox reaction: 2Na(s) + Cl₂(g) → 2NaCl(s).
• Atoms achieve noble gas electron configurations by gaining/losing/sharing electrons.
• Often referred to as the octet rule.
• Main group elements relate to ion charge by group number.
• Groups 1, 2, and 13 form 1+, 2+, and 3+ ions, respectively.
• Groups 15, 16, and 17 form 3−, 2−, and 1− ions, respectively.
• Hydrogen forms H+ (proton) or H- (hydride) ions.
• High charge density in H+ allows easy bonding with other species.

Transition Elements

• They have partially filled d sublevels
• Can form multiple ions with varied charges.
• Ionization involves losing 4s electrons before 3d.
• Variable oxidation states are due to similar 4s and 3d sublevel energies.
• Successive ionization energy data helps study variable oxidation states.

Electronegativity

• Measure of atom's ability to attract covalently bonded electrons
• Used to estimate bond ionicity.
• Values are on the Pauling scale from 0.8 to 4.0.
• Ionic bonding occurs when electronegativity above 1.8.

Periodic Table Position and Ion Character

• Elements with large electronegativity differences are at greater horizontal distances in the periodic table.

Polyatomic Ions

• Some ionic compounds contain more than two elements.
• Polyatomic ions contain several atoms.
• Ammonium ions (NH₄⁺) are polyatomic.

Naming Ionic Compounds

• The cation name is given as the first, which is further followed by the anion name
• Cations adopt the name of the parent atom, which remains unchanged
• Monatomic anions get first part of the parent atom name, + "ide"
• The name doesn't reflect ion numbers

Formulas

• The name indicates elements but not the ratio.
• Net charge is zero, balancing positive and negative charges.
• The criss-cross rule is a method that swaps the charges and turns them subscript.

Ionic Lattices and Properties

• Within ionic crystals, ions are arranged in a lattice structure.
• Lattices are continuous, three-dimensional units of positive and negative ions.
• The formula is an empirical one, showing the ratio of each ion type.
• Ionic bonds are non-directional, where each ion attracts oppositely charged ions around it..

Lattice Enthalpy

• This shows the measure of the strength of attraction in the lattice.
• It is endothermic, or formation of gaseous ions from a solid lattice.
• Affected by ionic radius and charge.
• Strength of electrostatic attraction increases as ionic charge increases.

Volatility

• Refers to the tendency of a substance to vaporize (turn into a gas)
• It is very low in ionic compounds
• It reflects high boiling points
• Electrical conductivity is possible if substances move around their lattice structure
• Cations and Anions vibrate, but can’t change position

Solubility

• Ionic compounds generally dissolve easily in polar liquids such as water.
• But, do not dissolve easily in non-polar solvents such as hexane.