Topic 4.1: Chemical bonding and structure – Ionic bonding and structure
Ionic compounds consist of ions held together in lattice structures by ionic bonds.
• Understanding: Positive ions (cations) form by metals losing valence electrons.
▪ Positive ions (cations): ions formed by compounds/elements that loses its valence electrons (generally metal)
• Understanding: Negative ions (anions) form by non-metals gaining electrons.
▪ Negative ions (anions): ions formed by compounds/elements that gains its valence electrons (generally non-metal)
• Understanding: The number of electrons lost or gained is determined by the electron configuration of the atom.
▪ More than half of valence electrons: tend to gain electrons for a stable full valence shell
▪ Less than half of valence electrons: tend to lose electrons for a stable full valence shell
• Understanding: The ionic bond is due to electrostatic attraction between oppositely charged ions.
▪ Ionic bond: electrostatic attraction between a cation and an anion (oppositely charged ions)
• One or more electrons are transferred from one to another for a stable noble gas configuration
• Ionic bonds are not unidirectional and is spread out through the entire lattice
• Ionic bonds generally occur between metals and non-metals
• Understanding: Under normal conditions, ionic compounds are usually solids with lattice structures.
▪ Lattice-type structure: three-dimensional repeating units of positive and negative ions
• One sodium ion (blue) is associated with six chlorine ion (green) and vice versa
• In molecules, ions will be still very charged; thereby attracting more ions, and so forth
• Therefore the lattice is lower in energy (more stable) than it would be in separated molecules
Applications and skills: Deduction of the formula and name of an ionic compound from its component ions, including polyatomic
ions.
Name Ion Characteristic charge
Group 1 ions Na+, K+ 1+
Group 2 ions Ca2+, Mg2+ 2+
Group 17 ions F-, Cl- 1-
Ammonium NH4+ 1+
Hydroxide OH- 1-
Nitrate NO3- 1-
Hydrogen carbonate HCO3-, 1-
Carbonate CO32- 2-
Sulfate SO42- 2-
Phosphate PO43- 3-
▪ Deduction of the formula and name of an ionic compound
• The numerical sum of positive and negative charges must equal to 0.
• The name of the cation comes before the name of the anion
• Example: calcium nitrate (Ca(NO3)2); calcium has +2 charge, nitrate has -1 charge
Applications and skills: Explanation of the physical properties of ionic compounds (volatility, electrical conductivity and solubility)
in terms of their structure.
Property Ionic characteristics Description
Melting and boiling point High melting and Strong electrostatic forces of attraction in the lattice structure; large input of
boiling points energy is required to break these bonds
Volatility Low volatility (volatility: tendency of a substance to vaporize)
Low due to strong electrostatic force that prevents vaporization
Electrical conductivity Solid state: low In solids, the ions are fixed in a lattice and cannot conduct electricity (which
Molten state: high requires the free movement of ions or electrons); in dissolved and molten state,
Dissolved state: high the ions are free to move and are able to conduct electricity
Solubility Polar: soluble Molecules of water are polar and are partially charged on each side, hence can
Nonpolar: insoluble attract to ions to pull them out of the lattice to form a water shell; however in
(polarity of solvent) nonpolar solute, the ions are not attracted to solute and hence remain in position
• Nature of science: 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.
• Utilization: Ionic liquids are efficient solvents and electrolytes used in electric power sources and green industrial processes.
• Guidance: Students should be familiar with the names of these polyatomic ions: NH4+, OH-, NO3-, HCO3-, CO32-, SO42- and PO43-.
Ionic compounds consist of ions held together in lattice structures by ionic bonds.
• Understanding: Positive ions (cations) form by metals losing valence electrons.
▪ Positive ions (cations): ions formed by compounds/elements that loses its valence electrons (generally metal)
• Understanding: Negative ions (anions) form by non-metals gaining electrons.
▪ Negative ions (anions): ions formed by compounds/elements that gains its valence electrons (generally non-metal)
• Understanding: The number of electrons lost or gained is determined by the electron configuration of the atom.
▪ More than half of valence electrons: tend to gain electrons for a stable full valence shell
▪ Less than half of valence electrons: tend to lose electrons for a stable full valence shell
• Understanding: The ionic bond is due to electrostatic attraction between oppositely charged ions.
▪ Ionic bond: electrostatic attraction between a cation and an anion (oppositely charged ions)
• One or more electrons are transferred from one to another for a stable noble gas configuration
• Ionic bonds are not unidirectional and is spread out through the entire lattice
• Ionic bonds generally occur between metals and non-metals
• Understanding: Under normal conditions, ionic compounds are usually solids with lattice structures.
▪ Lattice-type structure: three-dimensional repeating units of positive and negative ions
• One sodium ion (blue) is associated with six chlorine ion (green) and vice versa
• In molecules, ions will be still very charged; thereby attracting more ions, and so forth
• Therefore the lattice is lower in energy (more stable) than it would be in separated molecules
Applications and skills: Deduction of the formula and name of an ionic compound from its component ions, including polyatomic
ions.
Name Ion Characteristic charge
Group 1 ions Na+, K+ 1+
Group 2 ions Ca2+, Mg2+ 2+
Group 17 ions F-, Cl- 1-
Ammonium NH4+ 1+
Hydroxide OH- 1-
Nitrate NO3- 1-
Hydrogen carbonate HCO3-, 1-
Carbonate CO32- 2-
Sulfate SO42- 2-
Phosphate PO43- 3-
▪ Deduction of the formula and name of an ionic compound
• The numerical sum of positive and negative charges must equal to 0.
• The name of the cation comes before the name of the anion
• Example: calcium nitrate (Ca(NO3)2); calcium has +2 charge, nitrate has -1 charge
Applications and skills: Explanation of the physical properties of ionic compounds (volatility, electrical conductivity and solubility)
in terms of their structure.
Property Ionic characteristics Description
Melting and boiling point High melting and Strong electrostatic forces of attraction in the lattice structure; large input of
boiling points energy is required to break these bonds
Volatility Low volatility (volatility: tendency of a substance to vaporize)
Low due to strong electrostatic force that prevents vaporization
Electrical conductivity Solid state: low In solids, the ions are fixed in a lattice and cannot conduct electricity (which
Molten state: high requires the free movement of ions or electrons); in dissolved and molten state,
Dissolved state: high the ions are free to move and are able to conduct electricity
Solubility Polar: soluble Molecules of water are polar and are partially charged on each side, hence can
Nonpolar: insoluble attract to ions to pull them out of the lattice to form a water shell; however in
(polarity of solvent) nonpolar solute, the ions are not attracted to solute and hence remain in position
• Nature of science: 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.
• Utilization: Ionic liquids are efficient solvents and electrolytes used in electric power sources and green industrial processes.
• Guidance: Students should be familiar with the names of these polyatomic ions: NH4+, OH-, NO3-, HCO3-, CO32-, SO42- and PO43-.
