Ionic Bonding

• Chemical bond


  The attractive force that holds two atoms together in a more complex unit
• Valence electron


  An electron in the outermost electron shell of a representative element or noble-gas element that is important in determining the bonding characteristics of a given atom
• Generalizations about valence electrons

  • Representative elements in the same group of the periodic table have the same number of valence electrons
  • The number of valence electrons for representative elements is the same as the Roman numeral periodic-table group number
  • The maximum number of valence electrons for any element is eight
• Lewis symbol


  The chemical symbol of an element surrounded by dots equal in number to the number of valence electrons present in atoms of the element
• Octet rule


  In forming compounds, atoms of elements lose, gain, or share electrons in such a way as to produce a noble-gas electron configuration for each of the atoms involved
• Ionic bond


  A chemical bond formed through the transfer of one or more electrons from one atom or group of atoms to another atom or group of atoms
• Ionic compound


  A compound in which ionic bonds are present
• Ion


  An atom that is electrically charged as a result of the loss or gain of electrons
• Anion


  A negatively charged ion where electrons outnumber protons
• Cation


  A positively charged ion where protons outnumber electrons
• Generalizations about ionic charges

  • Metal atoms containing one, two or three valence electrons tend to lose electrons to acquire a noble-gas electron configuration
  • Nonmetal atoms containing five, six, or seven valence electrons tend to gain electrons to acquire a noble-gas electron configuration
  • Elements in Group IVA would have to gain or lose four electrons to attain a noble-gas structure
• Monatomic ion


  An ion formed from a single atom through loss or gain of electrons
• Polyatomic ion


  An ion formed from a group of atoms (held together by covalent bonds) through loss or gain of electrons
• Cation naming

  Cations formed from metal atoms have the same name as the metal<|>If a metal can form different cations, the charge on the metal ion is incorporated into the name by a Roman numeral in parentheses or the endings -ous/-ic are used
• Anion naming


  Monatomic anions are formed by replacing the ending of the name of the element with -ide<|>Polyatomic ions containing oxygen (oxyanions) have names ending in -ate or -ite, with prefixes -per and -hypo indicating more or fewer oxygen atoms
• Ionic compounds are always neutral, with the ratio of positive and negative ions combining to achieve charge neutrality
• Rules for writing ionic compound formulas

  • The symbol for the positive ion (cation) is always written first
  • The charges on the ions that are present are not shown in the formula
  • The number of each type of ion present is the smallest whole number ratio that results in a neutral compound
• Oxyanion


  Oxygen-containing anion
• ClO4-


  Perchlorate ion (one more O atom than chlorate ion)
• ClO3-

  Chlorate ion
• ClO2-


  Chlorite ion (one O atom fewer than chlorate)
• ClO-


  Hypochlorite (one O atom fewer than chlorite)
• Ionic compounds are always neutral
• Electron loss always equals electron gain in an electron transfer process
• The ratio in which positive and negative ions combine is the ratio that achieves charge neutrality for the resulting compound
• Rules for writing chemical formulas for ionic compounds

  • The symbol for the positive ion (cation) is always written first
  • The charges on the ions that are present are not shown in the formula
  • The numbers in the formula (subscripts) give the combining ratio for the ions
• Ionic compounds with metals with variable charges

  The charge on the metal ion must be incorporated into the name using Roman numerals
• If you are uncertain about the charge on the metal ion in an ionic compound, use the charge on the nonmetal ion (which does not vary) to calculate it
• Conventions for writing chemical formulas containing polyatomic ions


  • When more than one polyatomic ion of a given kind is required in a chemical formula, the polyatomic ion is enclosed in parentheses, and a subscript, placed outside the parentheses, is used to indicate the number of polyatomic ions needed
  • The same elemental symbol may be used more than once in a chemical formula so that the identity of polyatomic ions is preserved
• Rules for naming ionic compounds containing polyatomic ions

  • If the polyatomic ion is positive, its name is substituted for that of the metal
  • If the polyatomic ion is negative, its name is substituted for the nonmetal stem plus -ide
  • When both positive and negative ions are polyatomic, dual substitution occurs, and the resulting name includes just the names of the polyatomic ions
• Ionic compounds containing polyatomic ions


  • K2CO3 (potassium carbonate)
  • Fe2(SO4)3 (iron (III) sulfate)
  • NH4Cl (ammonium chloride)
  • (NH4)2SO4 (ammonium sulfate)
• Structure of ionic compounds in the solid state

  • Positive and negative ions are arranged in a way that maximizes attractions between ions of opposite charge and minimizes repulsions between ions of like charge
  • The specific arrangement depends on ion sizes and the ratio between positive and negative ions
  • Arrangements are usually very symmetrical and result in crystalline solids
• Properties of ionic compounds

  • They have very high melting and boiling points
  • Compounds in solid state are nonconductors of electricity
  • In liquid or molten state, ionic compounds can conduct electricity
• In solid state, the ions occupy fixed positions in the crystal lattice and vibrate in their fixed positions
• In liquid or molten state, or when in solution, ions are able to move about and carry a charge, resulting in electrical conductivity
• Electron Loss


  Process of losing or giving away one or more electrons
• Electron Gain


  Process of gaining or obtaining one or more electrons
• Electron Loss = Electron Gain


  In an electron transfer process, loss of electrons always equals gain of electrons
• Conservation of Charge


  Electron loss and gain are always equal to maintain charge balance