Ionic Bonding (6.1)

Review Valence Electron - an electron that is in the highest occupied energy level of an atom Key role in chemical reactions The number of the group matches the number of valence electrons Elements in a group have similar properties because they have the same number of valence electrons

Stable Electron Configurations When the highest occupied energy level of an atom is filled with electrons, the atom is stable and not likely to react Nobel gases have stable electron configurations with eight valence electrons (helium only has two) The chemical properties of an element depend on the number of valence electrons

Electron Dot Diagram Model of an atom in which each dot represents a valence electron The symbol at the center represents the nucleus and all other electrons in the atom

Ionic Bonds Some elements achieve stable electron configurations through the transfer of electrons between atoms

Transfer of Electrons Chlorine is one electron short of having 8 valence electrons Sodium has one too many electrons to be stable Sodium transfers its “extra” electron to chlorine to make both atoms more stable

Formation of Ions When an atom gains or loses electrons its charge is no longer neutral Ion - an atom that has a net positive or negative electric charge Anion - an ion with a negative charge Named by using part of the element name plus the suffix -ide Example: Cl- is called a chloride ion Cation - an ion with a positive charge Named by using the element name Example: Na+ is called a sodium ion

When an anion and cation are close together the form chemical bonds because opposite charges attract Chemical Bond - the force that holds atoms or ions together as a unit Ionic Bond -the force that holds cations and anions together Form when electrons are transferred from one atom to another

Ionization Energy Amount of energy used to remove an electron from an atom of an element The energy allows the electrons to overcome the attraction of the protons in the nucleus Varies from element to element The lower the ionization energy, the easier it is to remove an electron from an atom

Ionic Compounds Compounds that contain ionic bonds Chemical Formula - a notation that shows what elements a compound contains and the ratio of atoms or ions of these elements in the compound Examples: Sodium chloride is NaCl Magnesium chloride is MgCl2 Subscript is used to show the relative numbers of atoms of the elements present. If there is only one atom of an element in the formula no subscript is used

Crystal Lattices Repeating pattern of ions in fixed positions Crystals - solids whose particles are arranged in a lattice structure Classified into groups based on the shape of their crystals The arrangement of the ions depends on the ratio of ions and their relative sizes

Properties of Ionic Compounds The properties of an ionic compound can be explained by the strong attractions among ions within a crystal lattice Properties High melting point because of strong attractions between particles = more energy needed to separate them Poor conductor of electricity as solids because of the structure but good conductors as liquids Crystals shatter when struck because the like charged ions repel each other