Ch 5 Ions and Ionic Compounds What is the difference between an atom and an ion? How can an atom become and ion? Why do chemists call table salt sodium chloride? Why do chemists write the formula for sodium chloride as NaCl?

Simple Ions Chemical reactivity – differs based on electron configuration Noble gases - least reactive, complete outer energy levels Octet rule – other elements match s and p electron config of noble gases Alkali metals and Halogens most reactive one electron away from noble config

Valence Electrons Periodic table has valence electrons config Atoms gain or lose electrons to become ions -become charged Cation has a positive charge loses electrons Anion has a negative charge gains electrons

Some ions with noble gas configs –p162

Ions that do not have noble gas configs Transition metals form ions without complete octets Most form more than one type of ion

Atoms and ions Properties differ Sodium chloride form Na+ and Cl- in water both very different properties from atoms

Ionic Bonding and Salts bond formed by the attraction between oppositely charged ions cations(+) and anions(-) opposite charges attract One atom is strong enough to pull an electron away from another atom and keep it. This creates the ions which are then attracted to each other. + -

Transferring Electrons Energy is required to transfer electrons Forming a salt is exothermic and endothermic Formation of ions endothermic Formation of solid from ions is exothermic

Formation of Sodium Chloride

Ionic Compounds Ionic compounds do not consist of molecules Ionic bonds are strong Bonding between metals and non-metal Metal atoms have a low number of valence electrons and a low electronegativity. Non-metal atoms have numerous valence electrons. If the electron clouds overlap (bond)..

Metals lose valence electrons achieve a stable valence shell Metals    lose valence electrons    achieve a stable valence shell (usually 8 e-)    gains a positive charge, ie a positive ion. The charge is the number of valence e- it has to lose Non-metals gain valence electrons achieve a stable valence shell (usually 8 e-)

Characteristics of Ionic Compounds Crystalline solids at room temperature hard and brittle Have higher melting points and boiling points compared to covalent compounds Conduct electrical current in molten(liquid) or solution state Are extremely polar bonds Most are soluble in water but not soluble in non-polar solvents

Sodium Chloride in Three Phases

Salt Crystals Arranged in crystal lattice Crystal structure depends on size and ration of ions Smallest repeating unit is a unit cell                          Calcite Fluorite Halite

Naming Ionic Compounds Simple Cations -name of the element Cu+ copper (I) Cu2+ copper(II) Simple Anions – name of the element ends in –ide Cl- chloride Binary compounds- name of cation plus name of anion CuCl2 Copper (II) chloride

Writing Ionic Formulas No overall charges Ion charges must balance Iron (III)oxide Fe 3+ O2- 2 x Fe3+ = 6+ 3 x O2- = 6- (6+) + (6-) = 0 Fe2O3 Fe 3+ O2- Fe2O3

Naming polyatomic ions Ions made of two or more atoms Charged group Table on p 178 -ite -ate have oxygen in them K2CO3 K+ potassium CO32- carbonate Potassium carbonate