 Chemical Reactivity – How much an element reacts depends on the electron configuration of its atoms. › Ex: O and Ne  Noble gases are least reactive.  Alkali metals and halogens are most reactive. WHY?

 Group number tells you how many electrons are in an element’s valence shell.  Atoms gain and lose electrons to become stable.

 An atom and its ion have different chemical properties. › Stable ion should not be confused with noble gas  Has a charge now and forms a compound.

 Atoms of metals & nonmetal elements form Ions differently. › Almost all metals form cations  Ex: Mg – 1s2 2s2 2p6 3s2  Takes less energy to lose 2 electrons, than gain 6.  Nonmetals form anions › Ex: O – 1s2 2s2 2p4 › Gaining 2 electrons requires less energy than losing 6.

 Form between ions of opposite charges (+ & -). › Compound becomes electrically neutral. › Ex: NaCl

 Ionization energy – energy needed to remove the outermost electron from an atom.  Endothermic – Needs energy to be put in the reaction in order for the reaction to occur.  Exothermic – Reaction releases energy (often heat).

 Strong  Have high melting/boiling points  Rarely gas at room temp.  When dissolved conduct electric current.  Salts are hard and brittle.

 Simple Ions: › Cation borrows name of element: K is potassium ion. › When element forms 2+ ions, roman numerals are used:  Ex: Cu+ : copper (I) ion  Cu 2+ : copper (II) ion › Anion also uses element name but, add ide to end.  Ex: chloride, oxide

 Cation name followed by anion › Ex: NaCl sodium chloride › Ex: Mg3N2 magnesium nitride › Ex: K2 potassium oxide

 Must have no overall charge (neutral). › Ex: Mg 2+ and N3-

 Presence of Oxygen – ite and -ate. The one with less O is ite, while the one with more O is ate. › Ex: SO 3 2- is sulfite SO 4 2- is sufate

 Presence of hydrogen indicated by using hydrogen.  Prefixes are used to indicate how many hydrogen › Ex: H 2 PO 4 2- : dihydrogen phosphate.  MUST KNOW: CO 3 2-, OH -, NO 3 -, NO 2 -, phosphate, sulfate, sulfite.

 K 2 CO 3  Name cation: name of the element.  Name anion: what is the charge?  Write it out  Potassium carbonate