Ionic Bonding

Pure Substances & Nomenclature Pure substances can exist in several forms: I) Atomic Elements & Molecular Elements, II) Ionic Compounds and III) Molecular Compounds (studied in next unit) I. - Atomic Elements & Molecular Elements: Some elements can exist as single atoms such as He, Ne, Cu, Hg, Au, Pb, U - Molecular Elements: Some elements exist in nature as diatomic molecules: H 2 N 2 O 2 F 2 Cl 2 Br 2 I 2 Know these Their names are the same as the element names Two elements are commonly polyatomic. Sulfur S 8 Phosphorous P 4

II. Ionic Compounds II. Ionic Compounds: These are compounds formed between ions. The metal loses electrons to become a + ion (Cation), and the nonmetal gains electrons to become a – ion (Anion). The + and – ions are attracted to each other in a ratio so that the resulting compound is neutral in charge; NaCl MgF 2 are examples. The formula unit is the simplest ratio of ions These have unique names formed from naming the + ion followed by the – ion with an “ide” ending.

“Perhaps one of you gentlemen would mind telling me just what is outside the window that you find so attractive..?” Image courtesy NearingZero.net

Valence electrons Are electrons in highest occupied energy level of an atom. For representative elements, number of valence electrons is the same as its group number. Ex. Lithium is in group 1A: has 1 valence electron Some transition metals form more than one ion. Ex. Fe 2+ and Fe 3+ Octet rule: atoms tend to achieve the electron configuration of a noble gas (8 electrons in outer energy level)by gaining or losing electrons.

elements of Group 2A have a +2 charge elements of Group 5A have a -3 charge elements of Group 6A have a -2 charge elements of Group 7A have a -1 charge The charge on an ion can be predicted from its position in the periodic table. Elements in Group 1A have a +1 charge

→ remove e - neutral atomcation If one or more electrons are removed from a neutral atom a positive ion is formed. A positive ion is called a cation.

Atomsodium (Na) calcium (Ca) lithium (Li)strontium (Sr) CationNa + Ca +2 Li + Sr +2 Name of Cation Sodium ion calcium ion Lithium ion strontium ion Naming Cations Cations are named the same as their parent atoms.

If one or more electrons are added to a neutral atom a negative ion is formed. A negative ion is called an anion. → neutral atom add e - anion

An anion consisting of one element has the stem of the parent element and an –ide ending Naming Anions

Atom Anion Name of Anion fluorine (F) F-F- fluoride ion stem

Atom Anion Name of Anion chlorine (Cl) Cl - Chloride ion stem

Atom Anion Name of Anion bromine (Br) Br - bromide ion stem

Atom Anion Name of Anion nitrogen (N) N 3- nitride ion stem

Atom Anion Name of Anion phosphorous (P) P 3- phosphide ion stem

Atom Anion Name of Anion oxygen (O) O 2- oxide ion stem

A chemical compound must have a net charge of zero. Writing Formulas From Names of Ionic Compounds If the compound contains ions, then the charges on all of the ions must add to zero.

Example: Aluminum Chloride Step 1: Step 2: Step 3: 13 Step 4: AlCl 3 Criss-Cross Method Al Cl write out name with space write symbols & value of charge of ions criss-cross charges as subsrcipts combine as formula unit (“1” is never shown) Aluminum Chloride

Example: Aluminum Oxide Step 1: Aluminum Oxide Step 2: Al 3+ O 2- Step 3: Al O 23 Step 4: Al 2 O 3 Criss-Cross Rule

Example: Magnesium Oxide Step 1: Magnesium Oxide Step 2: Mg 2+ O 2- Step 3: Mg O 2 2 Step 4: Mg 2 O 2 Step 5: MgO Criss-Cross Rule Use simplest ratios

Naming ionic compounds To name an ionic compound first write the name of the cation (+ ion) followed by the name of the anion (- ion)

Naming Binary Compounds FormulaName 1 BaO____________________ 2________________ sodium bromide 3 MgI 2 ____________________ 4 KCl____________________ 5________________ strontium fluoride 6________________ cesium fluoride barium oxide NaBr magnesium iodide potassium chloride SrF 2 CsF

Classwork: handout ionic binary compounds (single charge cations.)

A polyatomic ion is an ion that contains two or more elements. Naming Compounds Containing Polyatomic Ions

Al 2 (SO 4 ) 3 subscripts superscripts ALUMINUM SULFATE SO 4 2- Al 3+

Rules for Parentheses Parentheses are used only when the following two condition are met: 1.There is a polyatomic ion present and… 2.There are two or more polyatomic ions in the formula. Examples: NaNO 3 NO 3 1- is a polyatomic ion, but there is only one of it. Co(NO 3 ) 2 NO 3 1- is a polyatomic ion and there are two of them (NH 4 ) 2 SO 4 NH 4 1+ is a polyatomic ion and there are two of them; SO 4 2- is a polyatomic ion but there is only one of it.