Ionic Compounds Naming and Writing Formulas Chemistry II Ionic Compounds Naming and Writing Formulas

Review of how ions are formed Octet rule – elements are most stable when they have 8 valence electrons Elements can gain or lose valence electrons in order to have 8.

Formation of Cation sodium atom Na sodium ion Na+ 11p+ 11p+ e- e- e- loss of one valence electron 11p+ e- e- e- e- e- e-

Formation of Anion chlorine atom chloride ion Cl1- Cl 17p+ 17p+ e- gain of one valence electron e- e- e- e- e- e- e- e- 17p+ e- e- e- e- e- e- e- e- e- e-

Bonding Chemical Bond attractive force between atoms or ions that binds them together as a unit Purpose bonds formFORM IN ORDER TO …. To decrease potential energy (PE) To Increase stability Atoms in all substances that contain more than one atom are held together by electrostatic interactions—interactions between electrically charged particles such as protons and electrons. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Why bonds form… Atoms of many elements are more stable as they are bonded to other atoms. Energy is released into surroundings resulting in a system with lower energy. An atom’s electron configuration determines how it interacts with other atoms Particularly valence electrons

What are ionic bonds? Chemical interactions(attractions) between charged particles - Called Electrostatic attraction Result from a transfer of electrons making a cation and anion

Crystal Lattice NaCl 1:1 Ratio Strong Attractions within a crystal lattice. Remember the atoms transfer the electrons and then are attracted to each other because of opposite charges Ionic compounds do not exist as single molecules but rather as numerous units organized in a stable crystal .

Participants Ionic bonds form between metals and non-metals Metals have lower ionization energies and therefore more readily “give away” electrons – Form Cations Non-metals have high electron affinities and therefore more readily accept electrons. – Form Anions New Term- Oxidation Number = ion charge sodium’s oxidation number is 1+, Chlorine’s is 1-

Naming Ionic Compounds Cation – borrows name from element Always listed first Anion – ends in “ide” (with the exception of polyatomic ions) Always listed second Examples NaCl – sodium chloride ZnS – zinc sulfide Mg3N2 – magnesium nitride SPELLING COUNTS!

Example: Aluminum Chloride Writing Ionic Formulas Criss-Cross Rule Example: Aluminum Chloride Step 1: Write symbols & charge of elements. Write charges ABOVE the letters Al Cl 3+ 1- Step 2: Al Cl criss-cross charges as subscripts 1 3 http://upload.wikimedia.org/wikipedia/commons/4/42/Aluminium-trichloride-3D-structures.png Step 3: AlCl 3 combine as formula unit *“1” is never shown *get rid of charges on top Step 4 : *simplify if needed

Variable Charge Ions Some elements in the transition metals can form more than one type of ion. Sometimes they may lose 2, 3, 4 or even more electrons in order to bond with another element. So these metals can form +2, +3 ,+4 etc cations in one compound but have a different charge in another compound. In order to tell them apart we name them differently.

Writing the formula When given the name of the compound, the Roman numeral after the metal tells us the CHARGE of the metal. Copper II Chloride – means Cu+2 Cl-1 Follow the same steps as before >>>> 1. Write out the charges 2. Criss-cross 3. Combine as a formula unit (get rid of charges on top) 4. Simplify if needed

A. To name, given the formula: Cu Fe Figure out charge on cation. 2. Write name of cation. 3. Write Roman numerals in ( ) to show cation’s charge. Stock System of nomenclature 4. Write name of anion. FeO iron oxide Fe? Fe2+ O2– iron (II) oxide Fe2O3 Fe? iron oxide Fe3+ Fe? Fe3+ O2– O2– O2– iron (III) oxide CuBr copper bromide Cu? Cu1+ Br1– copper (I) bromide CuBr2 Cu? copper bromide Cu2+ Br1– Br1– copper (II) bromide

When writing the formula for an ionic compound with a polyatomic ion, follow the same rules but treat the polyatomic ion as a single unit.

Writing Formulas w/Polyatomic Ions a group of atoms that stay together and have a single, overall charge. Ba2+ and SO42– BaSO4 barium sulfate Mg2+ and NO21– Mg(NO2)2 magnesium nitrite NH41+ and ClO31– NH4ClO3 ammonium chlorate Sn4+ and SO42– Sn(SO4)2 tin (IV) sulfate ? Fe3+ and Cr2O72– Fe2(Cr2O7)3 iron (III) dichromate NH41+ and N3– (NH4)3N ammonium nitride

Rules for Parentheses There is a (polyatomic ion) present and… Parentheses are used only when the following two condition are met: There is a (polyatomic ion) present and… There are two or more of that in the formula. Examples: NaNO3 NO31- , but there is only one of it. Co(NO3)2 NO31- there are two of them (NH4)2SO4 NH41+ there are two of them; SO42- there is only one of it. Co(OH)2 OH1- there are two of it. Al2(CO3)3 CO32- there are three of them. NaOH OH1- there is only one of it.

Pattern to Memorizing Nomenclature XY “-ide” XYO4 XYO3 XYO2 XYO “per___-ate” “-ate” “-ite” “hypo___-ite” 1 more oxygen normal 1 less oxygen 2 less oxygen

Physical Characteristics Physical characteristics result from the strong attractive forces between charged particles and the crystal structure High melting and boiling points Lots of energy necessary to break strong bonds Solid at room temperature Stable crystal structure Hard and brittle Crystal allows compound to withstand great force Too much force causes repulsive forces to overpower attractive forces and the crystal shatters Conduct electricity when melted and dissolved in water Charged particles that are able to move