Section 2.6: Molecular and Ionic Compounds By Doba Jackson, Ph.D.

Molecules, Ions, and Chemical Bonds Covalent Bond: A bond that results from the sharing of electrons between atoms. Ionic Bond: A bond that results from oppositely charged ions that are electrostaticlly attracted to each other.

Definitions of Molecules, Ions, and Chemical Bonds Ionic Bond: An electrostatic attraction between charged particles. Typically a metal bonded to a nonmetal. Ion: A charged atom or molecule. Cation: A positively charged particle. Most cations are metals. Anion: A negatively charged particle. Nonmetals tend to form anions.

Ions, and Chemical Bonds In the formation of sodium chloride, one electron is transferred from the sodium atom to a chlorine atom. Na +1 + Cl -1 Na + Cl 2 11 protons 10 electrons 17 protons 18 electrons 11 protons 11 electrons 17 protons 17 electrons 1 2

Evidence for existence of ions

We can predict many element’s ionic charge based on its location on the periodic table

Naming Ionic Compounds Naming (IUPAC) Cation Anion Na +1 Cl -1 Sodium Chloride Metals tend to form Cations Nonmetals tend to form Anions

Naming Ionic Compounds Ionic Compound: A neutral compound in which the total number of positive charges must equal the total number of negative charges. Some binary Ionic Compounds Cation – Anion(ide) CationAnion Ionic Compound cation anion(ide) C +x A -y CyAxCyAx aluminum sulfide:Al 2 S 3 Al +3 S -2 sodium chlorideNaClNa +1 Cl -1 magnesium oxideMgOMg +2 O -2

Determine the charge on each ionic compound and name the compound MgS BaF 2 AlP Ga 2 O 3 Li 2 O Mg 3 N 2 CaS Fe +3 O -2 Pb +4 O -2 Ni +2 Br -1 Manganese (IV) Oxide Tungsten (VI) bromide Mg +2 Ba +2 Al +3 Ga +3 Li +1 Mg +2 Ca +2 Mn +4 W +6 S -2 F -1 P -3 O -2 N -3 S -2 O -2 Br -1 Magnesium sulfide Barium flouride Aluminum Phosphide Gallium oxide Lithium oxide Magnesium nitride Calcium sulfide Iron (III) oxide Lead (IV) oxide Nickel Bromide Fe 2 O 3 PbO 2 NiBr 2 MnO 2 WBr 6

Some transition metals have more than one stable charge

What happens when the cation has more than one oxidation state Some binary Ionic Compounds Cation Anion(ide) CationAnion Ionic Compound cation (x) anion(ide) C +x A -y CyAxCyAx lead (II) flouridePbF 2 Pb +2 F -1 iron (III) oxideFe 2 O 3 Fe +3 O -2 tin (II) chlorideSnCl 2 Sn +2 Cl -1 Use Roman numerals in parentheses to indicate the charge on metals that form more than one kind of cation.

Molecules, Ions, and Chemical Bonds Covalent Bond: A bond that results from the sharing of electrons between atoms. Ionic Bond: A bond that results from oppositely charged ions that are electrostaticlly attracted to each other.

Definitions of Ionic and Covalent compounds Ionic bonds are a result of a combination of a metal (electropositive element) and a non- metal (electronegative element). In ionic bonds, atoms are attracted to each other by opposite charges. Covalent bonds are a result of the combination of two non-metals (two electronegative elements). In covalent bonds, atoms are attracted to each other by a shared pair of electrons.

A Comparison of Ionic and Covalent Bonds

Points to consider: Ionic verses Covalent compounds Point 1: Ionic compounds are usually solids (when pure) Point 2: Ionic compounds have very high boiling and melting points Point 3: Covalent compounds can be either solids, liquids or gases Point 4: Covalent compounds have relatively lower boiling and melting points

Why does NaCl have such high boiling and melting points?

A chemical representation of a covalent compound (ethanol)

Predict whether each compound is an ionic or molecular compound. KI, component in table salt H 2 O 2, antioxidant CHCl 3, anesthetic Li 2 CO 3, antidepressants Ionic: 1 metal 1 nonmetal Molecular: 2 nonmetals Molecular: 3 nonmetals Ionic: 1 metal 2 nonmetals

To name nonmetals, we first have to understand a concept called Electronegativity Electronegativity: The ability of an atom in a molecule to attract the shared electrons in a covalent bond.

Naming Covalent Compounds: Must know these prefixes

Choose which compound is more electronegative, then change the suffix to -ide - Write the name: electropositive - electronegative - Add the suffix “ide” to the end of the electronegative atom. - Use the prefixes to indicate the multiplicity of the both atoms.

Example: naming N 2 O 4 N2O4N2O4 The second element (Oxygen) is more electronegative and takes the name of the element with an “ide” modification to the ending. The first element (Nitrogen) is more electropositive and takes the name of the element. The prefix is added to the front of each to indicate the number of each atom. dinitrogen tetraoxide

WORKED EXAMPLE Give systematic names for the following compounds Solution (a)PCl 3 (b) N 2 O 3 (c) P 4 O 7 (d) BrF 3 Phosphorus trichloride Dinitrogen trioxide Tetraphosphorus heptoxide Bromine trifluoride