Compounds A compound is a pure substance that contains two or more elements that are chemically bonded to each other Compounds form when the electrons of two or more elements interact and are composed of either: Molecules Ions

Molecules Molecule: A group of atoms combined in definite proportions and held together by strong attractive forces called covalent chemical bonds Covalent bonds are formed when atoms share two or more electrons. The smallest representative particle of a molecular compound

Molecular Compounds Molecular compounds composed of molecules that contain more than one type of atom Most molecular substances are composed of non-metals only. Examples: Water (H 2 O) Ethyl alcohol (C 2 H 6 O) Carbon dioxide (CO 2 ) Ammonia (NH 3 )

Ionic Compounds Ionic compounds are composed of ions (both cations and anions) and usually contain a metal and one or more nonmetals. “Salt” (NaCl) Contains Na + and Cl - ions Tums (CaCO 3 ) Contains Ca 2+ and CO 3 2- ions Milk of Magnesia [Mg(OH) 2 ] Contains Mg 2+ and OH -

Ionic Compounds Ionic compounds such as NaCl are formed when one or more electrons are transferred from one atom to another the resulting cation and anion are strongly attracted to each other and are held together by an ionic bond resulting from electrostatic forces of attraction

Chemical Formulas The composition of a compound is generally shown using a chemical formula: A shorthand notation that describes the types and relative (or exact) numbers of each atom (or ion) present in a pure substance Chemical formulas always contain: Elemental symbols Subscripts Show the relative (or exact) number of each type of atom or ion

Chemical Formulas Molecular Formula chemical formula that tells the actual number of each type of atom in a molecule Empirical Formula chemical formula that tells the smallest whole number ratio of each type of atom in a molecule Acetic AcidC 2 H 4 O 2 CH 2 O Ascorbic AcidC 6 H 8 O 6 C 3 H 4 O 3 Sodium SulfateNa 2 SO 4

Ionic Compounds The ions present in an ionic compound can be either: Monoatomic Polyatomic Monoatomic ion: a charged species containing a single atom that has gained or lost electrons Al 3+ S 2-

Predicting Ion Charge – Monoatomic Ions Many atoms gain or lose electrons in such a way that they end up with the same number of electrons as the nearest (closest in atomic number) noble gas. “octet” rule Ca (20p, 20e - )  Ca 2+ (20p, 18e - ) [Ar: 18p,18e - ] O (8p, 8e - )  O 2- (8p, 10e - ) [Ne: 10p, 10e - ]

Predicting Ion Charge – Monoatomic Ions Using the octet rule you can easily determine the charge on most of the monoatomic ions formed by the main group elements. Main group metal cations: Charge = group number Main group nonmetal anions: Charge = group # - 8 (or simply count the number of “spaces” away from the nearest noble gas and add a negative sign)

Common Monoatomic Ions In general: Metal atoms and hydrogen lose e- and form cations. Nonmetal atoms gain e- and form anions. Know These! Zn 2+ Ag + P 3-

Common Monoatomic Ions Many transition metals and a few main group elements form more than one ion. Main group Fe 2+ Fe 3+ Cu + Cu 2+ Mn 2+ Mn 3+ Co 2+ Co 3+ Bi 3+ Bi 5+ Cr 2+ Cr 3+ Sn 2+ Sn 4+ Pb 2+ Pb 4+ Main group

Names of Monoatomic Ions - Cations Cations formed by a metal have the same name as the metal. K + potassium ion Ca 2+ calcium ion Al 3+ aluminum ion If a metal forms more than one cation, use Roman numerals in ( ) after the name of the metal to show its charge. Fe 2+ iron (II) ion Fe 3+ iron (III) ion Cu + copper (I) ion Cu 2+ copper (II) ion

Names of Monoatomic Ions - Anions Monoatomic anions are named by: dropping the ending of the element’s name adding “ide” NnitrogenOoxygen N 3 - O 2 - nitrideoxide

Polyatomic Ions Polyatomic ion: an electrically charged group of two or more atoms that are held together by covalent bonds Polyatomic ions cannot be broken into smaller pieces. Examples: NO 3 - SO 4 2- HCO 3 - PO 4 3-

Polyatomic Ions You are responsible for knowing the names and formulas of all ions listed in your syllabus, including the common polyatomic ions: AmmoniumNH 4 + HydroxideOH - CyanideCN - NitrateNO 3 - AcetateC 2 H 3 O 2 - SulfateSO 4 2- Bisulfate (Hydrogen sulfate)HSO 4 - CarbonateCO 3 2- Bicarbonate (Hydrogen carbonate) HCO 3 - PhosphatePO 4 3-

Naming Oxyanions Many of the polyatomic anions are oxyanions. polyatomic anions containing one or more oxygens attached to a central atom To name an oxyanion, drop the ending of the central atom name and add: “ate”most common oxyanion of the element “ite”1 less oxygen NO 3 - nitrateSO 4 2- sulfate NO 2 - nitriteSO 3 2- sulfite CO 3 2- carbonatePO 4 3- phosphate PO 3 3- phosphite

Oxyanions Noble gases 3A4A5A6A7A “ate” oxyanions to memorize

Oxyanions The halogens typically form 4 different oxyanions: “per”1 more O than the “ate” oxyanion “hypo”1 less O than the “ite” oxyanion ClO 4 - perchloratemost oxygens ClO 3 - chloratemost common ClO 2 - chlorite1 less O ClO - hypochloritefewest oxygens

Oxyanions Anions derived by adding one or two H + to an oxyanion: add “hydrogen” or “dihydrogen” as prefix to oxyanion name CO 3 2- carbonate HCO 3 - hydrogen carbonate (usually called bicarbonate) PO 4 3- phosphate H 2 PO 4 - dihydrogen phosphate

Writing Formulas for Ionic Compounds Ionic compounds are always represented using an empirical formula with the cation shown first. The formula for an ionic compound must be electrically neutral. Total positive charge = total negative charge Although ions are present in an ionic compound, the formula does NOT explicitly show the charge of the ions.

Writing Formulas for Ionic Compounds Ionic compounds must be electrically neutral. Total positive charge = total negative charge Na + + Cl - NaCl (1 pos, 1 neg) + Na + Cl -

Writing Formulas for Ionic Compounds Ca 2+ + Cl - CaCl (2 pos, 1 neg) Ca 2+ Cl - Ca Cl - CaCl 2 (2 pos, 2 neg) Ca 2+ Cl -

Writing Formulas for Ionic Compounds To write the empirical formula of an ionic compound from its name: 1. Identify the formula including charge for each ion. 2. Combine the ions in a ratio that gives an electrically neutral compound.

Writing Formulas for Ionic Compounds If charges on the ions are equal in magnitude (but opposite in sign), then combine the ions in a 1:1 ratio. Ca 2+ SO 4 2- HCO 3 - Na +

Writing Formulas for Ionic Compounds If charges on the ions are different, then flip-flop the charges (i.e. the charge of one ion becomes the subscript of the other ion). Place ( ) around a polyatomic ion IF more than one is needed.

Writing Formulas for Ionic Compounds Example: Write the correct formula for the following ionic compounds. Zinc bromide Aluminum carbonate Iron (II) phosphate Tin (IV) sulfate Magnesium hydroxide

Writing Formulas for Ionic Compounds Example: Write the correct formula for the following ionic compounds. Sodium bicarbonate Ammonium sulfate Potassium phosphite Sodium hypochlorite Copper (I) oxide

Writing Formulas for Ionic Compounds Remember: Use empirical formulas Formulas must be electrically neutral Do not show the charges of each ion in the final formula that you write Use parentheses around polyatomic ions if more than one is present in the formula Do not use ( ) around monoatomic ions Do not use ( ) around a single polyatomic ion

Naming Ionic Compounds Ionic compounds are named using the cation name followed by the anion name CaBr 2 calcium bromide NaClOsodium hypochlorite Mg 3 (PO 4 ) 2 magnesium phosphate If the cation can form ions with more than one charge, you must specify the charge: Fe 2 S 3 iron (III) sulfide PbO 2 lead (IV) oxide

Naming Ionic Compounds Example: Name the following ionic compounds. Na 2 SO 4 FeCl 3 (NH 4 ) 3 PO 4 KClO 4 Cu 2 CO 3 Sn(SO 4 ) 2

Common “Household” Chemicals You are responsible for knowing the names and formulas for the chemical present in: Baking soda sodium bicarbonate NaHCO 3 Table salt Sodium chloride NaCl Bleach Sodium hypochlorite NaClO or NaOCl