Presentation on theme: "Ions Atoms of an element with different numbers of electrons are called ions: –ions with more electrons than the atom are negatively charged and called."— Presentation transcript:
Ions Atoms of an element with different numbers of electrons are called ions: –ions with more electrons than the atom are negatively charged and called anions (pronounced AN-eye-un). –ions with fewer electrons than the atom are positively charged and called cations (pronounced CAT-eye-un).
Ionic Compounds Bonds occur between atoms as a result of interactions among the valence electrons. When the interaction is to strip electrons, the bond is said to be ionic and the entity formed is an ionic compound. How do I recognize an ionic compound? Compounds between metals and nonmetals tend to be ionic. (Nonmetals strip electrons from metals to form the anions.) NaCl formula unit AND empirical formula This is a crystal of NaCl. Na + Cl -
Ionic Compounds Ionic compounds are made of cations and anions, held together by electrostatic attraction: –opposite electrical charges attract each other (like electrical charges repel each other) Ionic compounds do not exist as discrete molecules, but as structured aggregates (crystals). –In NaCl, an ionic compound, Na exists as Na + and Cl exists as Cl -. The overall charge of an ionic compound is ZERO!
Ionic Charges – Monatomic Ions Metal ions typically have a positive charge. –Group 1A metals always have a +1 charge: Li +, Na +, K +, etc. (H is mostly H + but can form H - ) –Group 2A metals always have a +2 charge: Mg 2+, Ca 2+, Ba 2+, etc. –Some metal ions (usually transition metals) can have more than one charge: Fe 2+, Fe 3+, Cu 2+, Cu + Nonmetal ions typically have a negative charge. –Group 7A nonmetals typically have a -1 charge: F -, Cl -, Br -, etc. –Group 6A metals typically have a -2 charge: O 2-, S 2-, Se 2-, etc. !!! Knowing what the Groups mean and knowing where the metal/nonmetal boundary is on the periodic table is a BIG help when dealing with ions and ionic compounds !!!
A group of atoms that is covalently bonded yet still has a charge is a polyatomic ion. –NO 3 - –SO 4 2- –PO 4 3- –ClO 2 - –etc. Polyatomic Ions phosphate ion, PO 4 3-
Naming Ionic Compounds 1.Name the cation (metal or NH 4 + ). 2.Name the anion (nonmetal or polyatomic anion). Name monatomic (nonmetal) anions by replacing the end of the nonmetal with –ide. oxygen becomes oxide fluorine becomes fluoride sulfur becomes sulfide Memorize the names of the polyatomic anions. NaCl NH 4 I Ba 3 P 2 KCN sodium chloride ammonium iodide barium phosphide potassium cyanide
Naming Metal Ions When More Than One Ion is Possible Two methods Stock system (Roman numeral shows the charge of the cation) –Fe 2+ is iron(II) –Fe 3+ is iron(III) –Sn 2+ is tin(II) –Sn 4+ is tin(IV) Classic (-ic, -ous) system –-ic is for the ion with the higher charge –-ous is for the ion with the lower charge –Fe 2+ is ferrous –Fe 3+ is ferric –Sn 2+ is stannous –Sn 4+ is stannic
Naming Polyatomic Ions and Polyatomic Oxyanions Polyatomic ions – memorize them! (examples are CN -, NH 4 +, OH -, O 2 2-, SCN -, SO 4 2-, SO 3 2- ) Polyatomic oxyanions* are methodically named: ▫sulfate: SO 4 2- (higher oxidation number) ▫sulfite: SO 3 2- (lower oxidation number) ▫perchlorate: ClO 4 - ▫chlorate: ClO 3 - ▫chlorite: ClO 2 - ▫hypochlorite: ClO - *You must memorize these, too!
Naming Ionic Compounds - Examples MgCl 2 CuCO 3 CuNO 3 KIO 4 (NH 4 ) 3 PO 4
Naming Ionic Compounds - Examples MgCl 2 CuCO 3 CuNO 3 KIO 4 (NH 4 ) 3 PO 4 magnesium chloride copper(II) carbonate or cupric carbonate copper(I) nitrate or cuprous nitrate potassium periodate ammonium phosphate
Writing Formulas for Ionic Compounds The overall ionic compound MUST BE ELECTRICALLY NEUTRAL. KF MgO (NH 4 ) 2 S Ti 3 N 2 Pb 3 (PO 4 ) 4 Al(OH) 3 potassium fluoride magnesium oxide ammonium sulfide titanium(II) nitride lead(IV) phosphate aluminum hydroxide One way to determine the formula for the compound formed between Ca and P is to make the charge of the cation the subscript of the anion, and vice versa (like a swap)*: P 3- Ca 3 P 2 2+ Ca *Before doing the swap, check the charges on the ions. If they are equal and opposite, just write the two element symbols, cation first (example is MgO). If the charges are NOT equal and opposite, then it is okay to do the “swap.”
Naming Hydrates Hydrates are ionic compounds with a specific number of water molecules attached. Name the ionic compound, use the Greek prefix to indicate the number of waters of hydration, and end with the word “hydrate.” CuSO 45H 2 O copper(II) sulfate pentahydrate BaCl 2 2H 2 O barium chloride dihydrate
Naming Binary Molecular Compounds 1.Name the element farthest to the left on the periodic table. (Exception: O is written last unless it’s bonded to F.) 2.If both elements are in the same group, name the lower one first. 3.Give the ion name of the second element (-ide ending). 4.Greek prefixes give the number of each atom in the formula. mono-1 di-2 tri-3 tetra-4 penta-5 hexa-6 hepta-7 octa-8 nona-9 deca-10 COcarbon monoxide CO 2 carbon dioxide P 4 O 10 tetraphosphorus decaoxide N2ON2Odinitrogen monoxide
Naming Acids… with an anion name that ends in –ide NOT IN SOLUTION, the name of the acid is just the name of the binary molecular compound: –HCl(g) is hydrogen chloride IN SOLUTION, –replace hydrogen with hydro- –change –ide to –ic –add the word “acid” –HCl(aq) is hydrochloric acid
Naming Oxoacids (Acids with an anion that contains oxygen and has a name that ends in –ate or -ite) Modify the oxyanion name: -ate anion becomes –ic –nitrate becomes nitric -ite anion becomes –ous –nitrite becomes nitrous sulfuric acid sulfurous acid sulfate: SO 4 2- H 2 SO 4 sulfite: SO 3 2- H 2 SO 3 perchlorate: ClO 4 - HClO 4 chlorate: ClO 3 - HClO 3 chlorite: ClO 2 - HClO 2 hypochlorite: ClO - HClO perchloric acid chloric acid chlorous acid hypochlorous acid
Naming Acid Salts An acid salt is a polyprotic acid (an acid with more than one H) that has been only partially neutralized. –if H 2 X is the acid, the acid salt is MHX, where M is a cation. NaHSO 4 is an acid salt. –sodium hydrogen sulfate –sodium bisulfate –if H 3 X is the acid, the acid salts are MHX and MH 2 X. Na 2 HPO 4 is an acid salt. –sodium hydrogen phosphate NaH 2 PO 4 is also an acid salt –sodium dihydrogen phosphate
Names of Common Chemicals See separate powerpoint file.
Names of Common Chemicals You are also responsible for knowing the names and formulas of all chemicals you encounter in your laboratory experiments.