Naming and Formulas. Molecular Compounds. Molecular Compounds. Molecular Compounds

Transcription

1 Acidic Compounds Naming and Formulas Molecular compounds are made of nonmetals only (includes flagpole elements!) Electrons are shared (molecular), not transferred (ionic) No transfer = no charge = no ions! Prefixes are used during naming Molecular is the same thing as covalent Prefixes used (memorize these!!!): Steps to find the chemical name: 1 atom hexa- mono- 6 atoms 1) Name the first element 2 atoms 3 atoms 4 atoms 5 atoms heptaoctanonadeca- ditritetrapenta- 7 atoms 8 atoms 9 atoms 10 atoms 2) Add a prefix to the first element (do not use mono- for the 1 st element!) 3) Name the second element, changing the ending to ide 4) Add a prefix to the second element 1

2 What to do if a molecular compound ends with element S, P, N or O: a) sulphur becomes sulphide b) phosphorus becomes phosphide c) nitrogen becomes nitride d) oxygen becomes oxide ex. N 2 O: ex. CO 2 : ex. P 4 O 10 : dinitrogen carbon monoxide dioxide tetraphosphorus decoxide Steps to find the chemical formula: 1) Write the symbol for the first element, but DO NOT USE CHARGE! 2) Convert the first prefix into a subscript 3) Write the symbol for the second element, but DO NOT USE CHARGE! 4) Convert the second prefix into a subscript ex. carbon monoxide: CO(g) ex. carbon tetrachloride: CClCl 4 (l) ex. sulphur dioxide: SO 2 (g) 2

3 Metals in their pure form exist as single atoms, referred to as monatomic (ex. Cu) Noble gases are also monatomic (ex. He) Pure non-metal elements that don t exist as single atoms are called polyatomic and contain molecular bonds (ex. S 8 ) Pure elements made of two atoms are also specifically called diatomic (ex. Cl 2 ) Polyatomic pure elements: N 2, O 2, F 2, P 4, S 8, Cl 2, Br 2, I 2, At 2 and H 2 They form a flagpole shape! (MEMORIZE) Note: N 2, O 2, F 2, Cl 2, Br 2, I 2, At 2 and H 2 are the only ones that are diatomic Compounds in chemical reactions have states to help us identify them Use the periodic table to determine the states of pure elements, either (s), (l) or (g) Molecular compounds are either (s), (l) or (g), depending on the exact formula For sure: compounds of N x O y, C x O y and S x O y are gases!! Ionic compounds contains a metal ion or a polyatomic ion (or both) Metals are either monovalent or multivalent Monovalent: one charge, ex. K +, Be 2+ Multivalent: multiple charges possible, ex. Fe 2+ /Fe 3+, Cu + /Cu 2+ (but only one at a time!) Use Roman numerals with multivalent metals 3

4 Steps to find the chemical name: 1) Write the name of the first ion 2) Write Roman numerals for charge, if it is a multivalent metal 3) Write the name of the second ion 4) Change the ending to -ide if the second ion is a non-metal (if polyatomic, do not change its ending!) What to do if an ionic compound ends with element S 2-, P 3-, N 3- or O 2- : a) sulphur becomes sulphide b) phosphorus becomes phosphide c) nitrogen becomes nitride d) oxygen becomes oxide Some ionic compound names end with the term hydrate (seen as H 2 O in a formula) For these compounds, prefixes are needed to indicate how many waters are attached: 1 atom 2 atoms 3 atoms 4 atoms 5 atoms hexa- mono- 6 atoms 7 atoms 8 atoms 9 atoms 10 atoms hepta- di- octa- tri- nona- tetra- deca- penta- Tips on hydrate compounds: a) state is always solid (s) b) waters are included in the molar mass of the entire compound 4

5 ex. AlCl 3 : aluminum chloride ex. FeSO 4 : iron (II) sulphate ex. CuSO 4 5H 2 O: copper (II) sulphate pentahydrate Steps to write the chemical formula: 1) Write the symbol of the first ion 2) Write the symbol of the second ion 3) Cross-multiply charges; place subscripts to the bottom right of element symbols 4) Drop the charges, and reduce subscripts! 5) Write the state for the compound ex. sodium chloride: Two terms to remember: ( Na + ) 1 ( Cl - ) 1 ex. tin (II) fluoride: ( Sn 2+ ) 1 ( F - ) 2 ex. tin (IV) oxide: ( Sn 4+ ) 2 ( O 2- ) 4 NaCl(s) SnF 2 (s) SnO 2 (s) cation ion with positive (+) charge TIP: look for the + in the middle of cation anion ion with negative (-) charge TIP: a negative ion 5

6 The back of your periodic table has a solubility chart on it (upper right): a) 1 st row of the chart lists common anions b) 2 nd row ( very soluble ) lists cations expected to not form precipitates (dissolve) when in solution with those anions (aq) c) 3 rd row ( slightly soluble ) lists cations expected to form precipitates (solids) when in solution with those anions (s) If you are asked to identify whether a compound dissolves or forms a precipitate: 1) Find the anion in the top row 2) Look directly below the anion to find the cation that is also part of the compound 3) If the cation shows up in the 2 nd row (very soluble), it dissolves easily (aq) 4) If the cation shows up in the 3 rd row (slightly soluble), it will precipitate (s) ex. Will CuCO 3 (s) dissolve in water? No ex. A powder made of NaCH 3 COO (s), Pb(NO 3 ) 2 (s) and KI (s) is mixed with water. What precipitate is expected to form? PbI 2 (s) If an ionic compound is dry, it is in the solid (s) state If the compound is molten (melted), the state is liquid (l) If water is present, use the solubility chart: aqueous (aq) if it is very soluble solid (s) if it is slightly soluble 6

7 Acidic Compounds An acid is formed when a specific compound combines with water The original compound could be (s), (l) or (g) Once dissolved, the acid always has a state of aqueous, (aq) ex. hydrogen iodide, HI(s), dissolves in water to form hydroiodic acid, HI(aq) Acidic Compounds An acid contains H + and a non-metal ion or polyatomic ion Naming rules (see back of periodic table): 1) hydrogen ide becomes hydro ic acid 2) hydrogen ate becomes ic acid 3) hydrogen ite becomes ous acid Use the tip sheet for a strategy to use these! Acidic Compounds examples: HI(aq) hydrogen iodide hydroiodic acid H 3 PO 4 (aq) hydrogen phosphate phosphoric acid HNO 2 (aq) hydrogen nitrite nitrous acid sulphuric acid hydrogen sulphate H 2 SO 4 (aq) sulphurous acid hydrogen sulphite H 2 SO 3 (aq) benzoic acid hydrogen benzoate HC 6 H 5 COO(aq) hydrobromic acid hydrogen bromide HBr(aq) 7