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Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like to Gain 4 electrons N would like to Gain 3 electrons O would like to Gain 2 electrons Electron Dot Structures Symbols of atoms with dots to represent the valence-shell electrons 1 2 13 14 15 16 17 H 18 He: Li Be B C Na Mg Al N O Si P S : F :Ne : :Cl :Ar : Chemical bond • A chemical bond forms when outer-shell electrons of different atoms come close enough to each other to interact and rearrange themselves into a more stable arrangement. Types of Chemical Bonds • Ionic bonds formed when metal atoms combined with non-metal atoms • Metallic bonds formed when metal atoms combined with metal atoms. • Covalent bonds formed when non-metal atoms combined with non-metal atoms. Ionic Compounds 1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions. The coordination number of an ionic lattice is written as a ratio x:y How many chlorine ions surround each sodium ion and vice versa? NaCl coordination number- 6:6 Hardness and Brittleness Figure 6.4 The repulsion between like charges causes this sodium chloride crystal to shatter when it is hit sharply. Electrical Conductivity • In the solid form, ions in sodium chloride are held in the crystal lattice and are not free to move so cannot conduct electricity. • When the solid melts the ions are free to move. • In a similar way, when sodium chloride dissolves in water, the ions separate and are free to move towards the opposite charge. Properties of Ionic Compounds – Forms crystal composed of 3d array of ions (ionic network lattice) – Have high melting and boiling temperatures. – Are hard but brittle – Do NOT conduct electricity in the solid state – They will only conduct electricity if they are melted or dissolved in water. Structure • From the properties we can conclude: – The forces between the particles are strong. – There are no free-moving electrons present, unlike in metals. – There are charged particles present, but in solid state they are not free to move. – When an ionic compound melts, however, the particles are free to move and the compound will conduct electricity. Use Electron shell diagram and simple equation to show the formation of: • NaCl • MgO Naming Binary Ionic Compounds Contain 2 different elements Name the metal first, then the nonmetal as -ide. NaCl ZnI2 Al2O3 Examples: sodium chloride zinc iodide aluminum oxide Practise Complete the names of the following binary compounds: Na3N ________________ KBr ________________ Al2O3 ________________ MgS _________________________ Solution Complete the names of the following binary compounds: Na3N sodium nitride KBr potassium bromide Al2O3 aluminum oxide MgS magnesium sulfide Transition Metals Many form 2 or more positive ions 1+ 2+ 1+ or 2+ 2+ or 3+ Ag+ Cd2+ Cu+, Cu2+ Fe2+, Fe3+ silver ion cadmium ion Zn2+ zinc ion copper(I) ion iron(II) ion copper (II) ion iron(III) ion Write symbols for these: • Potassium ion • Magnesium ion • Copper (II) ion • Chromium (VI) ion • Barium ion • Mercury (II) ion Formula of ionic compounds Criss-Cross Method 1. Write the symbols for the ions side by side. Write the cation first. • Al3+ O22. Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion. • Al2 O3 3. Check the subscripts and divide them by their largest common factor to give the smallest possible whole-number ratio of ions. Then write the formula. • Al2O3 • For Al: 2 x 3+ = 6+ For O: 3 x 2- = 6- Criss-Cross Method Example 1: Calcium and Oxygen Calcium Ca2+ Oxide O2- Ca2+ O2Ca2O2 CaO Criss-Cross Method Example 2: Magnesium and Phosphorus Magnesium Mg2+ Phosphorus P3- Mg2+ P3- Mg3P2 The sum of the cation charge and the sum of the anion charge must cancel each other so that the compound formed is neutral. Practise 1. The formula for the ionic compound of Na+ and O2- is 1) NaO 2) Na2O 3) NaO2 2. The formula of a compound of aluminum and chlorine is 1) Al3Cl 2) AlCl2 3) AlCl3 3. The formula of Fe3+ and O2- is 1) Fe3O2 2) FeO3 3) Fe2O3 Solution A. The formula for the ionic compound of Na+ and O2- is 2) Na2O B. The formula of a compound of aluminum and chlorine is 3) AlCl3 C. The formula of Fe3+ and O2- is 3) Fe2O3 Sample Problem 7-1 •Write the formulas for the binary ionic compounds formed between the following elements: A. lithium and fluorine B. lithium and oxygen Names of Variable Ions Use a roman number after the name of a metal that forms two or more ions Transition metals and the metals in groups 4A and 5A FeCl3 (Fe3+) iron (III) chloride CuCl SnF4 PbCl2 Fe2S3 (Cu+ ) (Sn4+) (Pb2+) (Fe3+) copper (I) chloride tin (IV) fluoride lead (II) chloride iron (III) sulfide II. Stock system (roman numerals) Example: Fe2+ Fe3+ • Iron(II) • Iron(III) CuCl • copper(I) chloride CuCl2 • copper(II) chloride Sample Problem 7-2 a. Write the formula and give the name for the compound formed from the ions Cr3+ and F-. b. Write the name for Cu3N2. Here are the changes in the electronic structure of iron to make the 2+ or the 3+ ion. Fe [Ar] 3d64s2 Fe2+ [Ar] 3d6 Fe3+ [Ar] 3d5 Learning Check Complete the names of the following binary compounds with variable metal ions: FeBr2 iron (_____) bromide Cu2O copper (_____) oxide SnCl4 ___(_____ ) ______________ Fe2O3 ________________________ CuS ________________________ Solution Complete the names of the following binary compounds with variable metal ions: FeBr2 iron ( II ) bromide Cu2O copper ( I ) oxide SnCl4 tin (IV) chloride Fe2O3 iron (III) oxide CuS copper (II) sulfide Learning Check Name the following compounds: A. CaO 1) calcium oxide 2) calcium(I) oxide 3) calcium (II) oxide B. SnCl4 1) tin tetrachloride 3) tin(IV) chloride C. Co2O3 1) cobalt oxide 3) cobalt trioxide 2) tin(II) chloride 2) cobalt (III) oxide Solution Name the following compounds: A. CaO 1) calcium oxide B. SnCl4 3) tin(IV) chloride C. Co2O3 2) cobalt (III) oxide Learning Check Write the correct formula for the compounds containing the following ions: A. Na+, S21) NaS 2) Na2S 3) NaS2 B. Al3+, Cl1) AlCl3 2) AlCl 3) Al3Cl C. Mg2+, N31) MgN 2) Mg2N3 3) Mg3N2 Solution A. Na+, S22) Na2S B. Al3+, Cl1) AlCl3 C. Mg2+, N33) Mg3N2 Practise Name the following ionic compounds: Na2O K2S CaCl2 AgCl MgBr2 AlN Ba3As2 AlH3 ZnI2 Li3P Nomenclature of binary ionic compounds Answers: Na2O = sodium oxide K2S = potassium sulfide MgBr2 = magnesium bromide AlN = aluminum nitride Ba3As2 = barium arsenide CaCl2 = AgCl = silver chloride AlH3 = aluminum hydride ZnI2 = zinc iodide phosphide calcium chloride Li3P = lithium III. Polyatomic Ions A charged group of covalently bonded atoms Combine with ions of opposite charge to form ionic compounds Ex: NH4+, NO3-, SO42- Nomenclature of binary ionic compounds Some polyatomic anions that you must know: NO3- = nitrate NO2- = nitrite SO4 2 - = sulfate SO32- = sulfite PO43- = phosphate PO33- = phosphite CO32- = carbonate HCO31- = hydrogen carbonate or bicarbonate OH- = hydroxide CN- = cyanide C2H3O2- = acetate C2O42- = oxalate III. Polyatomic Ions Most common ion is given the ending –ate. • One less oxygen than –ate ends in –ite. • One less oxygen than –ite is given the prefix hypo. • One more oxygen than -ate is given the prefix per. ClO4 • perchlorate ClO3 • chlorate NO3 • nitrate ClO2 • chlorite NO2 • nitrite ClO • hypochlorite Sample Problem 7-3 a. Write the formula for potassium sulfate. b. Write the formula for calcium carbonate. c. Write the formula for tin(IV) sulfate. Ionic Nomenclature Practice potassium chloride K+ Clmagnesium nitrate KCl Mg2+ NO3 copper(II) chloride Mg(NO3)2 Cu2+ Cl- CuCl2 Nomenclature of binary ionic compounds Naming salts composed of the polyatomic ions is the same as with the monatomic anions. Metal name then polyatomic name. NaOH sodium hydroxide H2SO4 hydrogen sulfate Ba(NO3)2 barium nitrate CsNO2 cesium nitrite Sometimes there is a common name: KHCO3 potassium hydrogen carbonate or potassium bicarbonate Note: the polyatomic anions must be memorized. Name the following ionic compounds: NaHCO3 K2SO3 MgSO4 Ca(OH)2 NH4NO3 Zn(NO3)2 KCN Li3PO4 H2PO4 HNO3