The following pages provide the answers to the IONIC COMPOUNDS AND IONIC BONDS PAPER LAB.

Transcription

1 The following pages provide the answers to the IONIC COMPOUNDS AND IONIC BONDS PAPER LAB. However, I did not draw the models. If you don t understand how I got the formulae, please see me in class.

2 IONIC BONDS AND IONIC COMPOUNDS Name: 1. Define the following terms: a) ion: a charged particle, due to imbalance between total protons and electrons b) ionic bond: the strong electro-magnetic attraction between oppositely charged ions c) ionic compound: a salt; a compound comprised of positive and negative ions in an arrangement called the crystal lattice d) cation: a positively charged ion, due to loss of electrons e) anion: a negatively charged ion, due to gain of electrons f) monoatomic ion: the ion of a single atom; metals are generally cations, and non-metals anions. g) polyatomic ion: two or more atoms covalently bonded acting as a single charged particle. 2. In the table below, write the symbols for each ion with its correct charge: aluminum Al 3+ chloride Cl - magnesium Mg 2+ potassium K + barium Ba 2+ fluoride F - nitride N 3- sodium Na + bromide Br - iodide I - oxide O 2- strontium Sr 2+ calcium Ca 2+ lithium Li + phosphide P 3- sulfide S 2-3. What is the difference between fluorine and fluoride? _Fluorine is the neutral atom; fluoride is the negative ion. All non-metals change their ending to ide when bonded or as anions. 4. If you were asked to write the chemical formula for sodium chloride, you would write NaCl. No Problem! However, if you had to write the formula for iron chloride, you would be unsure about the correct formula. Why would there be any confusion or uncertainty about the correct formula for iron chloride? There would be confusion because iron is a multi-valent metal. Most of the transition block and the large p-block metals can achieve a variety of more stable electron configurations by losing a variety of electrons, hence these metals can have a variety of positive ionic charges.

3 5. Under what circumstances should you add a Roman numeral to the name of a cation? A Roman numeral is added to indicate the charge of a multi-valent metal. 6. In the table below write the symbol for each cation with its correct charge: iron (II) Fe 2+ cobalt (II) Co 2+ scandium (III) Sc 3+ tin (IV) Sn 4+ iron (III) Fe 3+ cobalt (III) Co 3+ titanium (II) Ti 2+ manganese (IV) Mn 4+ copper (I) Cu + nickel (II) Ni 2+ titanium (IV) Ti 4+ silver Ag + copper (II) Cu 2+ nickel (III) Ni 3+ tin (II) Sn 2+ zinc Zn Polyatomic ions must be practiced, learned and memorized. In the table below, write the symbol for each polyatomic ion with its correct charge. ammonium hypochlorite hydroxide sulfite Sulfate nitrite NH4 + ClO - OH - SO3 2- SO4 2- NO2 - bicarbonate permanganate nitrate phosphite chlorate uranyl (hydrogen carbonate) HCO3 - MnO4 - NO3 - PO4 3- FO3 - UO2 2+ hypoiodite IO - dichromate Cr2O7 2- phosphate PO4 3- chromate CrO4 2- acetate C2H3O2 - CH3COO - Bromite BrO2 -

4 8. So that there is no confusion, please fill in the table below with the correct ion and charge: oxide hydroxide sulfide sulfite iron (II) carbonate O 2- OH - S 2- SO3 2- Fe 2+ CO3 2- hydrogen hydride sulfate chromium (VI) iron (III) ammonium H + H - SO4 2- Cr 6+ Fe 3+ NH44 + nitride Nitrite phosphide chromate zinc manganese(iv) N 3- NO2 - P 3- CrO4 2- Zn 2+ Mn 4+ nitrate cyanide phosphate dichromate tin (IV) magnesium NO3 - CN - PO4 3- Cr2O7 2- Sn 4+ Mg Your packet includes several cards that represent different ions. The unshaded cards are cations (they have pegs on their ends. The shaded cards are the negative ions (they have notches ). The number of pegs and sections of each cation card is a positive charge; likewise, negative charges for the notches and sections on the anion cards. These cards can be used to represent any ion with the same charge that the card represents. You will use the cards for the next few sections of the packet, and you may use them whenever you think you might need help determining a formula. But, it s a rare chemist, indeed, who carries around a deck of cards to determine the formula of a compound. No fear, you ll understand and be able to leave the cards behind. 10. Use your cards to model the following compounds, arrange the cards so that all of the pegs and notches are used up. Draw the resulting models and write the formulas when you are finished. a. lithium fluoride LiF b. aluminum nitride AlN c. ammonium iodide NH4I d. magnesium thiosulfate MgS2O3 d. iron (II) sulfate FeSO4 e. nickel (III) phosphate NiPO4 11. What is the pattern you see with all of these compounds? In all of these compounds the cation charge is equal and opposite to the anion charge; the resulting compound has a 1:1 ratio of cations to anions.

5 12. Now make the following compounds using the cards as models. Draw the models you make. a. lithium oxide b. aluminum sulfide c. nickel (III) chloride Li2O d. magnesium bromide Al2S3 f. lithium tartrate NiCl3 f. iron (II) phosphide MgBr2 Li2C4H6O6 Fe3P2 13. What do you notice about these compounds? The charges are not equal and opposite; the ratio of ions is not 1: When the ions in an ionic compound don t match by charge (e.g., 2+ vs 2-), we use the criss-cross method to get a formula that results in TOTAL charge being neutral (total positive = total negative) Consider Aluminum Sulfide Al 3+ S 2- The charge value is used as the subscript for the other ion. So Subscript Cation x Charge Cation + Subscript Anion x Charge Anion. In this case, 2x x2 - = 0 (The charges are balanced and the compound is neutral.) 2 3 Al 2 S 3 Notice that we only criss-cross the number not the sign of the charge. 15. In items 12 and 13, the ratios of cations to anions is not one-to-one, and therefore, we can criss-cross the charge numbers (not the signs) to determine the correct formula. When is criss-crossing not appropriate and why not? 16. Draw the model for chromium (IV) oxide. Write the formula CrO2 Now, criss-cross the charges for this compound. Write the formula Cr2O4 Why are they not the same? The criss-cross method is a short cut to a formula for a neutral compound, but not necessarily the correct formula.

6 Which one is correct? CrO2 is the correct formula; ionic compound formulas are always in their lowest ratio, so criss-cross, then reduce if possible. 17. Now consider the following compounds, ammonium sulfide and magnesium hydroxide. Make the models. How many ammonium ions are needed in the ammonium sulfide compound? _2 How many hydroxides in the other compound? _2. How do we indicate that there are multiple polyatomic ions? We indicate multiple polyatomic ions in a formula by using a parenthesis and a subscript. Consider the polyatomic ion a package and the parenthesis and subscript counts how many of that package are in the compound. When do we use and not use parentheses with ionic compound formulas? We only use a parenthesis when there are more than one of a polyatomic ion, we do NOT use a parenthesis when there is only one of polyatomic in the formula. 18. LET s PRACTICE!!!! Write the formulas of the following compounds. You might want to use scratch paper to work out the formula (i.e., criss-cross ). Attach any worksheet you use, please. a. calcium permanganate Ca(MnO 4) 2 b. ammonium dichromate (NH4)2Cr2O7 c. zinc carbonate ZnCO 3 d. lithium bicarbonate LiHCO 3 e. molybdenum (III) chlorate Mo(ClO3)3 f. magnesium nitrate Mg(NO 3) 2 g. cesium arsenate Cs3AsO4 h. strontium chlorate Sr(ClO3)2 i. uranyl nitride (UO2)3N2 j. aluminum selenide Al2Se3 k. cobalt (III) carbide Co 4C 3 l. zinc chloride ZnCl 2 m. lead (II) phosphide Pb 3P 2 n. rubidium phosphite Rb 3PO 3 o. potassium tartrate K 2C 4H 6O 6 p. aluminum cyanide Al(CN) 3 q. silver phosphate Ag 3PO 4 r. barium acetate Ba(C 2H 3O 2) 2 s. nickel (II) sulfate NiSO 4 t. mercury (II) bromate Hg(BrO 3) When naming ionic compounds, just name the ions in order, cation anion. Name the following compounds: a. NaI sodium iodide b. Sr3(PO4)2 strontium phosphate c. MgS magnesium sulfide d. (CH3NH4)3N methylammonium nitride e. UO2(ClO3)2 uranyl chlorate f. Li2O lithium oxide g. Al(OH)3 aluminum hydroxide h. Zn(CN)2 zinc cyanide i. BeF2 beryllium fluoride j. K2S2O3 j potassium thiosulfate

7 20. Remember, that the name of the multi-valent metal cations includes the roman numeral defining its charge. a. CuCl2 copper (II) chloride b. Ni3N2 nickel (II) nitride c. CrS chromium (II) sulfide d. Ag3P silver phosphide e. Ti(NO3)2 titanium (II) nitrate f. Fe2O3 iron (III) oxide g. FeO iron (II) oxide h. Zn(CN)2 zinc cyanide i. ZrBr2 zirconium (II) bromide j. V2(SO4)5 vanadium (V) sulfate 21. A student wrote the formula Fe3Cl for iron (III) chloride. Explain his error and write the correct formula. The student thought that the roman number indicates how many cations in the formula. The R.N. indicates the charge on the cation. FeCl A student saw the formula NiC2O4 and named it nickel (IV) oxalate. Explain her error and write the correct name. The student thought the 4 in the formula (the last subscript) was the result of criss-crossing charge values. The actual charge on the nickel ion is 2+, so the name is nickel (II) oxalate. 23. Ionic compounds are often made by combining a metal with a nonmetal. Explain why NH4Cl is actually an ionic compound, even though the formula does not contain a metal. Although there is no metal present, ammonium is still a cation; electrons have been transferred and the attraction between ammonium and chloride is the same as if a metal cation were in the compound. 24. Table salt is an ionic compound. However, a solid sample of table salt does not conduct electricity. What two things can be done to allow table salt to conduct electricity? Melting ionic compounds makes them conductive 25. Explain why a solution of sugar water does not conduct electricity? dissolving salts in water make them conductive There are no charged particles in sugar and in most other covalent compounds, acids being one important exception. 26. Explain why there is no such thing as a molecule of sodium chloride? A molecule is generally a group of two or more covalently bonded atoms (non-metals, generally) where specific unique bonding is achieved. In ionic compounds (e.g., NaCl), there is no specific unique bonding arrangement. To count ionic compound particles, we use the formula unit.