Ions and Ionic Compounds

Transcription

1 Ions and Ionic Compounds Elements combine in a specific ratio to form compounds. Compounds can be categorized as ionic or covalent depending on the type of bond present within the compound. Ionic compounds consist of ionic bonds that arise from the electrostatic (magnetic) attraction between ions (charged species). The positively charged ion, called a cation, and the negatively charges ion, called an anion are attracted much like two magnets. The bond found in covalent molecules is a covalent bond which results from two atomic nuclei sharing electrons. This exercise is designed to allow you to explore the world of ionic compounds. When you complete this exercise you should understand: 1. Which elements form cations and which elements form anions. 2. Be able to list all metals that form cations of a specific charge and identify that charge. 3. Be able to list all elements that form anions and identify the charge they will have. 4. Be able to name cations, anions, and polyatomic ions. 5. Be able to determine the number of protons and electrons in an element and an ion. 6. Explain the difference between elemental ions and polyatomic ions. 7. Be able to explain what the term charge neutrality means. 8. Be able to write the formula of ionic compounds. 9. Be able to write the name of ionic compounds. Part I: Ions A cation results from an element losing an electron (e ) to form a positively charged species. The magnitude of the charge of the cation depends on the number of electrons lost. X X + + e X X e The number of electrons lost by an element, that forms a cation, equals the electron difference between that of the element and that of the nearest noble gas or pseudo noble gas. Example: Sodium, in its neutral state, has 11 protons and 11 electrons. The nearest noble gases are Neon with 10 electrons and Argon with 18 electrons. Sodium can either lose one electron to have the same number of electrons as Neon, or it can gain 7 electrons to reach Argon. Because the difference between Sodium and Neon is less, Sodium will lose one electron. Once sodium has lost an electron the ion will

2 contain 11 protons but only 10 electrons making the Sodium ion have a 1+ charge. An anion is the product of an element gaining electrons to become negatively charged. The magnitude of the charge of the anion depends on the number of electrons gained. Z + e Z Z + 2e Z 2 The number of electrons gained by an element, that forms an anion, equals the difference between that element and the nearest noble gas. Example: Chlorine has 17 protons and 17 electrons in its neutral state. The nearest noble gases are Neon with 10 electrons and Argon with 18 electrons. Chlorine can either lose 7 electrons to reach Neon or it can gain one electron to have the same number of electrons as Argon. Because the difference between Chlorine and Argon is less, Chlorine will choose to gain one electron. After the addition of that electron, Chlorine will have 17 protons and 18 electrons making the Chlorine ion have a 1 charge. Part I of this lab allows you to identify the type of element (metal, metalloid, nonmetal) that forms cations. You will find that cations can be of two types. You will identify the two types of cations and learn how to name them. Additionally, you will discover that anions can be of two types. One type of anion is referred to as a polyatomic anion. Poly meaning many, atomic meaning atom, hence, they are many atom ions. A list of polyatomic ions is provided at the end of this exercise. The elemental ratio, charge and name of each polyatomic ion are set. Alteration of any single piece of the above information and you alter the ion. The second type of anion is an elemental anion. You will identify the type of element that forms elemental anions, identify the periodic trend associated with the charge formed, and learn how to name these anions.

3 Part I: Ions 1. Define cation. 2. Define anion. 3. Define ionic bond. 4. Cations are charged species that result from the of electrons. 5. Anions are charged species that result from the of electrons. Separate the cards (symbol up) according to color, elemental symbol, and charge. 6. Besides hydrogen and the polyatomic ion ammonium, what type of element forms cations: metal, metalloid, nonmetal? Analyze the elemental symbol side of the pink cards and orange cards for differences. 7. Describe the difference between the cations represented on the pink cards and those found on the orange cards.

4 Flip the pink and orange cards over. 8. Do you notice a difference in how the cations on the pink cards are named compared to those on the orange cards? a. A cation for which the charge is constant is named by writing the. b. A cation that can have more than one charge is named by writing first the followed by the charge as a. 9. Using your text or the notes, list the symbols of all of the elements that form cations for which the charge is constant, the magnitude of that charge, and the name of those cations. 10. What periodic trends do you observe for group 1 and group 2 elements? Analyze the elemental symbol side of the green cards and yellow cards for differences. 11. Describe the difference between the symbols of anions on the green cards compared to those on the yellow cards. 12. What type of element form anions: metals, metalloids, or nonmetals?

5 Flip the yellow and green cards over. 13. What do the names of the elemental anions have in common? 14. Using your text or the notes, list the symbols of all elements that form anions, the magnitude of that charge, and the name of the anion. 15. What periodic trend do you observe with the elemental anions? 16. What type of ions found on the yellow cards? 17. Define polyatomic ion.

6 Additional Practice Element Atomic Number # protons # electrons in neutral atom Will the element gain/lose electrons during ion formation # of electrons in ion Ionic Charge Symbol of Ion Name of ion Sodium Lose Na + Sodium ion Oxygen Cesium Barium Fluorine Selenium Phosphorus Potassium Radium Iodine

7 Part II: Formulas of Ionic Compounds Ionic compounds are the result of cations combining with anions via an electrostatic attraction. The ionic compound formed will be neutral. To obtain charge neutrality all positive charges must be counterbalanced by an equal amount of negative charge. Example: Sodium ion carries a 1+ charge, the chloride ion carries a 1 charge. When sodium reacts with chlorine, it does so in a 1:1 ratio making sodium chloride neutral. Example: Magnesium ion carries a 2+ charge, the oxide ion carries a 2 charge. When magnesium reacts with oxygen, it does so in a 1:1 ratio making magnesium oxide neutral. A third example is the reaction of sodium ion with oxide ion. Again sodium has a 1+ charge and the oxide a 2 charge. When sodium combines with oxygen it must do so in a 2:1 ratio to give neutral sodium oxide. Note: When more than one of an ion is required for the ionic compound to achieve charge neutrality, a subscript is used to the right of the elemental symbol to indicate the quantity of that ion necessary. If more than one polyatomic ion is needed for the ionic compound to achieve charge neutrality then the polyatomic ion is placed in parenthesis and the number required is written as a subscript outside the parenthesis. To assist in determining when an ionic compound achieves charge neutrality the ions in the ionic block set have been designed in such a way so that the size is related to the magnitude of the charge. Begin by placing the cation of interest on a surface. Then add anions one by one until the size of the cation row and anion row are equivalent (or at least really close). Example: A compound of magnesium ion and chloride ion. If you lay the magnesium ion down followed by one chloride ion, you will notice that the sizes do not match. Now add a second chloride ion and you will see that the sizes match. That is

8 because it takes 2 chloride ions of a 1 each to neutralize the charge of one magnesium ion. Your cards will look as below. Part III: Naming Ionic Compounds The name of an ionic compound is simply the combination of the names of the ions. The name is written with the cation listed first followed by the name of the anion. In this section of the lab you will practice developing chemical formulas for and naming ionic compounds. In so doing you will explore the concept of charge neutrality. For each of the following pairs, 1. Gather the cations and anions of indicated by the first cation/anion pair on the attached table. 2. Place the cation on your desk with the symbol face up. 3. Starting on a second row, add anions until the length of the anion row is equivalent to that of the cation row. 4. If in adding anions the anion row becomes longer than the cation row, add an additional cation and repeat step Fill in the table with your results. 6. Repeat steps 15 for each cation and anion pair in the table.

9 Cation/Anion Pair Symbol of the Cation Symbol of the Anion # of Cations Required For charge neutrality # of Anions Required For charge neutrality Formula of Compound Name of Compound 1 Potassium and bromide Iron (III) and oxide Magnesium and hydroxide Gold (III) and sulfate 5 Aluminum and nitride 6 Copper (II) and acetate 7 Calcium and sulfide 8 Sodium and phosphate

10 Practice Problems In the table below write the symbols of the positive and negative ions using the periodic table to determine ionic charge. Determine the number of each ion that will give a charge balance by using the cards to help match positive and negative charges. Write correct formulas using subscripts to indicate when two or more ions are needed. Write the names of the ionic compounds by placing the metal name first, then the nonmetal name ending in ide. Name Positive ion Negative ion Formula Sodium oxide Magnesium sulfide Potassium chloride Calcium nitride Aluminum bromide Lithium phosphide Cadmium nitride Silver oxide

11 Name the following ionic compounds. Formula Na 2 S Name ZnF 2 MgO K 3 N Ca 3 P 2 AlBr 3 Write the ionic formula for the following compounds. Name Positive ion Negative ion Formula Iron (II) bromide Copper (I) oxide Gold (III) nitride Copper (II) chloride Gold (I) phosphide Iron (III) sulfide

12 Name the following ionic compounds. Formula Cu 3 P Name Fe 2 O 3 FeBr 3 CuCl AuN Write the ionic formulas for the following compounds containing polyatomic ions. Name Positive ion Negative ion Formula Sodium acetate Iron (III) cyanide Gold (I) dichromate Calcium hydroxide Aluminum phosphate Barium nitrate

13 Test Yourself Name: In each of the following squares write the formula for the compound and its name. Cs + Sr 2+ Sc 3+ Cr 3+ Co 2+ Ti 4+ Ru 3+ Se 2 I F CrF 3 Chromium (III) fluoride C 2 O 4 2 Ti(C 2 O 4 ) 2 Titanium (IV) oxalate ClO 3 MnO 4 PO 3 3

14 Polyatomic Ions CN OH O 2 2 NH 4 + H 3 O + cyanide hydroxide peroxide ammonium hydronium Carbon C 2 H 3 O 2 2 C 2 O 4 CO 3 2 HCO 3 Nitrogen NO 3 Silicon SiO 3 2 Phosphorus 3 PO 4 2 HPO 4 H 2 PO 4 Sulfur SO 4 2 HSO 4 acetate oxalate carbonate hydrogen carbonate (bicarbonate) nitrate NO 2 silicate 3 phosphate PO 3 hydrogen phosphate dihydrogen phosphate 2 sulfate SO 3 hydrogen sulfate HSO 3 nitrite phosphite sulfite hydrogen sulfite Chlorine ClO 3 ClO 4 Manganese MnO 4 Chromium CrO 4 2 Cr 2 O 7 2 chlorate ClO 2 chlorite perchlorate ClO hypochlorite permanganate chromate dichromate