Name: Period: Date: By the end of today, you will have an answer to: What are polyatomic ions and why would you reverse the criss- cross?

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1 Name: Period: Date: UNIT 4: BONDING Lesson 4: Polyatomic s and Reverse Criss Cross. By the end of today, you will have an answer to: What are polyatomic ions and why would you reverse the criss- cross? Do Now: Determine the charge of each ion in an ionic. Then use the Criss Cross Method to write the balanced ionic formula. Atom Na Cl Atom Mg S Atom K O Atom Li N Atom Ca F Atom Al O CATALYST! Polyatomic s Examine Table E in your reference table. This is a list of polyatomic ions. o Poly means: o o Atomic means: s means: Based on observations in Table E, develop a definition for polyatomic ions. Explain why you can t find polyatomic ions on the periodic table or table S? 1

2 Part I: Criss- crossing with Polyatomic s Be very careful when writing formulas for these s! Compound s Involved Formula Sodium Sulfate Magnesium Cyanide 1. Sodium and Nitrate: 4. Ammonium and Oxygen 2. Lithium and Cyanide: 5. Calcium and Nitrite: 3. Magnesium and Chromate: 6. Potassium and Thiosulfate Ca(NO 3) 2 is an ionic between a calcium ion (Ca 2+ ) and a nitrate (NO 3) ion. o Why is the nitrate ion in parenthesis? Part II: Reverse Criss Cross Try This! Suppose you are given an ionic, XCl. Could you determine one possible ion that X could be? Sometimes, determining the parent ions is a little more complicated. o Example: XCl 2 is an ionic. What element could the X represent? Cation + Anion = 0. X = Cl = XCl 2 Which group is X from? Use the reverse criss- cross method to determine the group of the unknown ion. XF 2: XO CaX 2 MgX 2

3 Name: Pd: Date: CW 4.4- Polyatomics and Reverse Criss Cross 1. Write the formulas for the following polyatomic ions. a. Hydroxide b. Phosphate c. Hydronium d. Ammonium 2. Describe, in words, what a polyatomic ion is. 3. Write the formulas for the s that form from the ions below. a. NH 4 +1 and F - 1 b. NH 4 +1 and S - 2 c. K +1 CO 3-2 d. Ca +2 and SO Use the criss- cross method to write the chemical formula for the balanced ionic. 1. Potassium and phosphate: 2. Calcium and nitrite: 3. Ammonium and Oxygen 4. Lithium and Sulfite 5. Which formula represents strontium phosphate? (1) SrPO 4 (3) Sr 2(PO 4) 3 (2) Sr 3PO 8 (4) Sr 3(PO 4) 2 3

4 6. Use the reverse criss- cross to determine the charge on the unknown ion. X 3N XBr 2 Li 2X Al 2X 3 KX CaX XNO 3 X 2SO 4 7. In the formula X 2(SO 4) 3, the X represents a metal. This metal could be located on the Periodic Table in (1) Group 1 (3) Group 13 (2) Group 2 (4) Group Element X has an electron configuration of This element will combine with the phosphate ion to form a with the formula A) XPO 4 B) X(PO 4 ) 2 C) X 2 PO 4 D) X 2 (PO4) 3 9. In the formula X 2O 5, the symbol X could represent an element in Group (1) 1 (3) 15 (2) 2 (4) Element X is in Group 2 and element Y is in Group 17. What happens when a is formed between these two atoms? A) X loses electrons to Y to form an ionic bond B) X loses electrons to Y to form a covalent bond C) X gains electrons from Y to form an ionic bond D) X gains electrons from Y to form a covalent bond. 11. Explain in words how it is possible to determine the charge of the cation (positive ion) in XF 2. 4

5 Name: Pd: Date: HW 4.4- Polyatomics and Reverse Criss Cross Use the criss- cross method to write the balanced ionic. 1. Calcium and Sulfur: Use the reverse criss- cross method to determine the charge of the unknown ion. Give an example of this type of ion. 5. K 2X 2. Aluminum and Nitrogen: 6. X(SCN) 2 3. Magnesium and Nitrate: 7. CaX 2 4. Rubidium and Phosphate: 8. X 3N Name: Pd: Date: HW 4.4- Polyatomics and Reverse Criss Cross Use the criss- cross method to write the balanced ionic. 1. Calcium and Sulfur: Use the reverse criss- cross method to determine the charge of the unknown ion. Give an example of this type of ion. 5. K 2X 2. Aluminum and Nitrogen: 6. X(SCN) 2 3. Magnesium and Nitrate: 7. CaX 2 4. Rubidium and Phosphate: 8. X 3N 5

6 9. Explain one similarity and one difference between a sulfide ion and a sulfate ion. Directions - For each question: Remember - All atoms must have a complete outer shell, balanced charges! A) Use the criss-cross method to balance the charge and determine the formula. Example: 10) Mg +2 & OH - : a) Mg(OH) 2 11) SO 4-2 and Mg +2 : 12) Na + and PO ) Ba +2 and CO ) Cu +2 and NO 3-15) NH 4 + and N Explain one similarity and one difference between a sulfide ion and a sulfate ion. Directions - For each question: Remember - All atoms must have a complete outer shell, balanced charges! A) Use the criss-cross method to balance the charge and determine the formula. Example: 10) Mg +2 & OH - : a) Mg(OH) 2 11) SO 4-2 and Mg +2 : 12) Na + and PO ) Ba +2 and CO ) Cu +2 and NO 3-15) NH 4 + and N -3 6

7 Name: Pd: Date: Exit Ticket 4.4- Polyatomics and Reverse Criss Cross 1. Write the balanced ionic between the following sets of ions. (1) Ca 2+ and OH - (2) Ammonium and oxygen 2. Determine the charge on the unknown ion, X. (3) K 2X (4) X(NO 3) 2 Name: Pd: Date: Exit Ticket 4.4- Polyatomics and Reverse Criss Cross 3. Write the balanced ionic between the following sets of ions. (5) Ca 2+ and OH - (6) Ammonium and oxygen 4. Determine the charge on the unknown ion, X. (7) K 2X (8) X(NO 3) 2 7

8 Calcium is rarely found in its elemental form, but is readily found throughout the Earth mostly in the form of rocks and minerals such as limestone (calcium carbonate), dolomite (calcium magnesium carbonate), and gypsum (calcium sulfate). It is the fifth most common element in the Earth's crust. Calcium carbonate is one of the major components of many rocks and minerals including limestone, marble, calcite, and chalk. Calcium is also found in ocean water and is about the eighth most abundant element found in the ocean. 3. Determine the chemical formula for the in limestone. 4. CaX 2 represents a different with Calcium. Determine the charge of the unknown ion. Calcium is rarely found in its elemental form, but is readily found throughout the Earth mostly in the form of rocks and minerals such as limestone (calcium carbonate), dolomite (calcium magnesium carbonate), and gypsum (calcium sulfate). It is the fifth most common element in the Earth's crust. Calcium carbonate is one of the major components of many rocks and minerals including limestone, marble, calcite, and chalk. Calcium is also found in ocean water and is about the eighth most abundant element found in the ocean. 3. Determine the chemical formula for the in limestone. 4. CaX 2 represents a different with Calcium. Determine the charge of the unknown ion. 8