ANSWER KEY Energy Levels, Electrons and IONIC Bonding It s all about the Give and Take! From American Chemical Society Middle School Chemistry Unit: Chapter 4 Content Statements: Distinguish the difference between an ionic and covalent bond and/or compound. Name an ionic or covalent compound given the chemical formula, and write the chemical formula given the name of the compound. INSTRUCTIONS: Read the material in black, watch the animations, and answer the BLUE questions as you go. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ INTRODUCTION: Chlorine is a greenish poisonous gas and sodium is a shiny, soft, and very reactive metal. The drop of water shown in the helps expose the atoms at the surface of the sodium so that they can reactive with the chlorine. This type of bond releases a lot of energy in the form of heat and light. Watch this video clip showing sodium metal reacting with chlorine gas and answer the question below. 1. What compound is formed when chlorine gas and sodium metal are allowed to bond ionically? ANSWER: NaCl table salt 2. In the last lesson we learned that covalent bonds occur when two non metals share electrons in order to bond. What makes this ionic bond different from a covalent bond? Think about the types of elements that are forming the ionic bond. ANSWER: this bond takes place between a metal (Sodium) and a non metal (Chlorine)
Watch this animation showing how the electrons behave during the ionic bond between sodium and chlorine. Note: this is a simplified view of the ionic bond between sodium and chlorine. In reality the chlorine atom would be bonded to another chlorine atom as part of the gas Cl 2. The sodium atom would be one of billions of trillions of sodium atoms bonded together as a solid. The combination of these substances is a complex reaction between the atoms of the two substances.this animation shows single separated atoms to illustrate the idea of how ions and ionic bonds are formed. The attraction of the protons in the sodium and chlorine for the other atom s electrons brings the atoms close together. Chlorine has a stronger attraction for electrons than sodium (shown by the thicker arrow). At some point during this process, an electron from the sodium is transferred to the chlorine. The sodium loses an electron and the chlorine gains an electron. 3. When an atom gains or loses an electron, what does it become? (Hint: they can be positive or negative)? ANSWER: ions During this ionic bond between sodium and chlorine, sodium loses an electron. Fill in the chart below to show how sodium changes when it bonds with chlorine. Watch the animation again if it helps. 4. Fill in the chart below: Sodium after it ionically bonds with chlorine: Chlorine after it ionically bonds with sodium: protons 11 protons 17 electrons 10 electrons 18 charge +1 charge 1 number of energy levels before the bond number of energy levels after the bond 3 number of energy levels before the bond 2 number of energy levels after the bond 3 3
During an ionic bond, atoms gain or lose electrons until their outer energy level (outer shell) is full. For example, when sodium loses its on outer electron from the third energy level, the second level becomes the new outer energy level and is full. Since these electrons are closer to the nucleus, they are more tightly held and will not leave. When chlorine gains an electron, its third energy level becomes full. An additional electron cannot join, because it would need to come in at the fourth energy level. This far from the nucleus, the electron would not feel enough attraction from the protons to be stable. The positive sodium ion (cation) and negative chlorine ion (anion) attract each other and form an ionic bond. The ions are more stable when they are bonded than they were as individuals atoms. Now YOU explain it! 5. What is the basic difference between covalent and ionic bonding? ANSWER: during an ionic bond, metals and nonmetals bond and electrons are either gained or lost by each atom to form ions instead of shared. 6. Write captions for each picture to describe the process of ionic bonding. Caption for picture #1: Sodium and chlorine atoms are near each other
Write a caption for picture #2 of sodium bonding with chlorine: (be sure to include mention of why there is a thicker arrow. ANSWER: the protons (nucleus) of the 2 atoms attract the electrons of the other atom. The thicker arrow shows that chlorine has a stronger attraction for electrons than sodium has. Write a caption for picture #3 of sodium bonding with chlorine: ANSWER: During the interactions between atoms, the electron in sodium s outer energy level (shell) is transferred to the outer energy level of the chlorine atom. Write a caption for picture #4 of sodium bonding with chlorine: ANSWER: since sodium lost an electron, it has 11 protons, but only 10 electrons. This makes sodium a positive ion with a charge of +1. Since chlorine gained an electron it
has 17 protons and 18 electrons. This makes a negative chloride ion with a charge of 1. Write a caption for picture #5 of sodium bonding with chlorine: ANSWER: the positive sodium ion and the negative chloride ion attract one another. They make an ionic bond and form the ionic compound NaCl. Watch this animation showing the lattice structure of NaCl and answer the questions that follow. 7. What ion is the larger green ball (it has a negative charge)? ANSWER: chloride ion 8. What made it a negative ion? ANSWER: it gained an electron from the sodium atom 9. What is the smaller grey ion (it has a positive charge)? ANSWER: sodium ion 10. What made it a positive ion? ANSWER: it lost an electron gave it up to chlorine ACTIVITY! Materials: Salt grains on a piece of black paper Salt left in container after salt water is allowed to evaporate 2 small balls made out of clay 2 large balls made out of class
2 toothpicks Procedure Part 1 Observe sodium chloride crystals. A. Place a few grains of salt on a piece of black paper. Use your magnifier to look closely at the salt 11. Describe what you see ANSWER: cubic structure of each salt crystal B. Use your magnifier to look at the salt crystals in the petri dish (these resulted from the evaporation of salt water). 12. Describe what you see ANSWER: cubic structure of the salt left behind after evaporation of the water. Part 2: Make NaCl units. A. Use the clay to make 2 small balls (the size of a small marble) and mark them with a toothpick with a + which represent the positive sodium ions. B. Use the clay to make 2 larger balls (the size of a large marble) and mark them with a toothpick with a which represent the negative chloride ions. C. Break two toothpicks in half. Use one of the half toothpicks to connect the centers of the small and large ions together to make a unit of sodium chloride (NaCl). Do the same thing with the other small and large ball. D. Use another half toothpick to connect the two NaCl units in a straight line as shown below: E. Contribute your line of ions to your group and arrange them to make a 4 4 square of ions.
F. Use half toothpicks to attach the ends of each line to hold the ions together. You only need to place toothpicks in the balls at the end of each line. G. Build a class sodium chloride crystal combine your group s layer of ions to the other groups layer of ions to build a model of a sodium chloride crystal. 13. Describe what you see. ANSWER: Anywhere you look on the crystal, a sodium ion and a chloride ion are always surrounded by the oppositely charged ion. These opposite charges hold the ions together in a crystal lattice shape. 14. Knowing what you do about sodium and chloride ions, why are salt crystals cube shaped? ANSWER: The size and arrangement of the ions forms a cube on the molecular level. Since the pattern repeats over and over again in the same way, the shape stays the same even when the crystal becomes the normal size that we can see. TAKE IT FURTHER: There is another common substance called calcium chloride (CaCl2). It is the salt that is used on icy sidewalks and roads to melt the ice. When calcium and chlorine react they produce ions, like sodium and chlorine, but the calcium ion is different from the sodium ion. 15. What ions make up CaCl 2? ANSWER: One calcium ion and two chloride ions
Watch the animation of the calcium chloride bond taking place. 16. Write a caption for each picture to briefly describe the process of ionic bonding between calcium and chloride ions. Caption for picture #1: one calcium atom and two chlorine atoms are near each other. Write a caption for picture #2: Be sure to make mention of why the arrows are thicker. ANSWER: the protons (nucleus) of the calcium atom attract the electrons from the
chlorine atoms. The protons (nucleus) of the two chlorine atoms attract the electrons from the calcium atom more strongly as shown by the thicker arrows. Write a caption for picture #3: ANSWER: During the interactions between the atoms, the two electrons in calcium s outer energy level (shell) are transferred to the outer energy level (shell) of each of the chlorine atoms. Write a caption for picture #4: Make mention of why the chloride ion has a 1 charge and why the calcium ion has a +2 charge. ANSWER: Since calcium lost two electrons, it has 20 protons, but only 18 electrons. This makes calcium a positive ion with a charge of 2+. Since each chlorine atom gained an electron, they each have 17 protons and 18 electrons. This makes each chloride a negative ion with a charge of 1.
Write a caption for picture #5: ANSWER: oppositely charged ions attract each other, forming an ionic bond. The bonded ions are more stable than the individual atoms were. 17. Write a definition for ionic bond which includes mention of the type of element that form these bonds as well as the behavior of the electrons in an ionic bond. ANSWER: an ionic bond occurs between metals and nonmetals in which electrons are either gained or lost to create oppositely charge ions which are attracted to each other to form an ionic bond. 18. What is the difference between a covalent bond and an ionic bond? ANSWER: ionic bonds involve the gain or loss of electrons to fill the outer energy levels instead of sharing electrons to fill the outer energy levels. Ionic bonds occur between metals and nonmetals, covalent bonds occur between two nonmetals.