Chemistry Class - Ionic Molecules - Homeschool Science Chemistry

Today we have another fun molecule experiment! This is the seventh lesson in the homeschool science Chemistry Class I am putting together for elementary and middle school aged students! Click HERE to see all the other lessons too!





Today's lesson includes a fun lab and a discussion on molecules formed with ionic bonds!

Supplies: 

* 2 bowls with water
* salt
* 3 wires with alligator clips on the ends
* 9 volt battery
* LED light


Goals:
At the end of this lesson, students will be able to...
1- Explain what a molecule is.
2- Explain what an ionic bond is.
3- Give an example of a molecule held together by ionic bonds.
4- Tell how many and which atoms are in a molecule if they are given the molecules chemical formula.

Lesson:


Read: We're going to start with an experiment today! Sometimes water will conduct electricity, and sometimes it will not. We're going to set up two solutions: one with salt dissolved in it, and one without extra salt.

Fill two beakers or bowls about 2/3 full with water. Add 1/4 cup salt to one of them. Stir until it is dissolved.

Sidenote: a solution is a liquid with something dissolved in it. One of your solutions only has the atoms and molecules that are normally in your tap water. The other solution has a lot of salt! 

Once your solutions are ready (It's okay if there is some leftover salt on the bottom of the beaker/bowl.) grab your battery, alligator clips, and led light bulbs!

Connect three alligator clips to make a circuit between an LED light, a battery, and the bowl of plain water: connect one end of one alligator clip to the positive terminal on the battery. Place the other end of the alligator clip on an LED light.  Connect another alligator clip to the other end of the LED light and place the other end of the alligator clip in the bowl of plain water. Connect the final alligator clip to the negative terminal of the battery and place the other end of the alligator clip in the bowl of plain water. Here is a diagram you can use also:



Normally, in tap water you will set this up and see nothing happen. If your tap water has a lot of salts in it the LED may turn on faintly.

Next, switch bowls with the salt water dish. The LED should turn on. Discuss for a minute or two possible reasons for why the light turned on here and not before. (tip: some LED's are directional, so if it doesn't work try turning the LED around.)

Read: Electricity is just a flow of moving electrons through a path. The battery has a lot of electrons piling up at the negative terminal because of chemical reactions in the battery. When the battery is connected in a complete circuit (or path that the electrons can travel on), the electrons quickly flow away from the "pile-up" at the negative end of the battery, through the wires, and into the positive end of the battery. As the electrons pass through the LED, they provide enough energy to turn it on. 

Normally, when the electrons hit water, they spread out and slow down so much that they do not flow quickly enough to create a circuit that will turn on the light. Adding salt to the water changes that. When we dissolve salt in water we add enough charged atoms to the water that electricity can zip right across the bowl of water and into the next wire. How does salt do this? Keep reading!

Let's look at table salt. It's chemical name is sodium chloride because it is a molecule made from sodium and chlorine atoms. Look at the diagrams of sodium and chlorine below. What do you notice about the electrons in their outer energy levels (drawn in red)?




Remember that the second energy level can hold 8 electrons. The third energy level can hold 18, but it will be stable when it has 8. Notice that sodium has only ONE electron. Chlorine NEEDS only one to be stable. 

Sodium and chlorine combine using an ionic bond: the ONE lone electron in sodium actually leaves the sodium atom and starts orbiting the chlorine atom. This gives chlorine 8 electrons in its outer energy level, which makes it stable. Chlorine still has the same number of protons that it started with, so now it has ONE MORE electron than protons. Since electrons have a negative charge, the chlorine atom now has a "-1" charge! It is written "Cl-".  Since sodium lost an electron, it now has one more proton than electrons, giving it a "+1" charge! It is written "Na+" We call atoms with a charge "ions."

Just like the positive end of a magnet is attracted to the negative end of another magnet, the positive sodium is attracted to the negative chlorine. As the positive and negative ions come close together, they form a strong bond, the "ionic bond." 

This ionic bond is what holds sodium chloride, or table salt together. The positive and negative ions line up alongside each other forming a 3-D pattern like this:



If you look at a salt crystal under a microscope, it will look cube-ish because the sodium and chloride ions line up in rows and sheets.

Remember how water molecules are polar (or have positive and negative sides)? When you place salt in a bowl of water, the sodium and chlorine ions separate from each other and are surrounded by water.

When you connected the circuit through the bowl of salt water at the beginning of this lesson, the electrons that flowed from the battery were able to easily skip across the charged ions in the water.

You can test other items in your kitchen to see if they are held together by ionic or covalent bonds! Simply dissolve them in a bowl of water, and see if they will conduct electricity! Usually salts (including baking soda) will conduct electricity because they are made from ions that are attracted by opposite charges. Other chemicals (like sugar and cornstarch) are held together by covalent bonds--dissolving them in water will not create ions and the electricity will not be able to flow across the bowl.

BONUS DISCUSSION:
Look at your periodic table. What other elements have only one electron in their outer energy level? (All the elements in the same group as sodium--Group 1.) They are all extremely reactive because that one electron is often transferred to another atom.

What other elements need only one electron to be stable? (All the elements in the same group as chlorine--Group 17.)  These are also extremely reactive but, once they get their one extra electron are extremely stable. 

Fun fact: Potassium chloride is a salt substitute made from potassium and chlorine. Where is potassium on the periodic table? How is it similar and different than sodium? 

Review/Final Discussion:


1- What is an ion?
2- How many electrons fit in the lowest energy level? In the second energy level? In the third energy level?
3- How many electrons does the third energy level require to act stable?
4- What is an ionic bond? (a bond formed when atoms with opposite charges are attracted to each other after electrons have been transferred from one atom to the other)
5- How can you test a kitchen chemical to see if it is held together by ionic or covalent bonds?

***

This is the seventh lesson in my Atoms & Molecules Chemistry Class for homeschoolers!  Click HERE to get the rest!






And if you're looking for more homeschool unit studies, be sure to check out our growing collection here!



Happy Educating,
Carla & the kids who don't sit still!





And if you're looking for more homeschool unit studies, be sure to check out our growing collection here!



Happy Educating,
Carla & the kids who don't sit still!

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