# Periodicity of the Periodic Tabl

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```					GK12 Module Teacher’s Guide

Periodicity of the Periodic Table
Morgan Perrone Abstract: Using demonstrations, students will understand how the periodic table is set up and how the number of electrons an element has affects its properties and the compounds it can form. An experiment that separates three different compounds into their elements will help students understand what charged particles are, how electricity works, and how elements are arranged in the periodic table. Grade Level(s): 8th-12th Objectives:  To understand that the periodic table is set up according to the number of electrons that are in each element’s outer shell and how this affects the properties of the elements  To recognize that when elements combine they share electrons, which allow them to either give away or take “extra” electrons when they separate (making charged ions).  To understand that current is the flow of electricity and that there are positive and negative sides that attract the opposite charge.  To generate hypotheses, test them, and record observations.  To graph the observations and discuss and understand what the graph means. National Standards: Standard Standard Standard Standard Standard A: Science as Inquiry; Abilities necessary to do scientific inquiry A: Science as Inquiry; Understandings about scientific inquiry B: Physical Science; Properties and changes of properties in matter B: Physical Science; Transfer of energy G: History and Nature of Science; Nature of science

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GK12 Module Teacher’s Guide

New Mexico Standards: Strand 1, Standard 1: Scientific Thinking and Practice; Use scientific method Strand 1, Standard 1: Scientific Thinking and Practice; Understand process of scientific investigation Strand 1, Standard 1: Scientific Thinking and Practice; Use mathematical ideas, tools, techniques Strand 2, Standard 1: Physical Science; Forms and properties of matter Strand 2, Standard 1: Physical Science; Transfer, change, and conservation of energy Materials:                Na(NO3)1 (0.2M solution; 1.7g in 100mL water)* Ca(NO3)2 (0.2M solution; 3.3g in 100mL water)* Fe(NO3)3 (0.2M solution; 4.8g in 100mL water)* Balance and weigh paper Wire with alligator clips attached to each end (2 wires, 4 clips) A block of wood with two nails (2.5inches long) that are 1cm apart Multimeter 6V Battery 150mL beaker (3) Rinse bottle Kimwipes Waste beaker Scoopula/spoon Small light bulb (optional) Deionized water

*

weigh and add the salts to the water for the students

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GK12 Module Teacher’s Guide

Periodic Table of the Elements

Background: The atomic number on the periodic table refers to the number of protons an element has. For example, carbon, which as an atomic number of 6, has 6 protons. The number of protons an element has is also equal to the number of electrons that element has. Thus, carbon has 6 electrons as well as 6 protons. Protons have a positive charge and are found in the nucleus of an atom, along with neutrons, which have no charge. The nucleus is positively charged, while electrons, which orbit the nucleus, are negatively charged.

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GK12 Module Teacher’s Guide

It is the electrons that allow chemical reactions and compounds to form, as they are not bound up in the nucleus. Not all electrons, however, can participate in these reactions. The electrons closest to the nucleus feel the positive charge of the nucleus, and because electrons are negatively charged, they remain near the nucleus rather than take part in chemical reactions. Electrons tend to orbit the nucleus at different levels, known as orbitals. Each orbital must be filled with electrons before the next orbital can be filled. For example, the first orbital can hold 2 electrons and must be filled before it can go to the second orbital, which can hold 8 electrons. It is because of this rule that trends can be seen in elements across the periodic table, known as periods, and down the periodic table, known as groups. For example, if this rule is applied to Lithium (atomic number 3), 2 electrons must fill the inner orbital, and there is one electron left to fill the outer orbital. If this is continued across the period, each element gains one electron, and therefore has one more electron in its outer orbital. Thus, across period 2, the outer electrons are as follows: Element At. No. lithium 3 beryllium 4 boron 5 carbon 6 nitrogen 7 oxygen 8 fluorine 9 neon 10 Inner Orbital 2 2 2 2 2 2 2 2 Outer Orbital 1 2 3 4 5 6 7 8

• • • • • • • •

This pattern continues for period 3, though an extra middle orbital that can hold 8 electrons must be added. For example, sodium (atomic number 11) has 2 electrons in the inner orbital, 8 in the middle orbital, and 1 left over for the outer orbital.

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GK12 Module Teacher’s Guide

• • • • • • • •

Element At. No. sodium 11 magnesium 12 aluminum 13 silicon 14 phosphorus 15 sulfur 16 chlorine 17 argon 18

Inner 2 2 2 2 2 2 2 2

Middle 8 8 8 8 8 8 8 8

Outer 1 2 3 4 5 6 7 8

Periods become more complex past period 3; however, it is only required of 6th-8th graders that they understand the periodic table trends up to period 3. Compounds, which are substances made of two or more elements formed by a chemical reaction, are formed when two or more atoms combine. This happens because atoms want to be stable, and the only way to be completely stable is to have their orbitals be as full as possible. This can mean an element has 8 electrons in the outer orbital, or has no electrons in the outer orbital, but has 2 electrons in the inner orbital. Thus the noble gases, which are the last group of elements on the periodic table, are the most stable elements because their orbitals are completely full. The rest of the elements are not as stable, and they tend to either give up or take electrons in order to become stable. The electrons that bond to another atom are known as valence electrons, and they are the ones responsible for chemical reactions. These are the electrons that are actually shared, given up or taken. For example, lithium, which has only one electron in its outer orbital, must give up one electron to become stable. Thus, lithium’s valence is one. Nitrogen, on the other hand, has 5 electrons in its outer orbital and needs 3 electrons in order to become stable. So nitrogen’s valence is three.

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GK12 Module Teacher’s Guide

Element • lithium • beryllium • boron • carbon • nitrogen • oxygen • fluorine • neon

At. No. 3 4 5 6 7 8 9 10

Inner 2 2 2 2 2 2 2 2

Outer 1 2 3 4 5 6 7 8

Valence 1 2 3 4 3 2 1 0

This trend also continues for period 3: Element sodium magnesium aluminum silicon phosphorus sulfur chlorine argon At. No. 11 12 13 14 15 16 17 18 Inner 2 2 2 2 2 2 2 2 Middle 8 8 8 8 8 8 8 8 Outer 1 2 3 4 5 6 7 8 Valence 1 2 3 4 3 2 1 0

• • • • • • • •

The alkali metals (group 1) and the halogens (group 17) are some of the most unstable elements. The alkali metals have 1 electron in an orbital that can hold 8, while the halogens have 7 electrons in an orbital that can hold 8. Thus, the alkali metals tend to give up their 1 electron while the halogens tend to accept 1 electron very readily. These elements are very reactive and tend to produce violent reactions when combined. The reactivities of the elements tend to decrease across periods, increase for groups 16 and 17, and then decrease at the noble gases. The transition metals, which are found in the middle of the periodic table, take a longer time to react, and the reactions do not tend to be violent. For example, the rusting of iron is a chemical reaction that takes some time and does not produce a violent reaction. Other combinations of elements can be seen by looking at the periodic table, and they react to produce a variety of compounds.

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GK12 Module Teacher’s Guide

Valence electrons are important in determining what chemical reactions can take place between elements, and they are also important in understanding the physical properties of each of the elements. Each group of elements has the same number of valence electrons (for example, group 1 elements all have a valence of one); thus they each have similar physical properties. For example, when group 1 elements are combined with group 17 elements, they tend to produce salts that all look very similar; in fact, there is no way to tell these salts apart by just looking at them. They all tend to look, taste, and feel like sodium chloride, or table salt. When electrons are given up or taken from one element or combination of elements to another element or combination of elements, charged particles known as ions are formed. For example, when sodium combines with chlorine to form sodium chloride, the sodium atom gives up one electron and the chlorine atom takes this electron. Thus, the sodium atom becomes positively charged because it has given up one electron and now has an extra positively charged proton, and the chlorine atom becomes negatively charged because it accepts one extra negatively charged electron. Although sodium chloride is overall neutrally charged, if the compound were to split, the sodium would permanently give up its one electron and the chlorine would permanently have the extra electron, which makes them both ions. These ions could combine to form other compounds, which would again be neutral. Demonstrations These demonstrations show the reactivity of the alkali metals, the non-reactivity of the noble gases, and the similar properties of groups.

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GK12 Module Teacher’s Guide

Reactivity of Sodium
Materials

 250mL or 500mL clear graduated cylinder  paint thinner  Pure sodium stored in paint thinner/oil Caution: Sodium is a very reactive and dangerous element. Check with your school to see whether or not it is even allowed in the school.  water  forceps  knife Procedure 1. Pour the graduated cylinder a third full of water 2. Pour the graduated cylinder another third full of paint thinner 3. Take the sodium out of the container using the forceps. Place the sodium on a paper towel and cut a pea size piece with the knife. Notice the metallic inside of the sodium and how quickly it oxidizes when exposed to air. 4. Place the left over sodium back in the jar. Put the small, cut piece of sodium in the graduated cylinder, and observe the reaction. 5. As the sodium reacts with the water, the sodium combines with the oxygen and hydrogen to form sodium hydroxide, and hydrogen gas is released. 6. Allow all the sodium to react with the water before disposing of the solution.

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GK12 Module Teacher’s Guide

Non-reactivity of the Noble Gases
Materials   

Neon light Generator Regular light bulb

Procedure Neon is used in neon lights, while Argon is used in regular light bulbs, and Krypton can also be used in lights. All of these are noble gases, which means they are not reactive. Plug in the generator and turn on the neon light or turn on the regular light bulb. Discuss why it is a good idea to use noble gases for making light (they do not react under most conditions, and putting a current through them will not cause them to form new compounds or to have violent reactions like the sodium).

Similar Properties of Groups
Materials    

Sodium chloride Sodium bromide Potassium chloride Potassium bromide

Procedure 1. Have the students look at these four salts and compare them. Just by looking at them, they should not be able to see any differences between them. Discuss why that is (they are found in the same groups, and therefore have similar properties.). 2. Discuss what you could do to tell them apart (measure density and melting point).

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GK12 Module Teacher’s Guide

References: Umland, Jean B., and Jon M. Bellama. General Chemistry. 2nd ed. St. Paul: West Publishing Company, 1996. Experiment Procedures: 1. Before starting this experiment, have the students figure out what the charges of the sodium ion (+1) and the calcium ion (+2) are. If you let them know that each chemical formula is electrically neutral, they may be able to figure out what the nitrate ion’s charge is (-1). They can try to guess the iron ion’s charge based on the pattern (+1, +2, and iron is +3). 2. Hammer the 2.5 inch nails into the block of wood; make sure the nails are 1cm apart. 3. Each alligator clip has a nail screwed into it; wind one of the wires around the screw of one alligator clip, and then wind the other end of the wire around the screw of another alligator clip. Repeat this with the other wire. 4. Connect one of the alligator clips to the positive end of the battery and connect the other alligator clip to one of the nails (see Figure 1). Take the other wire and connect one alligator clip to the negative end of the battery and the other alligator clip to the red wire of the multimeter. 5. Weigh out 1.7g of the sodium nitrate, and put it into a beaker with 100mL of water; you do not need to stir. 6. Put the block of wood on top of the beaker, and make sure the nails are in the water. 7. Have the students write down their hypothesis. 8. Turn the multimeter on to the side that reads Amps, and then take the black wire, and touch the metal end to the top of the empty nail. If the reading is negative, switch the wires. 9. Have the students make a chart with element name and Amps. Have them write down the amount of current in Amps and any other observations. 10. Repeat this process for calcium (3.3g) and ferric nitrate (4.8g); before each reading, have the students write down a new hypothesis.

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GK12 Module Teacher’s Guide

11. Have the students make a bar graph of the compound versus the current. 12. As an optional part of the experiment, put the light bulb in place of the multimeter and observe what happens.

Figure 1. Diagram of the periodic table experiment set-up. Conclusions: After making their graph, have the students answer these questions: 1. What can you conclude about the relationship between the charge of an element and the current that is produced? (The greater the charge, the

more current that is produced. The current nearly doubles each time the charge goes up one)

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GK12 Module Teacher’s Guide

2. Does this support or disprove each of your hypotheses? Why? 3. How might this be used to identify an element or its place on the periodic table? (A known charge could help place an element in its place in the table,

or you can figure out the charge be seeing where the element is on the table. Conductivity is one of many different ways an element can be identified.)

4. How might this have been useful for creating the periodic table of elements? (Figuring out charges of elements could have helped place the

elements in their proper place, as there is a pattern of positive and negative charges across and down the periodic table.)

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GK12 Module Glossary

1. Alkali metal – Group 1 on the periodic table; they have one outer electron and are very reactive. 2. Alkaline earth metal – Group 2 on the periodic table; they have two outer electrons and are very reactive. 3. Amps – unit for electrical current. 4. Atomic number – the number of protons in an atom, which is equal to the number of electrons. 5. Compound - substances made of two or more elements formed by a chemical reaction, which occurs when two or more atoms combine. 6. Current – flow of electric charge 7. Electron – negatively charged particle found orbiting the nucleus of an atom. 8. Group – elements going down the periodic table. 9. Halogen – Group 17 on the periodic table; they have seven outer electrons and are very reactive. 10. Ion – charged particles formed by the transfer of electrons from one element or combination of elements to another element or combination of elements. 11. Multimeter – device for measuring current, voltage and resistance. 12. Neutron – neutral particle found in the nucleus of an atom. 13. Noble gas – Group 18 on the periodic table; their outer orbital is full and are therefore nonreactive. 14. Nucleus – the center of the atom that contains neutrons and protons and is positively charged. 15. Orbital – the area surrounding the nucleus where electrons with a certain energy are likely to be found. 16. Period – elements going across the periodic table. 17. Physical properties – characteristics that do not involve substances changing into other substances, such as density, boiling point, melting point, freezing point, conductivity and color. 18. Proton – positively charged particle found in the nucleus of an atom. 19. Reactivity – the rate at which chemical substances tend to undergo chemical reactions through time. 20. Transition metal – the elements in the middle of the periodic table. 21. Valence electron - the electrons that bond to another atom.

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GK12 Module Student’s Guide

Periodicity of the Periodic Table Background: The set up for this experiment is as follows: there is a solution with a certain compound, and there is a current that is run through the solution that separates the compound into its elements. When these elements separate, they have a charge. We are going to figure out what that charge is. 1. Na(NO3)1 What is the sodium ion’s charge? If this compound is chemically neutral, then can you figure out what the nitrate ion’s charge is?

2. Ca(NO3)2 What is the calcium ion’s charge? What is the nitrate ion’s charge?

3. Fe(NO3)3 Can you guess what the iron ion’s charge could be? What about the nitrate ion’s charge? Helpful information:     The battery is what breaks the compound apart into its elements. The elements are charged, and they are what keep the current running. We are going to measure the current of the ions using a multimeter. We are going to measure everything in Amps, which is the unit for electrical current.

Something to note: water by itself has no charge. If we were to hook this experiment up to pure water, the multimeter would read 0 Amps. Problem (What are you trying to test and understand?): How does the charge of an element affect current?

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GK12 Module Student’s Guide

Materials:  Na(NO3)1  Ca(NO3)2  Fe(NO3)3  Wire with alligator clips attached to each end (2 wires, 4 clips)  A block of wood with two nails (2.5inches long) that are 1cm apart  Multimeter  6V Battery  150mL beaker (3)  Rinse bottle  Kimwipes  Waste beaker  Scoopula/spoon  Deionized water Procedure: 1. Connect one of the alligator clips to the positive end of the battery and connect the other alligator clip to one of the nails. Take the other wire and connect one alligator clip to the negative end of the battery and the other alligator clip to the red wire of the multimeter. 2. Place the sodium nitrate solution into a beaker. 3. Put the block of wood on top of the beaker and make sure the nails are in the water. 4. Hypothesis 1: Record in your lab report what you think will happen when we put the sodium nitrate in water and hook it up to the battery and multimeter. Why do you think this?

5. Turn the multimeter on to the side that says Amps, and then take the black wire and touch the metal end to the top of the empty nail. If the multimeter reads a negative number, then switch the red and black wires. 6. Make a chart that has the element name and Amps. Write down the amount of current in Amps.

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GK12 Module Student’s Guide

7. Hypothesis 2: Record in your lab report what you think will happen when we put the calcium nitrate in water and hook it up to the battery and multimeter. Why do you think this?

8. Repeat this process for calcium nitrate, and write down the amount of current in Amps. 9. Hypothesis 3: Record in your lab report what you think will happen when we put the ferric nitrate in water and hook it up to the battery and multimeter. Why do you think this?

10. Repeat this process for ferric nitrate, and write down the amount of current in Amps. Observations: 1. Make a chart with the amount of Amps that each compound produced.

2. Draw a picture of the experiment and label the positive and negative ends of
the battery and the electrode that Ca, Na, Fe and NO3 are attracted to.

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GK12 Module Student’s Guide

Conclusions: 1. Make a bar graph showing the compound and the number of Amps produced.

2. What can you conclude about the relationship between the charge of an element and the current that is produced?

3. Does this support or disprove each of your hypotheses? Why?

4. How might this be used to identify an element or its place on the periodic table?

5. How might this have been useful for creating the periodic table of elements?

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