Atoms and Elements

Unit Overview

This unit establishes an important foundation for much of what will follow in Chemistry 20 and 30. Components and characteristics of atoms are considered. An understanding of the structure of the nucleus provides students with the basis for understanding how the average mass number of an element is determined.

This unit offers an opportunity to consider the descriptive chemistry of the elements, an area of chemistry which was deemphasized in the previous chemistry curriculum. It fits well with the discussion of classification of the elements.

Consideration of the properties of some of the elements leads to a discussion of the organization of the periodic table. Patterns in the periodic table are then examined in more detail.

Students gain a historical perspective, recognizing that many conventions that are in use today have been based on the work of previous scientists. This provides them with an important insight into the nature of science.

Factors of scientific literacy which should be emphasized

• A2 ..........historic
• A6 ..........probabilistic
• A7 ..........unique
• A8 ..........tentative
• A9 ..........human/culture related

• B3 ..........orderliness
• B6 ..........symmetry
• B9 ..........reproducibility of results
• B11 ..........predictability
• B13 ..........energy-matter
• B15 ..........model
• B20 ..........theory
• B22 ..........fundamental entities

• C1 ..........classifying
• C8 ..........hypothesizing
• C9 ..........inferring
• C10 ..........predicting
• C13 ..........formulating models
• C15 ..........analyzing
• C20 ..........defining operationally

• D1 ..........science and technology
• D5 ..........public understanding gap
• D7 ..........variable positions

• E3 ..........using equipment safely
• E4 ..........using audio visual aids
• E5 ..........computer interaction
• E11 ..........measuring mass

• F2 ..........questioning
• F3 ..........search for data and their meaning
• F5 ..........respect for logic
• F7 ..........demand for verification

• G3 ..........continuous learner
• G5 ..........avocation
• G6 ..........response preference
• G8 ..........explanation preference
• G9 ..........valuing contributors

Foundational Objectives for Chemistry and the Common Essential Learnings

Discuss the development of ideas about the structure of matter .

• Outline Aristotle's ideas on the nature of matter.
• Explain the contributions of the early alchemists.
• Summarize the contributions made by Dalton, Lavoisier, Berzelius, Thomson, Rutherford, Milliken, Planck, Bohr, de Broglie, Schrödinger or Heisenberg in developing a model of the structure of the atom.
• Understand how theory is used to explain observations.

Identify the relationships among the components of the atom.

• Identify protons, neutrons, and electrons as constituents of atoms.
• Consider the forces which hold the atom together.
• Draw Lewis diagrams to indicate the valence electron structure of atoms.
• Recognize the terminology used to describe atoms and their isotopes: atomic number; nucleon (mass) number; atomic mass; atomic mass unit: average atomic mass.
• Discuss the concept of the mole.
• Distinguish between isotopes of an element.
• Recognize that there is a difference between mass and weight.
• Calculate atomic mass (atomic weight) values when given the percentage of each isotope of an element.

Examine how elements are described and classified.

• Recognize that elements have characteristic properties .
• Classify elements according to their properties.
• Identify some elements by their properties.
• Describe the development of the periodic table by Mendeleev.
• Explain the basic principles of organization of the periodic table.
• Identify trends and patterns within the periodic table.
• Understand the history of the use of symbols for the elements.
• Use symbols for the elements correctly.
• Use the periodic table to determine the valences of elements.
• Compare several forms of the periodic table and recognize that each has its advantages.

Understand and use the vocabulary, structures and forms of expression which characterize chemistry. (COM)

• Incorporate the vocabulary of chemistry into writing and talk about chemistry.
• Recognize the periodic table as a source of information.

Apply knowledge of numbers and their interrelationships. (NUM)

• Read and interpret information about elements from charts and tables.
• Use numerical data to compare and describe elements.

Suggested activities and ideas for research projects

• What chemical elements are of importance to the economy of Saskatchewan? Report, using posters and a short oral presentation, on one of the elements. Include such information as its symbol, electron structure, chemical family (group), chemical and physical properties, in what forms it is usually found in Saskatchewan, and why it is of importance.

• Ask students to design crossword puzzles with the names of elements. The clues would be the symbols for the elements or descriptions of the physical or chemical characteristics of the elements.

• Assign individuals or groups of two or three to prepare reports on one of the elements. Some of the things which might be included in the report are:
  • natural occurrence
  • historic and contemporary uses
  • origin of name
  • when, how, where and by whom it was discovered
  • characteristic physical and chemical properties.

  The report might be presented to the class orally, in a mixed media presentation, on a poster display, as a written report or in some other way.

• Ask each lab group to brainstorm a list of the characteristics of metals. Make sure each group has a recorder who will write down each of the suggestions.

  Then distribute samples of metals in various forms: aluminum foil, copper foil, silver foil (if your budget can afford it), thin zinc and tin sheet, a penny, a nickel, a dime, cobalt pellets or whatever is available. Let the students examine and explore the characteristics of the metals. Compare what they observe with the list of characteristics they created by brainstorming.

  Put two or three groups together and ask them to compare their results. Ask each combined group to list on a poster the characteristics they have discovered. The poster can be presented to the whole class, or displayed on the bulletin board.

• Place a piece of copper foil over a key (or a nickel, quarter or ...) and rub the foil firmly against the key. What is the effect on the foil? Continue rubbing. Does any of the copper transfer to the key?

• Pick up a set of coded toothpicks and a flame test kit with identified chemicals. The flat ends of the toothpicks have been soaked in a salt solution and dried. Your task is to solve the code on the toothpicks. What salt does a red and green stripe represent?

  Note to teachers: To prepare toothpicks for use in this activity, use an elastic band to bundle some toothpicks together, with the flat ends all at the same end of the bundle. Stand the bundle, flat ends down, in about 2 cm of a saturated salt solution. Leave the bundle there overnight. Remove the bundle and allow to dry. Repeat this procedure for as many different salts as you wish.

  Spread the dry toothpicks and code them on the narrow ends using felt tip markers. For example use a single red line to indicate copper chloride, a blue line to indicate copper sulphate and green and yellow bands for copper nitrate. Red and blue might indicate lithium chloride.

  This can also be done with a set of coded spray bottles which the students use to spray a salt solution into the flame of the burner.

• Use a cardboard tube spectroscope to observe the spectra produced by fluorescent tubes, sunlight bouncing off a white wall (don't look directly at the sun), and colours produced when salt solutions are sprayed into burner flames.

  Borrow a spectroscope to observe both blue-white mercury vapour street or yard lights and the orange sodium vapour street of yard lights. Does a full moon produce enough light to create a spectrum in the spectroscope?

  How did Bohr use information from hydrogen spectra to develop his model of the atom?

  Note to teachers: It is possible to have students construct their own spectroscopes using cardboard tubes, poster board and cellophane.

• According to information from the American Gold Institute, 30 grams of gold can be hammered into a gold leaf sheet covering almost 10 m². Assume that the area is exactly 10 m². How many atoms thick would the gold leaf be?

• If you have a large blank wall in your laboratory, consider creating a giant periodic table in the space. It could be the conventional 18 group rectangular table or the class might choose to depict one of the alternative forms. Do some research to find out about all the forms of the periodic table which have been devised. Each lab group could pick one and make a presentation to the class outlining its advantages from these one could be selected for the large project. (Or possibly two could be done if the space is large enough.) (This activity was adapted from CHEM13 NEWS, #198, November 1990, page 3, based on an idea contributed by Denise Gordon of Fort Worth, TX)

• A game to play involves spelling names of elements using only the symbols of elements. For example, silicon (element 14) can be spelled using the symbols for silicon, lithium, cobalt and nitrogen. Once you have found a name, you could then give that to another group in scrambled order: what element can be spelled using the symbols of rubidium, nitrogen, oxygen and calcium? This game could be extended to finding other words that can be spelled with element symbols. What word do you get if you put the symbols for lithium, neon and argon in a row?

  (This activity was adapted from CHEM13 NEWS, #198, November 1990, page 3, based on an idea contributed by Duncan Morrison of Vancouver, B.C.)

• Create element quiz questions. These could be presented in a group as a small research project, or individually, one each day, with a prize or commendations to the person able to find the answer. One source of those questions is from a book The Elements by John Emsley (1989), Oxford University Press. (This activity was adapted from CHEM13 NEWS, #197, October 1990, page 5, based on an idea contributed by Reg Friesen of Waterloo, ON)

• Discuss the two meanings of the term element. It is used to mean both 'non-decomposable substance' and 'type of atom'. The context determines which meaning is intended. Examples of statements in which the usage must be clear are:
  • The element copper has a melting point of 1083°C
  • Most fertilizers contain the element nitrogen.

  In the first statement, element refers to the non-decomposable substance copper. Individual copper atoms do not have melting points. In the second statement, element refers to the type of atom since fertilizers do not contain nitrogen gas, the substance. Make sure that the distinction between the two usages is clear.(This was adapted from an article in CHEM13 NEWS, #197, October 1990, pages 8-9, "Temporary Words for 'Element' Aid Thinking in Molecular Terms" by Jan Hondebrink, Enscede, The Netherlands.)

• This assignment is a creative library research paper on an element. The importance of chemical elements in our lives can be strengthened by making the description of an element part of the production of an imaginative, creative product.

  First, select an element and gather information about its:

  • discovery, including derivation of its name
  • method of preparation and purification
  • chemical and physical properties
  • uses and applications

  Take the information you have gathered and create an adventure story involving the element. Weave into that story the factual information you discovered in your research into the element.

  Use a word processor to produce your story, so that it can be bound into a collection of short stories titled Lives of the Elements. As one of the authors of this book, you will be honoured at a reception announcing the book's release. (This activity was adapted from CHEM13 NEWS, #195, May 1990, page 8, based on an idea contributed by Bekye Dewey, Falls Church VA)

• What if iron didn't exist? What could be used instead of iron? What effect would it have on our society? How might history have been different?

  Pick an element other than iron. Answer the same questions with respect to the element you have picked. (This activity was adapted from CHEM13 NEWS, #192, February 1990, page 3, based on an idea from Michael Kelly, Westford MA and reported by Bruce Hemphill, St. Catharines, ON)

• Chemical bingo is one way to become more familiar with the symbols for the elements. Prepare bingo cards, but in place of the numbers use symbols. (Use regular bingo cards to prepare the cards. Develop a master key of what symbols are used to replace each number on the cards. Each column could be reserved for a particular group of elements e.g., column B could be used for groups I and II elements, column I could represent elements from group VII.)

  Call out the name of an element. In order to mark the space, students must be able to recognize the correct symbol if it appears on the cards. Tables and charts can be used as aids. Set a time limit before calling out the next element, and set rules regarding the use of reference materials.

  Use regular bingo variations such as: full card blackout, roving kite (any four corner squares plus a diagonal), roving L (any two outside lines sharing a common corner, roving T (any outside line with a centre line), 8 around the free (all eight squares around the free square in the centre), wee house (8 around the free, plus the square in the top centre of the top row), etc.

• Design an advertising campaign for an element. Pick an element. Create a fact sheet listing the physical and chemical properties of the element, along with any interesting facts about the element. Then produce a poster with a logo for the element and promoting its use. As a final part of the advertising package, an audio or video taped commercial for the element should be produced.

  Note to the teacher: This project can be evaluated by the students. The students could produce a list of common criteria on which they will base their evaluation. Each package could be given to five students to evaluate. The average mark given by the student graders could form the mark for the project. As a wrap-up, you might show a copy of "The Ball of String" sketch from Monty Python's Flying Circus tv series, in which an advertising campaign to sell bits of string in four inch lengths is devised.

  (This activity was adapted from CHEM13 NEWS, #192, February 1990, page 3, based on an idea from Michael Kelly, Westford MA and reported by Bruce Hemphill, St. Catharines, ON)

• What is the origin of the term 'mole' to describe Avogadro's number of particles?

• Demonstrate atomic spectra as a result of electron transition. You will need a flashlight, red confetti, a lab coat, a sturdy chair and a sturdier table or demonstration desk. Ask the students to gather closely around the table so they can see.

  Put the lab coat on, with the red confetti in one pocket. Ask a student to shine the flashlight on you while you stand on the floor. Explain that you represent the electrons of a whole bunch of hydrogen atoms and the floor is your ground state. Energy input (in this case light from the flashlight because heat from a bunsen burner is too risky!) can cause electrons to become excited and move to higher energy levels.

  Those higher levels are quantized, and you can't be in between them. Step up on the chair and start to move a little to represent the second energy level. Then step up to the table to represent the third energy level and start to do a little dance to represent lots of energy.

  Then mention that electrons can't stay in the excited state indefinitely so they will go back to ground state. Point out the two ways of getting to ground state. Ask what happens to the energy when the electrons go back. Hopefully, someone will say that the energy they absorbed is emitted.

  If not, you say it as you step back down onto the chair, reaching into the pocket containing the red confetti and throwing a handful out over the students' heads. Each piece of confetti represents one photon of light (why is the light monochromatic?) which was the energy emitted by one electron going from energy level three to energy level two.

  Since the electrons have not yet returned to the ground state, ask what will happen when they go down the last step. This time someone should say that energy will be released. As you step back to the floor, reach into an empty lab coat pocket and throw some imaginary confetti on them. This represents invisible ultraviolet light.(This activity was adapted from CHEM13 NEWS, #190, December 1989, page 11, based on an idea contributed by Jerry Sears of Wayne, MI)

• What colour is pure copper? To find out, hang a strip of copper in a 250 mL beaker so that the bottom of the strip comes within 1 cm of the bottom of the beaker. Put methanol or propanone in the beaker to a depth of about 0.5 cm so that the copper is not touching the liquid.

  Remove the copper from the beaker and heat in a burner flame. Make sure the burner is at least 1 m from the beaker, since both methanol and propanone are flammable. If the liquid does catch on fire, gently cover the mouth of the beaker with a notebook. This will smother the fire.

  Bring the red hot copper back to the beaker and suspend it above the liquid. The hot copper should oxidize the vapours of the liquid, thus itself being reduced to pure metallic copper. If it doesn't work the first time reheat the copper. What accounts for the 'copper colour' of copper?

  (This activity was adapted from CHEM13 NEWS, #188, October 1989, page 16. The Journal of Chemical Education (May 1989, page 400) was cited there as the source.)

• Create a wordsearch on a 20 by 20 grid, using the names of elements 1 to 103. Create a 'score' for the wordsearch by adding the atomic numbers of the elements in the puzzle. Who can create a puzzle with the highest score? Bind the puzzles from your class into a book. Copies of the book could be given to a grade six teacher for use with students at that level who are just starting to learn about atoms and elements.

  (This activity was adapted from CHEM13 NEWS, #192, February 1990, page 3, based on an idea from Michael Kelly, Westford MA and reported by Bruce Hemphill, St. Catharines, ON)

• What causes the aurora borealis? Where does the light come from? Do you think Hendrik Lorentz knew how they were produced? Why?

• Select one of the elements from group IA to group VIIIA (or groups 1,2, 13-18). Find out the physical and chemical properties of that element, in what form it is found, how it is extracted or purified and where and how it was discovered. Submit a written report containing what you have found out about your element.

  After the reports have been returned, group yourself with students who have elements which are in the same group (family) of the periodic table. Create a list of common properties and trends in properties among those elements.

  Find a creative way to present this information about your chemical family to the rest of the class. The presentation should last from three to five minutes. Possibilities for reporting are a poster presentation, part of a tv quiz show or talk show, raps, plays, poems, stories, interviews or videos. Also prepare a summary sheet with important information about your family to distribute to everyone in the class.

  Split your family into two groups to do the lab activities assigned by your teacher.

  Note to teachers: Have students select elements by drawing from a hat or some other way which will randomize the groups when they are formed. The lab activities assigned can be any which examine the properties of the elements. Choose these activities from among those listed in this guide or from other sources.

  (This activity was adapted from CHEM13 NEWS, #206, October 1991, page 4, based on an idea contributed by Ken Lyle, Houston, TX)

• How many different forms of the periodic table have been produced? Select one form other than the standard block form which appears in most books. Explain the basis for its structures, as well as identifying the advantages and disadvantages of the form.

• Select an "Element of the Day" to highlight each day. The name of the element could be posted on the blackboard or on a poster. The elements could be selected randomly or according to some pattern. If there is a pattern the students could be challenged to predict tomorrow's element. The presentation of the element for the day could range from simply displaying its name to display of a sample or picture of a sample, its characteristics, its symbol, common reactions it is involved in, where and in what form it is found, and so on.

  The same idea could be used for a "Molecule of the Day".

Sample ideas for evaluation or for encouraging thinking

• Sodium has only one more proton than neon. How are these two elements different? Why are they so different?

• How can there be so many different forms of the periodic table? Why isn't there one, best, most correct table?

• Which elements are called the transitional elements? What transition do they represent or indicate?

• Scientists now believe that the basic components of matter are quarks and leptons. Ideas about matter have come along way since Aristotle was arguing against Democritus's idea of indivisible pieces of matter he called atoms. Are atoms still a useful concept even though we believe that they are not indivisible?

• When an electric spark forces an electron from its ground level, what attractive force must be overcome? What evidence appears when the electron drops back to its starting place? What kind of waves are produced? At what point does the electron have the greatest amount of energy?

• What must be done to a 2 level electron to make it a 3 level electron? What happens when the 3 level electron becomes a 2 level electron?

• Draw the electron dot (Lewis) representation for phosphorus.

• In most chemical reactions involving lithium, the lithium atom loses an electron and forms an ion. On the other hand, fluorine atoms tend to form ions by gaining an electron. Why do these elements behave so differently in the formation of ions?

• Why do metals have low ionization energies?

• Suppose that energy is released during the addition of an electron to a neutral atom. Which is more stable - the atom or the resulting ion?

• What is similar in the electron structure of each of the noble (inert) gases?

• How similar were the ideas of Dalton and Democritus about matter? How were their ideas different?

• What fundamental problem with the Bohr model of the atom did de Broglie, Schrödinger and Heisenberg all tackle?

• What constraint in analyzing the motion of the electron in the atom did Heisenberg uncover?

• How many electrons, protons and neutrons are found in an atom of ¹⁴C (carbon-14)?

• If the main isotopes of chlorine are ³⁵Cl and ³⁷Cl, how does the average atomic mass come to be 35.5 amu?

• What is the relationship between ¹²C, atomic mass units and the mole?

• What are the isotopes of uranium? Which one is most important to Saskatchewan's economy?

• Find the element with the following characteristics:
  • silvery white metal
  • fifth most common element
  • can be replaced in its most common nutritional source by a radioactive isotope of strontium
  • important component of the structure of human bone

  Make up some more of these to share with your classmates.

• What is a major source of radioactive strontium ions in the environment?

• What properties do all halogens have in common?

• What do elements found in groups IIA and IIB (or groups 2 and 11) have in common?

• Using the ionization energies for all members of period 2 of the periodic table, draw a line graph showing the relationship between atomic number and ionization energy? Which is the dependent variable in these data?

  Predict the shape of the line graph for the ionization energies of the period 3 elements plotted against the atomic numbers? How about for period 4?

• How is a decomposition reaction different from a synthesis reaction?

• Can an element be decomposed in a chemical reaction? Is ozone an element? Discuss the differences between elements and the atoms they are composed of.

• Silicon is sometimes called a metalloid. It is also described as a semiconductor. Why does it not fall into the class of either metals or nonmetals? Are there other elements which are similar to silicon in this respect? Are all members of Group IVA (group 14) also semiconducting metalloids?

• What tests could be done to determine if a piece of solid was metallic?

• The most common element in the earth's crust is oxygen. Why isn't this oxygen available for breathing?

• Aluminum is the third most common element in the earth's crust. Over 8% of the crust is aluminum. Yet bauxite, the ore from which aluminum metal is refined is quite rare. Why?

• Clues to the Greek and Latin roots of the names of elements are given in the statements below. Try to identify the elements for each group of clues.
  • Some elements are named for a colour. Which elements correspond to greenish-yellow, rose, violet, indigo, deepest red, sky blue, the rainbow, and colour itself.
  • These have Scandinavian origins: a goddess; a god of war; a heavy stone; the earliest name for Scandinavia.
  • Which elements have names arising from "liquid silver", a magnet, a green twig, a stone, flint, and a smell?

  (This was adapted from CHEM13 NEWS, #182, January 1989, page 10, based on an article contributed by R.J. Friesen, Waterloo, ON.)