Common Groups of Elements

Students need to understand not only what the different properties of elements are, but also how those properties help to organize the periodic table to support their success with the two Performance Expectations (PEs) HS-PS1-1 and HS-PS1-2.  HS-PS1-1 asks students to be able to predict element properties based on electron structure and element position on the periodic table.  HS-PS1-2 asks students to explain simple chemical reactions based on valence electrons and periodic table trends.  Students are far more successful in understanding both of these PEs with a foundation in understanding elemental families.

In order for students to "discover" (with guidance, of course) the different crucial properties that determine how elements are grouped and organized on the periodic table, I give each student an element identity.  Students then go through a process of comparing and contrasting their elements with other students in class.  As they do so, the differences and similarities should become apparent and students use the information on their individual element cards to begin developing a way to "group" similar elements.

Finally, students will compare their element with the rest of the classes' elements to group into "families" of their own creation.  

While I take attendance, students do a warm-up activity in their composition Warm-Up/Reflection books.  I use this warm-up to probe for students' prior knowledge about the day's upcoming lesson.  (To read more about Warm Up and Reflection Books please see the attached resources.)  For this particular lesson, my intention is to be as open-ended as possible.

Today's Warm-Up: "How do you sort things?"

In this case, the warm-up is asking students to apply prior knowledge and prepares them for today's activity during which they are expected to compare and contrast different elements. 

If time permits, I walk around with a self-inking stamp to stamp the completed warm-ups indicating participation, but not necessarily accuracy.  On days when there is too much business keeping, I do not stamp.  Students have been told that warm-ups are occasionally immediately checked and other times not.  At the end of each unit, Warm-Up/Reflection Books are collected and spot-checked.  

Today, I do not stamp--instead I ask students to share out answers.  As students share out, I list on the white board their answers.  Some common answers include:

• Size or shape
• Color
• Use or function
• Age
• Sex
• Good or bad
• Who they belong to

I leave the answers on the board to prompt continued thinking about what other possible answers might be while students embark on the day's activity.

As I walk around to stamp student warm-ups, I hand out pre-cut cards of elements.  The element cards can be found here: Element Groups Properties Cards.  Depending on the level of my students, I might print out the cards on different colored cardstock (one color per different page in the file--there are seven pages).  If my students are an honors class or high level performers, I use the same color for everybody.  If not, I print out each page on a different color paper or cardstock to serve as a not-so-subtle visual hint for how to finally sort the elements into families.

Once every student has an element card, I ask students to read the card and tell me what types of things are listed on the card.  I expect students to notice that these things are included:

• number of protons
• number of neutrons (which some elements may have multiples listed)
• number of electrons
• atomic number
• atomic mass
• number of valence electrons (students may not even know what these are)
• how many electrons each element tends to gain or lose (or both)
• a few additional properties (that should help students sort into element families later--but I don't tell them that!)

I direct students to take out a clean sheet of paper and put the appropriate heading at the top.  I tell students to write their element at the top as a title.  Then, I show students how to make a T-chart on their papers (I use a whiteboard, but a document camera and projector could also be used.).  The table should have as two column headings "Similarities" and "Differences."

I tell students to pair up.  If there is an odd number of students, I let one trio exist instead of a pair.   Students should list the element of their partner at the top of the T-chart.  They will have 3 minutes to find similarities and differences between the elements.  And then they will need to find a new partner and repeat the comparing/contrasting twice.

At the end of 10 minutes, students should have completed 3 different T-charts on their papers.

Here are samples of some students' t-charts as they are working: Comparing Element Properties 1 and Comparing Element Properties 2.

And here are samples of completed products: Common Element Families 3 T-Charts and Common Element Families 3 T-Charts 2.

Now that students have had a chance to compare and contrast their elements with three others, students should have a better idea about how to compare and contrast elements when trying to group like elements together.  

I instruct students to think about how we might sort elements.  I ask students:

• How would you want to group elements? (group like elements together)
• How do we know elements are "alike"?(they act the same)
• How would you tell based on the information on the cards?  (behavioral properties are listed on the bottom)
• What properties might we compare to find elements that behave similarly?  (students may or may not know about how valence electrons affect reactivity, but most will see that the number of valence electrons indicates how many electrons will be gained/lost in many cases)

Every student will need to find a "family."  I will encourage students to get up and move around before settling in at a lab station with their determined family.  If students are having difficulty finding the proper family, I might ask some of the following questions to get students on the right track:

• What properties are listed on the bottom of the card?  Can you find other elements that behave the same way?
• How many valence electrons does your element have?  Does that relate to any shared properties between different elements?
• Does your element tend to gain or lose electrons?  Can you find other elements that match?

Once students feel they have found their elemental families, I will ask students to answer the following questions on a piece of chart paper (by writing the questions on the whiteboard):

1. What properties are required to be a member of your family?
2. What elements have you decided are members so far?
3. Are there any differences between your family members?

Students will share out their answers to the entire class, presenting as a group using the chart paper.

Key learning that needs to take place is:

• Elements can be grouped based on their properties.
• There is a correlation between element properties and tendency to gain or lose electrons.
• There is a relationship between the number of valence electrons and how many electrons elements tend to gain or lose.

I ask the following questions as we are discussing the chart papers to ensure students are making those critical connections:

• What else did your elements have in common? (Tendency to gain or lose a specific number of electrons and number of valence electrons in addition to behavioral properties listed at the bottom of the cards are possible answers EXCEPT for the Transition Metal group.)
• How many valence electrons do the elements in your group have? (Answers will vary depending on the specific group--but the follow-up question is what is important.) followed by How many electrons do the elements in your group tend to gain or lose?  Is there a relationship between those two characteristics?  (Students should begin to piece together that the number of valence electrons determines how many electrons elements gain or lose, and that the tendency is to either lose all valence electrons or gain enough to have 8.)