Name Date Class

Periodic Trends in the Periodic Table

The periodic table organizes elements into related groups. Within these groups, trends in common properties occur. These trends may be used to predict unknown property values for other elements in the same group. In this activity, you will predict properties of elements in the periodic table based on periodic trends.

Problem

How accurately can properties be predicted using trend information in the periodic table?

Objectives

  1. Identify trends among elements in the same group
  2. Draw conclusions about the accuracy of predicting chemical properties using group trends.

Materials

20 index cards, each with property information for one of the first 20 elements. The property information, at a minimum, should include melting point, ionization energy, and electronegativity.

Reference material with experimental values for melting point, ionization energy, and electronegativity for elements 31–36.

Pre-Lab

  1. What periodic trends exist for ionization energy?
  2. What periodic trends exist for electronegativity?
  3. Read over the entire laboratory activity. Hypothesize which method you expect to be the best in confirming the known properties of Ca and K. The worst? Hypothesize which method you expect to be the best in predicting the properties of elements 31–36. Record your hypothesis on page 46.

Procedure

  1. Arrange the index cards for the elements in each group in order of increasing period.
  2. Predict the properties of K and Ca using Method 1. Record your results in Data Table 1.
  3. Predict the properties of K and Ca using Method 2. Record your results in Data Table 2.
  4. Using a suitable reference, such as your textbook, record the known values for K and Ca in Data Table 3. Also record the predicted values for K and Ca from Data Table 1 and Data Table 2 in Data Table 3. Compare the accuracy of Method 1 and Method 2 for predicting the properties of K and Ca. Identify the best method to use for predicting each property.
  5. Use the best predictive method (1 or 2) for each property to predict the properties of elements 31–36 in groups 3A–7A. Record the predicted values in Data Table 4.
  6. Using a suitable reference, such as your textbook, locate the known value for the indicated property and record it in Data Table 4.

Method 1: Using element row in the periodic table

Complete the following steps using elements in the same group as potassium. The term property value refers to the melting point, ionization energy, or electronegativity of the element. Record your results in Data Table 1.

1a. Scale the value of the property of the element in row 3 of the periodic table by multiplying the value by 1.35.

1b. Scale the value of the property of the element in row 2 of the periodic table by multiplying the value by 0.35.

1c. Predict the value of the property of the element in row 4 by subtracting the scaled value of the element in row 2 from the scaled value of the element in row 3.(1c = 1a – 1b) (This is the predicted property value using the atomic mass proportions method.)

1d. Repeat steps 1a through 1e until you have predicted values for the melting point, ionization energy, and electronegativity.

1e. Repeat steps 1a through 1f using elements in the same group as calcium.

Method 2: Using atomic number proportions

Complete the following steps using elements in the same group as potassium. The term property value refers to the melting point, ionization energy, or electronegativity of the element. Record your results in Data Table 2.

2a. Subtract the atomic number of the element in period 2 from the element in period 3.

2b. Subtract the property value of the element in period 2 from the element in period 3

2c. Subtract the atomic number of the element in period 3 from the element in period 4.

2d. Multiply the value found in step 2b by the value in step 2c and divide by the value in step 2a.

2e. Add the value derived in step 2d to the property value of the element in period 3. (This is the predicted property value using the atomic number method.)

2f. Repeat steps 2a through 2e until you have predicted values for the melting point, ionization energy, and electronegativity.

2g. Repeat steps 2a through 2f using elements in the same group as calcium.

Hypothesis



Data and Observations

Data Table 1 (Method 1)
  Melting point Ionization energy Electro-negativity Melting point Ionization energy Electro-negativity
  Potassium (K) Calcium (Ca)
1a. property valueperiod 3 element × 1.35            
1b. property valueperiod 2 element × 0.35            
1c. predicted property value = property valuestep 1a − property valuestep 1b            


Data Table 2 (Method 2)
  Melting point Ionization energy Electro-negativity Melting point Ionization energy Electro-negativity
  Potassium (K) Calcium (Ca)
2a. atomic numberperiod 3 element − atomic numberperiod 2 element            
2b. property valueperiod 3 element − property valueperiod 2 element            
2c. atomic numberperiod 4 element − atomic numberperiod 3 element            
2d. (valuestep 2b × valuestep 2c)/valuestep 2a            
2e. predicted property value = property valueperiod 3 element+ valuestep 2d            


Data Table 3: Identifying the Best Method for Each Property
  Melting point (°C) Ionization energy (kcal/mol) Electronegativity
  K Ca K Ca K Ca
Method 1 value            
Method 2 value            
Known value            
Best method      


Data Table 4: Predicting Property Values for Period 4 Group 3A–7A Elements
Atomic number Property Best method used Calculated value Known value
31 Ionization energy      
Electronegativity      
Melting point      
32 Ionization energy      
Electronegativity      
Melting point      
33 Ionization energy      
Electronegativity      
Melting point      
34 Ionization energy      
Electronegativity      
Melting point      
35 Ionization energy      
Electronegativity      
Melting point      
36 Ionization energy      
Electronegativity      
Melting point      

Analyze and Conclude

  1. Comparing and Contrasting Which method is best for predicting melting point for groups 1 and 2?


  2. Comparing and Contrasting Which method appears to be best for predicting ionization potential for groups 1 and 2?


  3. Comparing and Contrasting Which method appears to be best for predicting electronegativity for groups 1 and 2?


  4. Thinking Critically What may be the cause of the inaccuracies observed?



  5. Thinking Critically After completing the predictions for elements 31 through 36, which method do you believe is better over multiple groups? Explain.




  6. Thinking Critically Do you think simple models can be used to accurately predict unknown element properties?


  7. Error Analysis In the Pre-Lab hypothesis, did you select the best method for predicting the properties of Ca and K? Did you select the best method for predicting the properties of elements 31 to 36? Did a single method work best for all cases?




Real-World Chemistry

  1. In 1960, there were 102 known elements in the periodic table. Since 1960, a significant amount of nuclear research has been done. As of 1997, there were 112 elements in the periodic table. What do you suspect caused the increase in the number of elements?
  2. What unique property of elements 103 and greater would be most useful in placing them in the correct position in the periodic table?