1. Elvis Perkins, a rather shy fellow, is getting on the bus shown at right. Which seat do you think he will probably sit in?

Student Exploration: Electron Configuration

Vocabulary: atomic number, atomic radius, Aufbau principle, chemical family, diagonal rule, electron configuration, Hund’s rule, orbital, Pauli exclusion principle, period, shell, spin, subshell

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

1. Elvis Perkins, a rather shy fellow, is getting on the bus shown at right. Which seat do you think he will probably sit in? 

2. Marta Warren gets on the bus after Elvis. She is tired after a long day at work. Where do you think she will sit?

3. In your experience, do strangers getting on a bus like to sit with other people if there is an empty seat available?

Gizmo Warm-up

Just like passengers getting on a bus, electrons orbit the nuclei of atoms in particular patterns. You will discover these patterns (and how electrons sometimes act like passengers boarding a bus) with the Electron Configuration Gizmo™.

To begin, check that Lithium is selected on the PERIODIC TABLE tab.

1. The atomic number is equal to the number of protons in an atom.

How many protons are in a lithium atom?

2. A neutral atom has the same number of electrons and protons.

How many electrons are in a neutral lithium atom?

3. Select the ELECTRON CONFIGURATION tab. Click twice in the 1s box at upper left and once in the 2s box. Observe the atom model on the right.

What do you see?

Question: How are electrons arranged in elements with atomic numbers 1 through 10? 

1.Infer: Based on its atomic number, how many electrons does a hydrogen atom have?

2.Arrange: The Aufbau principle states that electrons occupy the lowest-energy orbital. Click once in the 1s box to add an electron to the only orbital in the s subshell of the first shell.

Click Check. What is the electron configuration of hydrogen?

3.Arrange: Click Next element to select helium. Add another electron to the 1s orbital. The arrows represent the spin of the electron. What do you notice about the arrows?

The Pauli exclusion principle states that electrons sharing an orbital have opposite spins.

4.Check your work: Click Check. What is the electron configuration of helium?

5.Arrange: Click Next element and create electron configurations for lithium, beryllium, and boron. Click Check to check your work, and then list each configuration below:

6.Arrange: Click Next element to select carbon. Add a second electron to the first 2p orbital.

Click Check. What feedback is given?

7.Rearrange: Hund’s rule states that electrons will occupy an empty orbital when it is available in that subshell. Rearrange the electrons within the 2p subshell and click Check. 

Is the configuration correct now?

Show the correct configuration in the boxes at right:

8.Compare: How are the electrons in the 2p subshell similar to passengers getting on a bus?

9.Practice: In the spaces below, write electron configurations for the next four elements: nitrogen, oxygen, fluorine, and neon. When you are finished, use the Gizmo to check your work. Correct any improper configurations.

10.Apply: Atoms are most stable when their outermost shell is full. If their outermost shell is not full, atoms tend to gain, lose, or share electrons until the shell fills up. While doing this, atoms react and form chemical bonds with other atoms. 

11.Think and discuss: Select the PERIODIC TABLE tab, and look at the second row, or period, of the table. How does this row reflect the subshells of the second shell?

Question: How do the radii of atoms change across a period of the periodic table?  

1.Predict: Positively charged protons in the nucleus of an atom are attracted to negatively charged electrons. 

How do you think the atomic radii will change as electrons are added to a shell?

2.Arrange: Create a proper electron configuration for sodium. After clicking Check, note the Electron configuration and the Atomic radius now listed at right.

Sodium electron configuration:  Atomic radius:

3.Compare: Click Next element, and then add an electron to the magnesium atom. Click check, and record the electron configuration and atomic radius below. 

Magnesium electron configuration:  Atomic radius:

4.Gather data: Create electron configurations for the next six elements. Record the electron configuration and atomic radius of each. (Note: The symbol for picometer is pm.)

5.Analyze: How does the atomic radius change across a period of the periodic table? 

Interpret: Select the ATOMIC RADIUS tab. What do you notice? 

7.Predict: On the ATOMIC RADIUS tab click Clear. Select the PERIODIC TABLE tab. Elements in the same column of the periodic table are called chemical families, or groups. 

How do you think the size of atoms will change from top to bottom within a chemical family?

8.Test: Hydrogen, lithium, and sodium are all in the same chemical family. Use the Gizmo to find the atomic radius of each, and list them below.

9.Analyze: How does the atomic radius change as you go from the top to the bottom of a chemical family?

10.Challenge: Think about the factors that control atomic radius and the patterns you’ve seen.

A.Why does the atomic radius decrease as electrons are added to a shell

B.Why does the atomic radius increase as you go from the top to the bottom of a chemical family? 

11.Think and discuss: Compare the electron configurations of hydrogen, lithium, and sodium. Why do you think these elements are grouped in the same family?

Introduction: Beyond argon, it is a bit tricky to determine which subshell gets filled next. There are several rules that scientists use to determine the electron configurations of larger atoms.

Question: How are the electron configurations of elements beyond argon determined? 

1. Arrange: Create the correct electron configuration for argon. Then, click Next element to get to potassium (K). Click once in the first 3d orbital, and then click Check. What feedback is given

2. Rearrange: As it happens, the 4s subshell is a lower-energy subshell than 3d, so it is filled first. Remove the electron from the 3d orbital and place it in the 4s orbital. Click Check. (Note: For simplicity, all but the outer shell electrons will disappear on the Bohr Model.) Is this configuration correct

3. Arrange: Click Next element and add an electron for calcium. Click Check. What is the electron configuration for calcium?

4. Arrange: Click Next element and add an electron for scandium. Try different orbitals until you find the right one. What is the electron configuration for scandium

5.Observe: Scandium is the first element to contain electrons in the d subshell. How many orbitals does the d subshell have, and how many electrons can fit in the d subshell?

6.Infer: Select the PERIODIC TABLE tab. The middle section of the table is a chemical family called the transition metals. Why do you think this section is ten columns wide?

7.Make a rule: The diagonal rule explains which subshell will be filled next. To follow the diagonal rule, move down along an arrow until you reach the end of the arrow. Then move to the start of the next arrow to the right. 

A. Which subshell is filled after 4p?

B. Which subshell is filled after 6s?

C. Which subshell is filled after 5d?

8.Practice: Determine the electron configurations of the following elements. Use the Gizmo to check your work. (Note: In some cases, the diagonal rule doesn’t work perfectly. If you submit a theoretically correct configuration, the Gizmo will give you the actual configuration.)

9. Infer: Select the PERIODIC TABLE tab. Earlier you saw that the transition metals represent the filling of the d subshells. Now locate the purple lanthanides and actinides on the bottom rows of the periodic table.

A. How many elements are in the in the lanthanides series?

B. Which subshell is represented by the lanthanides family?

C. Which subshell is represented by the actinides family?

D. In general, how is the shape of the periodic table related to electron configurations? (If necessary, continue your answer on another sheet of paper.)