Scientific Understanding

**What sections should I know before attempting to learn this section?**

**What are complete electrons configurations?**

**VIDEO Explanation of complete electron configurations.**

Electron configurations are a map of the how the electrons fill up the different orbitals in order. The electron configurations break into 3 different symbols that each have their own meaning. One example is below:

3p^{5}

The first notation, the number 3, stands for the energy level. The second notation, the letter P, stands for the orbital type. The third and final notation, the exponent or superscript 5, stands for how many electrons are currently filling up those orbitals. The purpose of the questions about the complete electron configurations is for you become familiar with which energy levels and orbitals are closest to the nucleus and thus fill up with electrons first. It is one way to represent where the electrons are in a single atom and can help you predict how bonds form between that atom and other atoms. The complete electron configurations can be related to the periodic table by showing the energy levels and orbitals like on this link. If this is still confusing, there is another way to visualize the electron configurations according to the energy level diagram that I showed earlier in the previous section of energy levels. I will explain how to solve complete electron configuration questions by focusing on how to relate them to the periodic table because I think that is a far easier and better method to learn.

**Examples**: Give the complete electron configurations for the following pure elements. Use the orbital periodic table.

Li | 1s^{2}2s^{1} |

P | 1s^{2}2s^{2}2p^{6}3s^{2}3p^{3} |

Br | 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{5} |

O^{2-} |
1s^{2}2s^{2}2p^{6} |

**VIDEO Complete Electron Configurations Demonstrated Example 1****:** What is the complete electron configuration of Ti? (Solve while allowing your finger to follow along on the periodic table orbitals) Write down each piece of information you learn in order, as you go. You may also need a regular periodic table for reference of where each element is.

**Step 1:**

Where do you start the problem?

Answer: open up the link to the periodic table orbitals and place your eye or finger at the first element (hydrogen).

**Step ****2****:**

What energy level are you at on the periodic table with that first element (hydrogen)?

Answer: 1

What should be written down so far: 1

**Step ****3****:**

What orbital type is the first element (hydrogen) in?

Answer: s

What should be written down so far: 1s

**Step ****4****:**

Count the boxes across the S orbitals until you reach the end. That should represent the number of electrons. How many boxes did you count?

Answer: 2

What should be written down so far: 1s^{2}

**Step ****5****:**

Move to the next orbitals on the periodic table on the periodic table (the next row in this case). What element do you start at if you do?

Answer: Li

What should be written down so far: 1s^{2}

**Step ****6****:**

What energy level is lithium at?

Answer: 2

What should be written down so far: 1s^{2}2

**Step ****7****:**

What orbital type is lithium at?

Answer: s

What should be written down so far: 1s^{2}2s

**Step ****8****:**

Count the boxes across the S orbitals until you reach the end. That should represent the number of electrons. How many boxes did you count?

Answer: 2

What should be written down so far: 1s^{2}2s^{2}

**Step ****9****:**

Move to the next orbitals on the periodic table. What element do you start at if you do?

Answer: B

What should be written down so far: 1s^{2}2s^{2}

**Step ****10****:**

What energy level is Boron at?

Answer: 2

What should be written down so far: 1s^{2}2s^{2}2

**Step ****11****:**

What orbital type is Boron at?

Answer: p

What should be written down so far: 1s^{2}2s^{2}2p

**Step ****12****:**

Count the boxes across the P orbitals until you reach the end. That should represent the number of electrons. How many boxes did you count?

Answer: 6

What should be written down so far: 1s^{2}2s^{2}2p^{6}

**Step ****1****3****:**

Move to the next orbitals on the periodic table (the next row in this case). What element do you start at if you do?

Answer: Na

What should be written down so far: 1s^{2}2s^{2}2p^{6}

**Step ****1****4****:**

What energy level is Sodium at?

Answer: 3

What should be written down so far: 1s^{2}2s^{2}2p^{6}3

**Step ****1****5****:**

What orbital type is Sodium at?

Answer: s

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s

**Step ****1****6****:**

Count the boxes across the S orbitals until you reach the end. That should represent the number of electrons. How many boxes did you count?

Answer: 2

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s^{2}

**Step ****1****7****:**

Move to the next orbitals on the periodic table. What element do you start at if you do?

Answer: Al

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s^{2}

**Step ****1****8****:**

What energy level is Aluminum at?

Answer: 3

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s^{2}3

**Step ****1****9****:**

What orbital type is Aluminum at?

Answer: p

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s^{2}3p

**Step ****20****:**

Count the boxes across the P orbitals until you reach the end. That should represent the number of electrons. How many boxes did you count?

Answer: 6

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}

**Step ****21****:**

Move to the next orbitals on the periodic table (the next row in this case). What element do you start at if you do?

Answer: K

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}

**Step ****22****:**

What energy level is Potassium at?

Answer: 4

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4

**Step ****23****:**

What orbital type is Potassium at?

Answer: s

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s

**Step ****24****:**

Answer: 2

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}

**Step ****25****:**

Move to the next orbitals on the periodic table. What element do you start at if you do?

Answer: Sc

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}

**Step ****26****:**

What energy level is Scandium at?

Answer: 3

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3

**Step ****27****:**

What orbital type is Scandium at?

Answer: d

What should be written down so far: 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d

**Step ****28****:**

Count the boxes across the D orbitals until you reach TITANIUM. That should represent the number of electrons. How many boxes did you count?

Answer: 2

COMPLETE ANSWER: 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{2}

It is also possible to determine the electron configurations of charged elements. What you have to take into account for charged elements is that they will have gained or lost electrons to look like the electron configuration of another element on the periodic table. Another way to phrase this is that the charged element is isoelectric with another element.

**VIDEO Complete Electron Configurations Demonstrated Example 2****:** What is the complete electron configuration of Al^{3+}? (Solve while allowing your finger to follow along on the periodic table orbitals) Write down each piece of information you learn in order, as you go. You may also need a regular periodic table for reference of where each element is.

**Step 1:**

Al^{3+} has electrons that look like what element on the periodic table?

Answer: Count back on the periodic table 3 spaces. It is Ne

Therefore we now look for the electron configuration of Ne.

**Step ****2****:**

What energy level are you at on the periodic table with that first element (hydrogen)?

Answer: 1

What should be written down so far: 1

**Step ****3****:**

What orbital type is the first element (hydrogen) in?

Answer: s

What should be written down so far: 1s

**Step ****4****:**

Answer: 2

What should be written down so far: 1s^{2}

**Step ****5****:**

Move to the next orbitals on the periodic table on the periodic table (the next row in this case). What element do you start at if you do?

Answer: Li

What should be written down so far: 1s^{2}

**Step ****6****:**

What energy level is lithium at?

Answer: 2

What should be written down so far: 1s^{2}2

**Step ****7****:**

What orbital type is lithium at?

Answer: s

What should be written down so far: 1s^{2}2s

**Step ****8****:**

Answer: 2

What should be written down so far: 1s^{2}2s^{2}

**Step ****9****:**

Move to the next orbitals on the periodic table. What element do you start at if you do?

Answer: B

What should be written down so far: 1s^{2}2s^{2}

**Step ****10****:**

What energy level is Boron at?

Answer: 2

What should be written down so far: 1s^{2}2s^{2}2

**Step ****11****:**

What orbital type is Boron at?

Answer: p

What should be written down so far: 1s^{2}2s^{2}2p

**Step ****12****:**

Count the boxes across the P orbitals until you reach NEON. That should represent the number of electrons. How many boxes did you count?

Answer: 6

COMPLETE ANSWER: Al^{3+} = 1s^{2}2s^{2}2p^{6}

**PRACTICE PROBLEMS**: Give the complete electron configurations of the following elements or charged atoms below. Use this periodic table if possible. If that does not work for you try the orbital periodic table.

Mg | 1s^{2}2s^{2}2p^{6}3s^{2} |

As | 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}s^{2}3d^{10}4p^{3} |

Zn | 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10} |

Nd | 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}s^{2}3d^{10}4p^{3}5s^{2}4d^{10}5p^{6}6s^{2}4f^{4} |

Sn^{2+} |
1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}s^{2}3d^{10}4p^{3}5s^{2}4d^{10} |

Rb | 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}s^{2}3d^{10}4p^{3}5s^{1} |

S^{2-} |
1s^{2}2s^{2}2p^{6}3s^{2}3p^{6} |