Effective Nuclear Charge and Atomic Radius

AP Periodic Trends Day 2

by Andrew Baldwin

​Objectives

​Explain the relationship between trends in atomic properties of elements and electronic structure and periodicity.

• ​The organization of the of the PTE is based on the recurring properties and explained by the pattern of electron configurations and the presence of completely or partially filled energy shells.

• ​The trend in atomic properties within the periodic table (periodicity) can be qualitatively understood through the position of the element in the PTE, Coulomb's law, the shell model, and the concept of shielding/effective nuclear charge. These include Ionization energy, atomic and ionic radii, Electron affinity, Electronegativity.

• ​Periodicity is useful when predicting/estimating values of properties in the absence of data.

Poll

Rate your confidence from yesterday's Lesson. (Think of his name)

Multiple Choice

Looking at atoms in the same group/family, what factor affects Coulombic attraction?

• number of protons

• distance from the nucleus

Multiple Choice

Looking at atoms in the same valence energy level, what factor affects Coulombic attraction?

• number of protons

• distance from the nucleus

Multiple Choice

Ionization energy is the...

• the energy needed to remove an electron from an atom

• ability of an atom to attract electrons from another atom.

Multiple Choice

Electronegativity is the...

• energy needed to remove the outermost electron.

• ability of an atom to attract electrons from another atom.

Multiple Choice

Atomic Radius is...

• The size of the atom from the nucleus to the valence shell

• The amount of energy to remove an electron from the atom.

Multiple Choice

Electron Affinity is...

• the amount of energy released when an electron is added to an atom's valence shell.

• the level of attraction between two atoms when bonded.

Multiple Choice

As the Coulombic attraction increases the atomic radius: increases or decreases?

• increases

• decreases

Multiple Choice

As the Coulombic attraction of an atom increases, the electronegativity of the atom: increases or decreases?

• increases 

• decreases

Multiple Choice

As the Coulombic attractions in an atom decreases, the ionization energy increases or decreases?

• Increases

• Decreases

​How does this work?

When starting a question on periodic trends, we need to consider two things:

• ​the location of the elements

  • ​Same period or same group

• ​Which of the two factors of Coulomb's Law to focus on

  • ​Distance from the nucleus or size of the nucleus

Multiple Choice

Example 1: Calcium has a larger atomic radius than Titanium. Explain the observation.

Are these two elements in the same period (row) or the same group (column)?

• Same Period

• Same group

Multiple Choice

Example 1: Calcium has a larger atomic radius than Titanium. Explain the observation.

Which would cause the observation according to Coulomb's Law?

• Effective Nuclear Charge (Amount of protons in the nucleus)

• Amount of shielding (Energy shells between the nucleus and valence shell)

Open Ended

Example 1: Calcium has a larger atomic radius than Titanium. Explain the observation.

Using the information from the previous two questions to explain the observation.

Multiple Choice

Example 2: Bromine has a smaller electronegativity than Fluorine? Explain the observation based on Coulomb's Law.

Are these elements in the same period (row) or the same group (column)?

• Same group

• Same period

Multiple Choice

Example 2: Bromine has a smaller electronegativity than Fluorine? Explain the observation based on Coulomb's Law.

Which factor is responsible for the observation?

• Amount of Shielding

• Effective Nuclear charge

Open Ended

Example 2: Bromine has a smaller electronegativity than Fluorine? Explain the observation based on Coulomb's Law.

Use your answers from the previous questions to explain the observation.

Multiple Choice

Which element has the greatest electron affinity: Aluminum (Al)  or Chlorine (Cl)?

• Aluminum (Al)

• Chlorine (Cl)

Multiple Choice

Which element has the greatest ionization energy: Nitrogen (N) or Arsenic (As)?

• Nitrogen (N)

• Arsenic (As)

AP Practice Questions​

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Multiple Choice

Which of the following best helps explain why the electronegativity of Cl is less than that of F?

• The mass of the Cl atom is greater than the mass of the F atom.

• The Cl nucleus contains more protons than the F nucleus

• When Cl and F form bonds with other atoms, the Cl bonding electrons are more shielded from the positive Cl nucleus than the F bonding electrons. 

• Because Cl is larger than F, the repulsions among the electrons in the valence shell of Cl are less than the repulsions among the valence shell of F.

Open Ended

Using the data provided in the image, Predict whether the atomic radius of Magnesium (Mg) will be larger, smaller, or the same as the atomic radius of Sodium (Na).  Explain using principles of Atomic structure and Coulomb's Law.

Poll

Rate your confidence from yesterday's Lesson. (Think of his name)