1. 2. 3. what are the trends for atomic radii? why do these trends exist? 4

1. 2.3. What are the trends for atomic radii? Why do these trends exist?4.

Catalyst

Down in Front!

1.9 – I can define and calculate the effective nuclear charge for an atom and explain how this impacts observed periodic trends.

1.10 – I can define atomic/ionic radius and explain how it relates to the effective nuclear charge. Furthermore, I can explain how this trend changes as you move throughout the Periodic Table and relate it to the elements quantum electron configuration.

Today’s Learning Targets

The force felt by two charged objects is directly related to the size of the charge and inversely related to the distance between the charges.

The force on the electron increases as the nuclear charge increases

The force on the electron decreases as the nuclear charge decreases

Coulomb’s Law

Periodic trends depend on how well electrons “feel” the nucleus

The effective nuclear charge (Zef) is the force felt between the nucleus and the electron of interest

Effective Nuclear Charge

In elements with many electrons, inner electrons shield the valence electrons.

This occurs because the core electrons act to shield the valence electrons from the full positive charge of the nucleus.

Electron Shielding

Do you think the Zef increases or decreases as we go down a group the Periodic Table?

What about as we go across a period? Justify your answer with evidence and the

idea of electron shielding.

Predict the Trend

The further away from the nucleus, the less the nuclear charge is “felt”, so Zef decreases down a group.

As you continue across a period, there are no more core electrons, but there is a stronger positive charge

Therefore, as you go across a period Zef increases.

Trends in Zef

Zef decreases

Zef increases

What is the trend for atomic radii as you go throughout the Periodic Table? Justify your response

Quick Write

Atomic radii increase down a group and decrease across a period.

They increase down a group because more orbitals are being added, making the element “bulkier”

The decrease across a period because Zef is increasing, thus causing the electron to be more attracted to the nucleus.

Trends for Atomic Radii

Removing electrons causes the radius to decrease

Removing electrons causes orbitals to be removed and electron-electron repulsions to decrease

Both of these lead to an increase in Zef and a decrease in the ionic radius

Radii of Cations

Adding electrons causes the radius to increase

Adding electrons causes an increase in electron – electron repulsions, so Zef decreases.

A decrease is Zef causes the radius to be larger

Radii of Anions

Arrange Na+, K+, and K in order of increasing atomic radius

Class Example

Arrange the ions K+, Cl-, Ca2+, and S2- in order of decreasing size.

Table Talk

Arrange the following atoms from smallest to largest: Rb+, Sr2+, Y3+

Table Talk

Summarize

Pick a SideI am going to project up numerous

statementsYou must decide whether you agree or

disagree.Be prepared to defend your response!

Pick a Side Questions1. Coulombs Law says that as you pull charges

away from one another, the force increases.2. The effective nuclear describes the

attraction between the nucleus and the electron of interest.

3. Effective nuclear charge decreases down a group because there are more electrons.

4. Effective nuclear charge increases across a period because of the more positive nucleus.

5. The ionic radius is always larger than the atomic radius for a given atom.

Pick a Side Questions (cont.)5. Order the following from smallest to largest radius: Se2-, Te2-, Se

- Answer: Se, Se2-, Te2

6. Order the following from largest to smallest radius: Co3+, Fe2+, Fe3+

- Answer: Co3+, Fe2+, Fe3+

7. The effective nuclear charge has littler overall impact on the atomic and ionic radius of an element

Closing TimePre – Lab for Lab 3 due at the start of lab on

Thursday/FridayFinal lab right up (results and conclusions) due

Monday/Tuesday for Lab 2.To be on track, read sections 7.1 – 7.3 and

answer the corresponding problems