Sparks CH301 EFFECTIVE NUCLEAR CHARGE AND PERIODIC TRENDS Why is - - PowerPoint PPT Presentation

Sparks CH301

EFFECTIVE NUCLEAR CHARGE AND PERIODIC TRENDS Why is strontium so dangerous? UNIT 2 Day 5

How many electrons in Na have l=0?

QUIZ QUESTION: INDIVIDUAL WORK, NO TALKING

What are we going to learn today?

−Effective Nuclear Charge and Periodic Trends

• Determine trends in effective nuclear charge in the

periodic table

• Relate effective nuclear charge to atomic radii, ionic

radii, and ionization energy

Do all electrons in an atom feel the same attraction to the nucleus?

• A. Yes
• B. No – the ones in lower energy levels feel a

stronger attraction to the nucleus.

• C. No – the ones in higher energy levels feel a

stronger attraction to the nucleus.

POLLING QUESTION

EXAMPLE OF EFFECTIVE NUCLEAR CHARGE

• Consider Li: 1s2 2s1.
• The core [He] electrons shields the 2s electron.

– It does not ‘feel’ the effect of all 3 protons in the nucleus.

As you move across a row (left to right), what happens to Zeff?

• A. It stays the same.
• B. It gets larger.
• C. It gets smaller.

POLLING QUESTION

Shielding and effective nuclear charge

Neon Sodium

Shielding and effective nuclear charge Because of shielding Na is more like H than Ne

As I go from left to right in a period I add electrons: more shielding and I add more protons: bigger Z Which has a larger effect? A) Adding more electrons across period B) Adding more protons across period

POLL: CLICKER QUESTION

• We can use Zeff to determine trends in:

– Atomic radii – Ionic radii – Ionization energy

• Class Activity Handout

• Which would you expect to have the larger

atomic radius: Li or K?

• A. Li
• B. K
• C. They would have equal atomic radii.

QUIZ: CLICKER QUESTION

• Which would you expect to have the larger

atomic radius: C or O? (Consider all you know about the electronic structure of atoms: principle quantum number, effective nuclear charge, etc.)

• A. C
• B. O
• C. They would have equal atomic radii.

QUIZ: CLICKER QUESTION

Figure 12.38: Atomic radii (in picometers)

14

Ionic Radius

Cations are always _______ their respective neutral atoms. Why?

• A. smaller than
• B. the same size as
• C. larger than

POLL: CLICKER QUESTION

Li

Li+ Na Na+

r = 1.52 A r = 0.90 A r = 1.86 A r = 1.16 A

Anions are always _______ their respective neutral atoms. Why?

• A. smaller than
• B. the same size as
• C. larger than

QUIZ: CLICKER QUESTION

F-

F Cl- Cl

r = 0.72 A r = 1.19 A r = 1.00 A r = 1.67 A

Which would have a larger radius: Na+ or Mg2+?

• A. Na+
• B. Mg2+
• C. They would have the same radius.

QUIZ: CLICKER QUESTION

• The three ions, N3-, O2-, and F- have these

three ionic radii (in no particular order): 1.71 A, 1.19 A, and 1.26 A. Which of these three values would be the radius for N3-?

• A. 1.71 A
• B. 1.19 A
• C. 1.26 A

POLL: CLICKER QUESTION

Arrange these elements based on their increasing ionic radii: S, K, Cl

• A. Cl1- < S2- < K+
• B. K+ < Cl1- < S2-
• C. S2- < Cl1- < K+
• D. K+ < S2- < Cl1-

QUIZ: CLICKER QUESTION

Ionic Radius

IONIZATION ENERGY

Which is always higher: IE2 or IE1. Why?

• A. IE2
• B. IE1

POLL: CLICKER QUESTION

As you move across a period, you would expect IE1 to __________. Why?

• A. increase
• B. decrease

QUIZ: CLICKER QUESTION

Thought Question!

As you move down a group, you would expect IE1 to __________. Why?

• A. increase
• B. decrease

QUIZ: CLICKER QUESTION

What have we learned?

LIGHT CAN BE USED TO PROBE THE ENERGY OF ELECTRONS IN MATTER ELECTRONS IN ATOMS HAVE DISCRETE ENERGIES ELECTRONS CAN BE DESCRIBED BY WAVE FUNCTIONS THAT CAN BE CLASSIFIED BY QUANTUM NUMBERS THE HYDROGEN WAVEFUNCTIONS CAN APPROXIMATE THE WAVEFUNCTIONS OF MULTIELECTRON ATOMS THE ORDERING OF ENERGY LEVELS IS GENERALLY THE SAME FOR ATOMS FOR ALL ELEMENTS NUCLEAR CHARGE FELT BY VALENCE ELECTRONS IS SHIELDED BY THE CORE ELECTRONS

Learning Outcomes

Describe the difference between one electron systems and multi-electron systems. Predict electron configurations based on position on periodic table. Apply the Aufbau principle to determine the configuration for any atom or ion. Use Hund’s Rule to determine electron configuration using an

• rbital diagram (electrons in individual orbitals with spins.

Students will use the shell model of multi-electron atoms to describe the concept of core vs. valence electrons Define ionization energy. Describe the concept of electronic shielding and effective nuclear charge (Zeff) and their relationship to trends in ionization energy, atomic radii and ionic radii.