Electron Configurations and Periodic Trends

Review

• What information can we get from the Periodic Table?

• How can we classify elements on the Periodic Table?

• What model of the atom do we use today? What does an atom look like?

Electron Configurations

• The ways in which electrons are arranged in various orbitals around the nuclei of atoms are called electron configurations.

• These will tell you where we can expect to find electrons based upon their energy.

• Lowest energy = closer to the nucleus• Higher energy = further away

Orbitals

• Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.

• s, p, d, and f orbitals

S orbitals

P orbitals

S with p orbitals

d orbitals

f orbitals

Review

Electron Configurations

3 rules to finding Electron Configurations1. Aufbau Principle: electrons occupy

the orbitals of lowest energy first. 2. Pauli Exclusion Principle: only two

electrons per atomic orbital.3. Hund’s rule: electrons occupy orbitals of the same energy in a way to maximize the total spin.

Practice

CarbonArgonNickelSiliconSulfurSelenium

Independent Practice

• What trends do you see with the electron configurations?

Now, I’ll teach you a short cut based on these trends.

Periodic Trends

• Atomic size• Size of its ion• Ionization energy• Electronegativity

Atomic Size • Measured as half the distance between two

nuclei of the same atom when they are joined. • In general, the size increases from top to

bottom within a group and decreases left to right across a period.

Practice with Atomic size

1. Give the larger of the two atomsCarbon or Nitrogen?Phosphorus or Arsenic?

2. Put the following elements in order of increasing atomic size: potassium, calcium, sodium and magnesium

Ionic size trends?

• Same as atomic size

Which ion would be larger: sodium or magnesium? Sulfur or selenium?

Put the following ions in order of decreasing size: sodium, magnesium, sulfur and selenium.

Trends in Ionization Energy

• Remember: electrons can move to higher energy levels

• Sometimes, enough energy is gained to remove the electron completely (ionization energy).

• Tends to decrease from top to bottom within a group and increase from left to right across a period.

Trends in Electronegativity

• Ability to attract electrons • In general, electronegativity decreases from

top to bottom and increase across a period left to right. (same as ionization energy)

Practice Which would have more affinity to attract

electrons: Fluorine or chlorine?

Which atom would lose an electron easier: lithium or sodium?

Open Note Check Quiz

1. How does atomic size change within groups and across periods?

2. When do ions form?3. How does electronegativity vary on the periodic table? 4. Arrange these elements in order of decreasing atomic

size: sulfur, chlorine, aluminum, and sodium. 5. Which element in each pair has the larger first

ionization energy? a. Sodium, potassiumb. Magnesium, phosphorus

Independent Practice

• Electron configurations and Periodic Trends • Finish notes with questions and a summary• Update glossary with all key terms thus far!

Key Terms: anion, cation, ion, electronegativity, ionization energy, electron configuration, atom, atomic number, electron, proton, neutron, isotopes, group, period, nucleus