Periodic Properties of Periodic Properties of ElementsElements

Chapter 7 part IChapter 7 part I

Periodic trends in OrbitalsPeriodic trends in Orbitals

Periodic Trends in Electron Periodic Trends in Electron OrbitalsOrbitals

Exceptions to the rulesExceptions to the rules

Chromium and Chromium and Copper do not follow Copper do not follow the expected the expected electron electron configuration.configuration.

Cr is expected to be Cr is expected to be [Ar]4s[Ar]4s223d3d44

Cu is expected to be Cu is expected to be [Ar]4s[Ar]4s223d3d99

Ionization energyIonization energy

The energy required The energy required to remove one to remove one electron from a electron from a gaseous element or gaseous element or ion.ion.

Ionization Energy (kJ/mol)Ionization Energy (kJ/mol)

1st1st 2nd2nd 3rd3rd 4th4th 5th5th

LiLi 520520 72987298 1181511815

BeBe 899899 17571757 18491849 2100621006

BB 801801 24272427 36603660 2502625026 3282732827

CC 10861086 23532353 46204620 62226222 3783037830

Ionization energyIonization energy First ionization energy First ionization energy

is the energy required is the energy required to remove the highest to remove the highest energy electron.energy electron.

As the number of As the number of protons increase, protons increase, generally it is more generally it is more difficult to remove an difficult to remove an electron until a shell is electron until a shell is completed.completed.

Periodic Trends in Ionization Periodic Trends in Ionization EnergyEnergy

QuestionsQuestions

Which of these Which of these atoms has the atoms has the largest 1st largest 1st ionization energy?ionization energy?

2nd? 2nd? Which has the Which has the

smallest?smallest? Why?Why?

1s1s222s2s222p2p66

1s1s222s2s222p2p663s3s11

1s1s222s2s222p2p663s3s22

SolutionSolution Ne (1sNe (1s222s2s222p2p66) has ) has

the highest 1st the highest 1st ionization energy as ionization energy as it has a complete s p it has a complete s p shell.shell.

Na (1sNa (1s222s2s222p2p663s3s11) ) has the lowest 1st has the lowest 1st due to shielding.due to shielding.

2nd: Highest 2nd: Highest Na+(1sNa+(1s222s2s222p2p66))

2nd: Lowest 2nd: Lowest Mg+(1sMg+(1s222s2s222p2p663s3s11) ) due to shielding.due to shielding.

What is shielding?What is shielding? Shielding is the Shielding is the

description of a description of a complete electron complete electron shell (core electrons) shell (core electrons) and its “neutralizing” and its “neutralizing” of the positive charge of the positive charge of the nucleus. This of the nucleus. This causes outer shell causes outer shell electrons to be bound electrons to be bound less strongly to the less strongly to the atom.atom.

Electron AffinityElectron Affinity

The energy change The energy change associated with the associated with the addition of an addition of an electron to an atom electron to an atom in its gaseous in its gaseous state.state.

Electron AffinityElectron Affinity

Is often referred to as Is often referred to as the energy released the energy released when an atom when an atom accepts an electron.accepts an electron.

The more negative The more negative the number the more the number the more energy released.energy released.

Atomic radiusAtomic radius

These values are These values are obtained by obtained by measuring the measuring the distance between distance between atoms in chemical atoms in chemical compounds.compounds.

These values may be These values may be smaller than the 90% smaller than the 90% of the electron of the electron density. Why?density. Why?

Atomic radius of ionsAtomic radius of ions

When electrons are When electrons are added to an atom one added to an atom one would expect an would expect an increase in the radius.increase in the radius.

One would also One would also expect a decrease in expect a decrease in radius when an radius when an electron is removed.electron is removed.

Atomic radiusAtomic radius

But why does the radius of the atom decrease with each But why does the radius of the atom decrease with each increase in atomic number???increase in atomic number???

Other trends: Metallic Other trends: Metallic CharacterCharacter