Advanced Higher Advanced Higher ChemistryChemistry

Unit 1 Unit 1

Writing electronic structuresWriting electronic structures

Electronic ConfigurationElectronic Configuration

• The electronic configuration for The electronic configuration for hydrogen is 1shydrogen is 1s11, for helium 1s, for helium 1s22 and and for lithium 1sfor lithium 1s22 2s 2s11

• This means that for hydrogen there This means that for hydrogen there is one electron in the 1s orbital, for is one electron in the 1s orbital, for helium 2 electrons in the 1s orbital helium 2 electrons in the 1s orbital and for lithium, 2 electrons in the and for lithium, 2 electrons in the 1s orbital and 1 in the 2s orbital.1s orbital and 1 in the 2s orbital.

Orbital box notationOrbital box notation Hydrogen has one Hydrogen has one

electron (represented by electron (represented by an arrow). This is found an arrow). This is found in the 1s subshell. in the 1s subshell.

Helium has two Helium has two electrons. These are also electrons. These are also found in the 1s subshell. found in the 1s subshell. Due to Hund’s rule these Due to Hund’s rule these electrons have opposing electrons have opposing spins (represented by spins (represented by the arrows pointing in the arrows pointing in opposite directions).opposite directions).

1s

1s

Orbital box notationOrbital box notation

The following diagrams represent the orbital box notation for lithium and carbon

Orbital Box NotationOrbital Box Notation

• The orbital box notation for oxygen The orbital box notation for oxygen is below.is below.

Electrons fill the 4s orbital before the 3d Electrons fill the 4s orbital before the 3d orbital because the 4s orbital has a orbital because the 4s orbital has a lower energy.lower energy.

There are two exceptions to this ruleThere are two exceptions to this rule- chromium which has one electron in - chromium which has one electron in its 4s orbital and five in its 3d orbitals.its 4s orbital and five in its 3d orbitals.- copper which has one electron in its 4s - copper which has one electron in its 4s orbital and ten in its 3d orbitals. orbital and ten in its 3d orbitals. (See later slides on ionisation energies (See later slides on ionisation energies for an explanation)for an explanation)

Periodic TablePeriodic Table• Groups 1 and 2 of the Periodic Table Groups 1 and 2 of the Periodic Table

are known as the s-block as the are known as the s-block as the outermost electrons can be found in s outermost electrons can be found in s orbitals.orbitals.

• Groups 3 to 0 are known as the p-block Groups 3 to 0 are known as the p-block elements as the outermost electrons elements as the outermost electrons can be found in p orbitals.can be found in p orbitals.

• The transition metals are d-block The transition metals are d-block elements.elements.

• f-block elements are elements 57 to 71 f-block elements are elements 57 to 71 and 89 to 103.and 89 to 103.

Ionisation EnergyIonisation Energy

• First ionisation energy = energy First ionisation energy = energy required to remove one mole of required to remove one mole of electrons from one mole of gaseous electrons from one mole of gaseous atoms.atoms.

• In GENERAL, ionisation increases In GENERAL, ionisation increases across a period due to the increasing across a period due to the increasing positive charge of the nucleus and it positive charge of the nucleus and it decreases down a group as the outer decreases down a group as the outer electrons are shielded from the electrons are shielded from the nucleus by the inner electrons.nucleus by the inner electrons.

Ionisation EnergyIonisation Energy• Be has a 1Be has a 1stst I.E. of 905 kJ mol I.E. of 905 kJ mol-1-1

B has a 1B has a 1stst I.E. of 807 kJ mol I.E. of 807 kJ mol-1-1

• This is because of the electronic This is because of the electronic configuration:configuration: Be 1sBe 1s22 2s 2s22

B 1sB 1s22 2s 2s22 2p 2p11

• The first ionisation energy of Boron is The first ionisation energy of Boron is lower as the electron is removed from lower as the electron is removed from an incomplete orbital which is less an incomplete orbital which is less stable than if it were complete.stable than if it were complete.

• Complete orbitals are more stable than Complete orbitals are more stable than incomplete orbitalsincomplete orbitals

Ionisation EnergyIonisation Energy

• Nitrogen also has a higher first Nitrogen also has a higher first ionisation energy than oxygen as ionisation energy than oxygen as the electron is removed from a half the electron is removed from a half full subshell.full subshell.

• Half full subshells are more stable.Half full subshells are more stable.