Advanced Higher Chemistry Unit 1 Writing electronic structures

Electronic Configuration The electronic configuration for hydrogen is 1s 1, for helium 1s 2 and for lithium 1s 2 2s 1 The electronic configuration for hydrogen is 1s 1, for helium 1s 2 and for lithium 1s 2 2s 1 This means that for hydrogen there is one electron in the 1s orbital, for helium 2 electrons in the 1s orbital and for lithium, 2 electrons in the 1s orbital and 1 in the 2s orbital. This means that for hydrogen there is one electron in the 1s orbital, for helium 2 electrons in the 1s orbital and for lithium, 2 electrons in the 1s orbital and 1 in the 2s orbital.

Orbital box notation n Hydrogen has one electron (represented by an arrow). This is found in the 1s subshell. n Helium has two electrons. These are also found in the 1s subshell. Due to Hund’s rule these electrons have opposing spins (represented by the arrows pointing in opposite directions).

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

Orbital Box Notation The orbital box notation for oxygen is below. The orbital box notation for oxygen is below.

n Electrons fill the 4s orbital before the 3d orbital because the 4s orbital has a lower energy. n There are two exceptions to this rule - chromium which has one electron in its 4s orbital and five in its 3d orbitals. - copper which has one electron in its 4s orbital and ten in its 3d orbitals. (See later slides on ionisation energies for an explanation)

Periodic Table Groups 1 and 2 of the Periodic Table are known as the s-block as the outermost electrons can be found in s orbitals. Groups 1 and 2 of the Periodic Table are known as the s-block as the outermost electrons can be found in s orbitals. Groups 3 to 0 are known as the p-block elements as the outermost electrons can be found in p orbitals. Groups 3 to 0 are known as the p-block elements as the outermost electrons can be found in p orbitals. The transition metals are d-block elements. The transition metals are d-block elements. f-block elements are elements 57 to 71 and 89 to 103. f-block elements are elements 57 to 71 and 89 to 103.

Ionisation Energy First ionisation energy = energy required to remove one mole of electrons from one mole of gaseous atoms. First ionisation energy = energy required to remove one mole of electrons from one mole of gaseous atoms. In GENERAL, ionisation increases across a period due to the increasing positive charge of the nucleus and it decreases down a group as the outer electrons are shielded from the nucleus by the inner electrons. In GENERAL, ionisation increases across a period due to the increasing positive charge of the nucleus and it decreases down a group as the outer electrons are shielded from the nucleus by the inner electrons.

Ionisation Energy Be has a 1 st I.E. of 905 kJ mol -1 Be has a 1 st I.E. of 905 kJ mol -1 B has a 1 st I.E. of 807 kJ mol -1 This is because of the electronic configuration:Be 1s 2 2s 2 This is because of the electronic configuration:Be 1s 2 2s 2 B 1s 2 2s 2 2p 1 The first ionisation energy of Boron is lower as the electron is removed from an incomplete orbital which is less stable than if it were complete. The first ionisation energy of Boron is lower as the electron is removed from an incomplete orbital which is less stable than if it were complete. Complete orbitals are more stable than incomplete orbitals Complete orbitals are more stable than incomplete orbitals

Ionisation Energy Nitrogen also has a higher first ionisation energy than oxygen as the electron is removed from a half full subshell. Nitrogen also has a higher first ionisation energy than oxygen as the electron is removed from a half full subshell. Half full subshells are more stable. Half full subshells are more stable.