Easy summary for Electron In Atoms a level chemistry

Easy summary for Electron In Atoms a level chemistry cameroon gce revision

Learning outcomes
You should be able to:

■ describe the number and relative energies of the s, p and d orbitals for the principal quantum numbers 1, 2 and 3 and also the 4s and 4p orbitals

■ describe the shapes of s and p orbitals ■

■ state the electronic configuration of atoms and ions given the proton number and charge, using the convention 1s2 2s2 2p6 , etc. ■

■ explain and use the term ionisation energy, and the factors influencing the ionisation energies of elements ■

■ use ionisation energy data to:
– explain the trends across a period and down a group of the Periodic Table
– deduce the electronic configurations of elements ■

■ interpret successive ionisation energy data of an element in terms of the position of that element within the Periodic Table.

Summary
■ Electrons in an atom can exist only in certain energy levels (shells) outside the nucleus.

■ The main energy levels (shells) are given principal quantum numbers n = 1, 2, 3, 4, etc. The lowest energy level (n = 1) is closest to the nucleus.

■ The shells may be divided into subshells known as s, p and d subshells, which can hold a maximum of 2, 6 and 10 electrons, respectively.

■ The region of space in which an electron is likely to be found is called an orbital. Each subshell has a number of orbitals which can each hold a maximum of two electrons. Subshells s, p and d have 1, 3 and 5 orbitals, respectively.

■ The s orbitals are spherical in shape. The p orbitals have two ‘lobes’.

■ When two electrons are present in an orbital they spin in opposite directions and are said to be paired.

■ The electronic configuration of atoms is found by adding electrons to each orbital starting from those in the lowest energy level.

■ When electrons are added to orbitals in the same subshell they go into separate orbitals if possible. Electrons pair up where this is not possible.

■ The 1st ionisation energy of an element is the energy needed to remove one electron from each atom in one mole of atoms of the element in the gaseous state (to form gaseous 1+ ions).

■ The ionisation energies needed to remove the first, second, third, fourth, etc., electrons from each atom or ion in a mole of gaseous atoms are called successive ionisation energies.

■ The magnitude of the ionisation energy depends on these four factors: – the distance of the electron from the nucleus – the number of positive charges in the nucleus – the degree of shielding of outer electrons by inner electron shells – spin-pair repulsion.

■ The trends in 1st ionisation energy of the elements across a period and down a group can be explained using the four factors above.

■ Values of successive ionisation energies of atoms provide evidence for their electronic configuration.