Atomic Structure HL only

12.1 Electron configuration The first ionisation energy is defined as the amount of energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a 1+ charge. X (g)  X + (g) + e - The second and third ionisation energies refer to the energy changes for the reactions: X + (g)  X 2+ (g) + e - X 2+ (g)  X 3+ (g) + e - The higher the value, the harder it is to remove an electron. Now do the “Ionisation Energy” exercise.

Which group is this element in? Group 4 Notice the “jump” in energy needed to remove the 5 th electron Ionisation energies and group numbers

Which group is this element in? Group 2 Notice the “jump” in energy needed to remove the 3 rd electron Ionisation energies and group numbers

Which group is this element in? Group 3 Notice the “jump” in energy needed to remove the 4 th electron Ionisation energies and group numbers

Which group is this element in? Group 5 Notice the “jump” in energy needed to remove the 6 th electron Ionisation energies and group numbers

Which group is this element in? Group 1 Notice the “jump” in energy needed to remove the 2 nd electron Ionisation energies and group numbers

Electron Arrangements Electrons are arranged in: Energy levels (or shells) Labelled 1, 2, 3, 4 etc Sub-levels (or sub shells) Labelled s, p, d or f Split into orbitals: s sub-level – 1 orbital p sub-level – 3 orbitals d sub-level – 5 orbitals f sub-level – 7 orbitals

Copy and complete the table below: Principal quantum number Number of each type of orbital Maximum number of electrons in level spdf

Differences in shielding from the nucleus cause different sub-levels to have slightly different energies.

Writing Electron arrangements 1.Energy levels fill from lowest first – Aufbau Principal  Hydrogen (Z = 1) has electron arrangement 1s 1 2.An orbital can contain a maximum of 2 electrons and then only if they have opposite spins – Hund’s rule  Lithium (Z = 3) has the electron arrangement 1s 2 2s 1 The electrons in the 1s orbital have opposite spins. but notor

3.Orbitals must be occupied singly and with parallel spins before they can be occupied in pairs – Pauli exclusion principal  Nitrogen (Z = 7) has the electron arrangement 1s 2 2s 2 2p 3 With the electrons in the 2p sub-level in different orbitals: and not Write down the electron arrangements of H to Xe in the form 1s etc.

Note these two exceptions to the expected pattern, both of which stem from the 4s and 3d levels being very close in energy: Cr1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 This is a slightly lower energy arrangement as the reduced electron repulsion makes up for the fact one electron is in a slightly higher energy level. Cu1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10 This is a slightly lower energy arrangement. In ions, the electrons in the highest energy levels are lost first, but note that when losing electrons, electrons are lost from 4s before 3d (the energy levels are very close, and when electrons fill them, 4s goes above 3d).

Abbreviated forms of electron arrangements can also be used. For example: For Z = 23 the full electron arrangement is ……………. But this can be shortened to: [Ar] 4s 2 3d 3 See worksheet.

What are orbitals? When a planet moves around the sun, you can plot a definite path for it which is called an orbit. A simple view of the atom looks similar (Bohr’s model). However, electrons in fact inhabit regions of space known as orbitals. To plot a path for something you need to know exactly where the object is and be able to work out exactly where it's going to be an instant later. You can't do this for electrons. The Heisenberg Uncertainty Principle says - loosely - that you can't know with certainty both where an electron is and where it's going next.

Consider hydrogen: Suppose you had a single hydrogen atom and at a particular instant plotted the position of the one electron. Soon afterwards, you do the same thing, and find that it is in a new position. You have no idea how it got from the first place to the second. You keep on doing this over and over again, and gradually build up a sort of 3d map of the places that the electron is likely to be found. 90 % of the time, the electron will be found within a fairly easily defined region of space quite close to the nucleus. Such a region of space is called an orbital.