ionisation energy and electron shells

ionisation energy and electron shells

1. Ionisation energy is the energy required to remove 1 mole of electrons from one mole of atoms in the gaseous state. Ionisation energy is always positive because energy is put in to remove the electron. Ionisation energy increases as you go across a period because protons are being and the number of shells is still the same, causing the ionic radius to decrease. However, as you go down the group the ionisation energy decreases because there are more shells being added to the atom, plus there is more shielding therefore the attraction between the protons and electrons becomes weaker.

2. Atoms are mad up of shells

   • Within the shells there are sub shells
     • within the sub shells there are orbitals

3. Evidence for electron shells, which are shells that surround the nucleus of an atom. The outermost shell in an atom, also called valency shell. The principle quantum number tells you which shell it is.

   • The series of successive ionisation energies for an element, this provides evidence for the existence of electron shells. As you remove electrons from the valency shell you realise that there is jump in the ionisation energy required to remove the electron. This is due to the fact that, these electrons are on shells that are closer to the nucleus, therefore there is a stronger attraction between positively charged protons and negatively charged electron, plus there is less shielding from electrons so the strength of the attraction is enhanced. On top of that, the first big jump specifies which group the element is in, also keep in mind when electrons are removed they get removed from the valency shell fist and then work their way.

4. Evidence for sub-shells, which are where one or more orbitals in the electron shell of an atom with the same energy level. There are different types of sub-shells, S,P,D and F.

   • The first ionisation energy of successive elements shows evidence for the existence of sub-shells. As you go across the period, the ionic radius decreases and the ionisation energy increases. This is due to, the number of protons increases as you go across the period, however the number of shells is still the same. Therefore, there is a stronger attraction between the positively charged protons and negatively charged electrons. As a result, in the graph of the first ionisation energy there are small drops between elements, because they are entering new sub-shells, and it requires less energy to remove an electron from that new shell rather than removing an electron from a half full sub-shell, because half full sub-shells are more stable.

5. Orbitals are regions of space around the nucleus of an atom where an electron is likely to be found. The shape of the S orbital is spherical and the P orbital is a dumb-bell shaped. Each orbital is occupied by 2 electrons that have opposite spin. The S sub-shell has only one S orbital, but the P sub-shell has 3 P orbitals, the D sub-shell has 5 Orbitals and the F sub-shell has 7 F orbitals. The electron density map of electron orbitals shows how the electron cloud is distributed within the orbital.

6. Electronic configuration

   • The order of filling or orbitals is dependant on the energy level of the sub-shell, so the 1S sub-shell fills up first because it is at a lower energy level. Plus electrons fill up orbitals singly before pairing up, which is according to Hund's rule. However, when writing the electronic configuration for an element the 4S orbital fills up first before the 3D orbital but the 3D orbital is written before it.

7. Atoms such as neon get excited, which means that electrons are raised from their ground state to a higher energy level, this happens as the electron gains kinetic energy, and that energy is given out as light energy causing the electron to return to its ground state.

8. Trends in the melting temperatures.

   • These trends are due to the variety in types of bonding and structures within the periodic table. As you move across the period the melting point increases to a certain point then drops. Group 1,2 and 3 contain bonds the are made from metallic bonds which are very strong, because they are held together by a sea of delocalised electrons, and the melting point increases as you go across these groups because there are more shared delocalised electrons. In group 4 the melting point is still high because the hint molecular structures are held together by strong covalent bonds and strong intermolecular forces of attraction making have a higher melting point that elements with metallic bonds. But in groups 5-8, these elements are made up of simple molecular covalent bonds which have weak intermolecular London dispersion forces of attraction between molecules that can be easily overcome, hence they have a low melting point.