Module 3: Section 1 periodic table (Ionisation Energies (rather important…
Module 3: Section 1 periodic table
The Periodic table
The periodic table is split into blocks, the s block, p block and the d block. This tells you where the outer most electron is placed in an atom of that element
The periodic table is arranged by proton number
A period is the name given to a row of elements and a group is a column of elements
The elements at the end of each period have a full outer shell of electrons and make up the noble gasses as they don't react
The elements in the same group all have similar chemical properties as they have the same number of electrons in their outer shells.
When electrons have been removed from an atom or molecule it has been ionised.
The first ionisation energy is:** The energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms o form 1 mole of gaseous ions
The reactions are endothermic as you have to put energy into them
rather important facts about ionisation energies:
1) Must use the gas state symbol because ionisation energies are measured for gaseous atoms
2) Always refer to 1 mole of atoms instead of 1 atom in the definition
3) The lower the ionisation energy the easier it is to make an ion
Factors that effect ionisation energy
1) nuclear charge: The more protons that are in the nucleus, the more positively charged the nucleus is and the stronger the attraction for the electrons
2) Atomic radius: Attraction falls off very rapidly with distance. An electron close to the nucleus will be much more strongly attracted than one further away
3) Shielding: As the number of electrons between the outer electrons and the nucleus increases the outer electrons feel less attraction towards the nuclear charge.
A high ionisation energy means there is a strong attraction between the electron and the nucleus so more energy is required to overcome the attraction and remove the electron
As you move across a period the general trend is that the ionisation energy increases and the general trend down the group is that the ionisation energies decrease. **However there is an exception to the rule. Between groups 2 and 3 and groups 5 and 6 the ionisation energies drop due to the outer most electron being in a higher energy level so is further away from the nucleus therefore easier to lose
The drop between groups 5 and 6 is down to p sub shell repulsion as the atoms in group 5 have 1 electron in their outer most shell and the atoms in group 6 have 2 electrons in their outher most shell the repulsion between the 2 electrons makes the first electron easier to remove
Successive ionisation energies are the further removal of electrons for ions which requires more energy than the first
The big jumps on the ionisation energy graph are down to electrons being taken from a new shell.
Structure, Bonding and properties
Disproportionation and water treatment
Tests for ions