Periodicity Flashcards
What is the structure of the periodic table
The periodic table is the arrangement of elements by increasing atomic number. They are arranged in groups which have similar chemical properties.
Periodicity
Repeating physical and chemical properties across the period
Classification of elements due to their orbitals
Elements are classified as s, p or d block, according to which orbitals the highest energy electrons are in
How does atomic radius change across the period
Atomic radius decreases as you move from left to right across the period due to the increases number of protons which causes an increase in nuclear charge, so the electrons feel more attraction.
First ionisation energy
The energy needed to remove an electron from each atom in a mole of gaseous atoms
Factors which affect ionisation energy
The greater the nuclear charge, the higher the ionisation energy. The greater the atomic radius the lower the ionisation energy. The greater the shielding the lower the ionisation energy.
Why are successive ionisation energies always larger?
The second ionisation energy is always bigger then the first. This is because the proton to electron ratio is bigger and each electron feels more attraction from the nucleus. More energy is need to overcome this attraction and loose the electron.
How are ionisation energies linked to electronic structure
There will be a big jump in ionisation energy at the end of a sub shell as there is less shielding. So if there is a big increase between the 2nd and 3rd ionisation energy then you know it is in group 2.
How does ionisation energy change down the group
It decreases down the group as atomic radius and shielding increases which outweighs the increase in nuclear charge meaning more energy is required to loose an electron.
How does ionisation energy change across the period
As you move across the period the atomic radius and shielding remains the same. However, each element has one more proton which increases the nuclear charge so increase the ionisation energy. There is a slight decrees in ionisation energy when a new shell begins as they now experience shielding from the full sub shell.
Why is there a decrease in ionisation energy between group 5 and 6
In group 6 there are 4 electrons in the 3p sub shell and the 4th is paired up with the first electron and they are both in the same orbital. This causes a slight repulsion between the 2 negatively charged electrons which makes the second electron in the orbital easier to remove. Electron pair repulsion theory.
Melting and boiling point changes across the period
For Na, Mg and Al there is metallic bonding. This is strong bonding which gets stronger the more electrons there are in the outer shell as they are donated to the sea of delocalised electrons. There is a giant increase at Si as its a giant covalent structure and there are strong covalent bonds between atoms. There is a decrease after that as the molecules are simple molecular and there are weak London forces between molecules which is easy to overcome.
