3.1.1 periodicity Flashcards
Elements in groups
Have similar physical and chemical properties
Atoms of elements in a group have similar outer shell electron configurations, resulting in similar chemical properties
Classification of elements in s,p,d blocks
Elements are classified based on which orbitals the highest energy electrons are in
Periodicity
Repeating pattern of properties across different periods
Atomic radius
Decreases across a period as increase proton number creates more positive charge attraction for electrons which are in the same shell
Similar shielding
First ionisation energy
Energy needed to remove an electron from each atom in one mole of gaseous atoms
H(g) > H+(g) + e-
Factors affecting ionisation energy
Attraction of nucleus (the more protons the greater the attraction)
The distance of electrons from nucleus (the bigger the atom the further the outer electrons are from the nucleus and the weaker the attraction to the nucleus)
Shielding of attraction of nucleus (an electron in outer shell is repelled by electrons in complete inner shells, weakening the attraction of the nucleus)
Successive ionisation energy
Always larger than first ionisation energy
This is because the ion formed, is smaller than the atom and the proton to electron ratio in the 2+ ion is greater than the 1+ ion
Attraction between nucleus and electron is therefore stronger
Why has helium the largest first ionisation energy
It’s first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells
Has a bigger first ionisation energy than H as it has one more proton
Why do first ionisation energies decrease down a group
As one goes down a group, the outer electrons are found in shells further from the nucleus
more shielded so the attraction of the nucleus becomes smaller
Why is there a general increase in first ionisation energy across a period
As one goes across a period the electrons are being added to the same shell which has the same distance from the nucleus and same shielding effect.
The number of protons increases, however, making the effective attraction of the nucleus greater.
Why has Na a much lower first ionisation energy than Neon?
This is because Na will have its outer electron in a 3s shell further from the nucleus and is more shielded.
So Na’s outer electron is easier to remove and has a lower ionisation energy.
Why is there a small drop from Mg to Al
Al is starting to fill a 3p sub shell, whereas Mg has its outer electrons in the 3s sub shell.
The electrons in the 3p subshell are slightly easier to remove because the 3p electrons are higher in energy and are also slightly shielded by the 3s electrons
Why is there a small drop from P to S
With sulphur there are 4 electrons in the 3p sub shell and the 4th is starting to doubly fill the first 3p orbital.
When the second electron is added to a 3p orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove.
Metallic bonding
the electrostatic force of attraction between the positive metal ions and the delocalised electrons
3 main factors affecting strength of metallic bonding
Number of protons - the more protons the stronger the bond
Number of delocalised electrons per atom - the more delocalised electrons the stronger the bond
Size of ion - the smaller the ion, the stronger the bond
