Periodicity Flashcards
What happens to the atomic radius as you go across the period?
the atomic radius decreases
more protons are added so the positive charge of the nucleus increases so the electrons are pulled closer to the nucleus.
why does the atomic radius decrease across a period?
As more protons are added this means there s a greater positive charge on the nucleus so the electrons which are being added to the same shell, are pulled closer. each electron is added to the same shell which also means that there is no aded shielding.
what happens when a substance melts?
the attractive forces holding the particles together are broken or loosed so that the partickes can move around more freely but are still close together.
the stronger the forces the more energy is needed to over come them.
what is the general trend in the melting points of the elements in period 3?
the melting point increases between sodium and silicon but then decreases between silicon and argon.
Why does the melting point increase from Sodium to Aluminium in Period 3?
Na, Mg and Al are metals with a metallic structure so as more protons are added the positive nuclear charge increases and the number of delocalised electrons increases, this means that there is moe electrostatic attraction between the positive ions and the electrons and a smaller atomic radius. This means that it will take more energy to over come this attraction.
Why does silicon have the highest melting point in period 3?
it has a macromolecular (giant Covalent) structure. Similar to diamond, each Si atom bone to 4 others in a tetrahedral structure and giant lattice structure. many Very strong covalent bonds have o be broken in order for it to melt so it requires a very large amount of energy to overcome them.
Why do Phosphorus, Sulphur, Chlorine and Argon have lower melting points?
Only held together by Van der Waals forces which are weak and do not require much energy to over come them.
P, S, Cl - simple covalent molecules, strong covalent bonds between atoms but weak Van der Vaals between molecules.
Ar - single atoms
why does sulphur have a higher melting point than Phosphorus and Chlorine?
exists and S8 so more Van der Waals
what is the general trend in first ionisation energies cross period 3?
An Increase
What is the reason for the trend in first ionisation energies across period 3?
more protons so more attraction between outershell electrons an nucleus
Explain the reason why the atomic radius of aluminium is larger that the atomic radius of sulphur?
Al 13 protons, S has 16 so S has greater positive nuclear charge so electrons pulled closer to the nucleus
Name a period 3 element with a larger atomic radius than Al
Na/Mg
Explain why the first ionisation energy of sulphur is higher than aluminium
S has more protons, so electrons attracted more strongly towards nucleus. so more energy required to remove an electron from the outer shell higher ie
Why is the melting point of phosphorus lower than silicon?
Silicon is Macromolecular so strong covalent bonds link all atoms together whee as P is a molecular structure so only has Van der Waals forces between its molecules. it takes a lot less energy to over come Van der Waals than covalent bonds so therefore P has a lower melting point.
Name a period 3 element with a lower melting point than phosphorus
Cl/Ar
