Periodicity Flashcards
Describe the trend in atomic radius as we move across a period
As we move across a period the atomic numbers of the elements increase resulting in an increased nuclear charge. The extra electrons are also being added to the same shell meaning there is little extra shielding or distance from the nucleus to lessen the pull of the nucleus on the electrons so atomic radius decreases.
Describe the trend in first ionisation energies as we move across a period
As we move across a period the first ionisation energy generally increases due to increased nuclear charge as the number of protons increases. The extra electrons are also being added to the same shell meaning there is little extra shielding or distance to lessen the ionisation energy full stop hence comma it increases full stop
State the exceptions two the trend in first ionisation energies increasing as we move across a period
There are drops between groups two and three, and groups five and six
Explain why the first ionisation energy of magnesium (G2) is greater than that of aluminium (G3)
Aluminium’s outer electron is in a 3p orbital instead of 3s. the 3P orbital is found further from the nucleus and also has additional shielding provided by the 3S electrons. These two factors override the effect of the increased nuclear charge resulting in the ionisation energy dropping slightly.
Explain why the first ionisation energy of phosphorus (G5) is greater done that of sulphur (G6)
In an tom of phosphorus and sulphur the shielding is identical and the electron is being removed from the same orbital. However, in sulphurs case the electron is being removed from a fully occupied orbital. The repulsion between the two electrons means it is easier to remove sulphurs outer electron.
Describe the trend in electronegativity as we move across a period
As we move across a period electronegativity increases. This is due to increased nuclear charge as the atomic numbers of the elements increase. The extra electrons are also being added to the same shell meaning there is little extra shielding or distance to lessen the pull of the nucleus on the shared pair of electrons. So, electronegativity increases.
Explain why the melting points increase as we move across the metal element of a period
As we move across a period the metallic bonding of the elements get stronger. This is because the next element has one more electron in its outer shell done the last so it loses more electrons than the previous element giving them an increasing positive charge. The atomic radius of the elements also decrease, so the delocalised electrons are attracted more strongly to the nucleus. So, more energy is needed to break the bonds and therefore the melting point increases.
Explain why the melting point of silicone is very high
Silicon forms a macromolecular structure. Therefore lots of energy is needed to overcome the many strong covalent bonds between the atoms hence Silicon has a very high melting point.
explain why phosphorus sulphur and chlorine have low melting points
These elements form simple molecular compounds. Between the molecules are very weak van der waals forces which require little energy to break hence they have low melting points.
Explain why organ has a very low melting point
Argon is monoatomic. The only forces you only need to overcome are the very weak van der waals forces between the atoms hence it has a very low melting point and is gas at room temperature.
