Unit 2: Section 1- Periodicity Flashcards
Define periodicity
Periodicity is the study of patterns in the chemical or physical properties of elements going across the periods of the periodic table
What are the four blocks that the periodic table is divided up into?
s, p, d and f
What does the block that an element is in depend upon?
It depends on the orbital in which the outermost electron, the valence electron, of the element is found.
What block are Group 1 and 2 elements found in?
s
What block are Group 3 elements found in?
p
What elements are found in block d?
the transition metals
Where can the f block be found?
below the periodic table
What is the trend between atomic radius and moving left to right across a period?
atomic radius decreases
Explain why the atomic radius decreases going from left to right across a period
As we go across a period the number of protons found in the elements nucleus increases. This increases the nuclear charge of the elements, thereby creating a stronger electrostatic attraction between the nucleus and the electrons of the element
The same amount of shielding is present across the period, so the nucleus of an element is able to pull its valence electrons closer to itself
What is shielding?
It is the electrostatic repulsion felt between negatively charged electrons and how much this cancels out the attraction of electrons to the nucleus
What is the trend in shielding across a period and why?
It stays roughly the same, because the outer electron from each element in a period is found in the same shell
Define first ionisation energy
enthalpy change when one mole of gaseous atoms forms one mole gaseous ions (1+ charge)
What happens to first ionisation energy moving across a period?
It increases, so more energy is needed to remove the valence electron from the element to form an ion
Explain why first ionisation energy increases along a period
Increasing nuclear charge and attraction leads to an increase in first ionisation energy
As shielding remains similar, there is no significant increase in repulsion of this outer electron and so ionisation energy increases
Name four exceptions to the trend of increasing first ionisation energy
Magnesium and Aluminium
Phosphorus and Sulfur