Unit 2: Section 1- Periodicity Flashcards
Define periodicity
REPEATING patterns across a period
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
What happens to the trend in first ionisation energy between magnesium and aluminium?
Between magnesium and aluminium, there is a drop in the 1st ionisation energy.
Why is there a drop in first ionisation energy between magnesium and aluminium?
- the outer electron of Mg is in the 3s subshell while the outer electron of Al is in the 3p subshell.
- so, when removing an electron from the Al outer shell, the electron is being removed from a 3p subshell which has a higher energy than the 3s subshell
- the higher energy level makes it easier for an electron to be removed, decreasing the energy required to remove the electron
What happens to the trend in first ionisation energy between phosphorous and sulfur?
Between phosphorous and sulfur, there is a drop in the 1st ionisation energy.
Why is there a drop in first ionisation energy between phosphorous and sulfur?
- the outer electron of sulfur is paired up, however the outer electron of phosphorous is not, even though they are both in the 3p orbital
- this causes a small repulsion between the two electrons (S) making it easier for an electron to be removed
- It is also more energetically favourable for the atom to have an exactly half full subshell. Sulfur can lose its outer electron to gain an exactly half filled subshell.
What are the trends for first ionisation energy in period 3?
The trends for Period 3 are the exact same for Period 2. Except that the drops are between berylium and boron and nitrogen and oxygen. In an explanation, make sure to change 3p/3s orbitals to 2p/2s.
What is the trend in MP and BP in elements across a period?
There is no general trend in the melting and boiling points of elements across a period. Instead a number of factors determine the individual temperatures at which each elements will melt and boil.
What happens to the MP/BP betwen Na to Al?
MP/BP increases
Why does MP/BP increase between Na and Al?
- There is an increase in the strength of metallic bonding.
- The metallic bonds become stronger because the number of delocalised electrons increases across the period while the ions become smaller with a greater positive charge.
- To break these bonds, a high energy is required.
What type of MP/BP does Si have?
very high
Why does Si have a very high MP/BP?
Silicon exists a macromolecule and therefore has lots of strong covalent bonds within it. A lot of energy is required to break these bonds so it has a very high melting and boiling point.
Why do Cl, S and P all have low MP/BPs?
They are all simple molecules that contain weak Van der Waals forces. Therefore, not a lot of energy is needed to break the bonds so they have low boiling and melting points.
What type of MP/BP do Cl, S, and P all have?
Low
Why does the MP/BP slightly increase between phosphorous and sulfur?
Because the sulfur molecule (S8)
has more electrons than the phosphorus molecule (P4) , so it has stronger Van der Waals forces.
What happens to the MP/BP between P and S?
it slightly increases
What type of MP/BP does Ar have?
low
Why does Ar have a low MP/BP?
It is a monoatomic element and therefor has weak Van der Waals forces and so a low MP/BP
What is the trend in MP/BP in period 3?
The trends in Period 3 are similar in Period 2, except that while lithium and beryllium Be are both metals, boron is not a metal and is in fact a macromolecule so will have a very high melting point compared to the metals.
How can you easily find the electronic structure of an element using the periodic table?
Label each block of the periodic table, with the groups and 1s, 2s, 2p, 3s, 3p… etc
Then read off electron configuration
Each period has a higher energy level
