AS - Periodicity Flashcards
What is the position of an element in the periodic table determined by?
It’s proton number
An element is classified as s, p, d or f block according to what?
It’s position in the periodic table
The periodic table is a list of elements in order of increasing what?
Atomic/proton number
How are metals and non-metals separated on the periodic table?
A staircase line starting from the top left hand corner of Boron
What are metalloids?
Elements that touch the staircase line separating metals and non metals on the periodic table.
They have a mixture of metallic and non-metallic properties.
Why do elements of the same group have similar properties?
Because they have the same number of electrons in their outer shell
How can you tell how many electrons are found in the outer shell of an element by just looking at the periodic table?
The group number is the number of electrons in that element’s outer shell
What is the trend for atomic radius across period 3 from Na to Ar? Explain your answer.
Atomic radius decreases across a period.
The proton number increases across a period and so the nucleus has a greater positive charged compared to the previous element in the period. This means that there is greater attraction to the outer electrons. Also, there is little shielding effect as the extra electrons added along the period are all found in the same energy level.
What is the trend for ionisation energy across period 3? Explain your answer.
Ionisation energy generally increases across a period, however there are some anomalies.
This is because the proton number increases, therefore the nuclear charge increases causing greater attraction between the nucleus and outer electron. There is little shielding effect as additional electrons across the period are found in the same energy level. Therefore attraction between nucleus and outer electron is stronger and requires more energy to break.
Where are the anomalies found when looking at the trend in ionisation energy across a period?
Explain why these anomalies exist.
- Between group 2 and 3 where there is a decrease in ionisation energy.
This is because the group 3 element has its outer electron in a p orbital, whereas the group 2 element has its outer electron in the s orbital. The p orbital is further from the nucleus and shielded by the s orbital meaning it takes less energy to remove this electron.
- Between group 5 and 6 where there is a decrease in ionisation energy.
This is because the element in group 6 has its outer electron in a pair so is repulsed by the other electron in the pair, meaning it takes less energy to remove this outer electron. The element in group 5 has no paired electrons in the p orbital so repulsion is not a factor.
Melting points vary across a period. What does the melting point of an element depend on?
The structure and bonding of an element.
Describe the trend in melting points between sodium to aluminium in period 3.
Melting points increase across these elements. The elements all have a metal structure with metallic bonding. The melting point increases across them as the metallic bonds get stronger across the period. This is because the nucleus has an increasing positive charge, and there is an increasing number of delocalised electrons, so the force of attraction between these increases across the period.
How does the melting point of silicon compare to the melting point of the previous element in period 3, aluminium?
Explain your answer.
Silicon has a very high melting point, much higher than that of aluminium.
This is because it has a macro molecular structure with lots of very strong covalent bonds holding the structure together. A lot of energy is required to break these bonds.
Give the molecular formulae of phosphorous, sulfur and chlorine.
P4, S8 and Cl2
Describe and explain the trend in melting points from P to Cl, with reference to silicon.
P4, S8 and Cl2 are all molecular substances. The forces acting between these molecules are van der Waals forces which are very weak. The more atoms in a molecule mean the stronger the VDWs forces. Therefore P has a much lower melting point compared to silicon and a lower melting point compared to sulphur. Chlorine has a lower melting point compared to both P and S because it is the smallest molecule out of the three.
VDWs forces are easily overcome which is why the melting point of simple molecular structures is low.
