Trends along Period 3 | A Level Chemistry | OCR, AQA, Edexcel
Unlock full course: https://studymind.co.uk/online-course...
Our A-Level Chemistry Experts are here to help you ace A-Level Chemistry!
This week we are revising Trends along Period 3
A-Level Chemistry can be tough but fortunately we’ve made this tutorial to help you score the A* you need for questions on everything to do with Trends along Period 3.
Subscribe to Study Mind: https://www.youtube.com/c/StudyMind?s...
Free Revision Notes: https://studymind.co.uk/revision-note...
Free Past Papers: https://studymind.co.uk/resources/
Periodicity refers to the repeating pattern in physical and chemical properties of the elements across a period of the periodic table.
The atomic radius of an element decreases as you move across a period. The proton number of the element increases as you move across a period which means that the number of protons increases. The nucleus gains a more positive charge as the number of protons increases. This means there is a stronger attraction between the nucleus and the electrons in the orbitals so the electrons are pulled inwards towards the nucleus. This contracts the radius inwards and therefore the atomic radius decreases.
The melting point of the elements across a period changes according to their structure. Both structure and bonding have an effect on the melting point of an element as we learned earlier in the book.
We will now discuss the trend in melting points across Period 3:
1. The change in melting point from Sodium to Aluminium Na to Al.
Sodium, magnesium and aluminium are all metals and therefore have metallic bonding.
As well learned earlier, the more delocalised electrons present and the smaller the radius of the atom, the higher the melting point of the metal.
As we move across period 3 the number of delocalised electrons per metal atom increases and the radius of the elements decreases. This means the melting point increases.
This is because there is a greater electrostatic attraction between the positive ions and delocalised electrons and hence the metallic bond is stronger and requires more energy to break.
2. The melting point of Silicon Si
Silicon has a macromolecular structure which consists of covalent bonding.
As we learned earlier, macromolecular structures have strong covalent bonds that hold the atoms together.
These strong covalent bonds require a large amount of energy to break and therefore silicon has a high melting point.
3. The change in melting point from Phosphorous to Chlorine P to Cl
Phosphorous P4, sulfur S8 and chlorine Cl2 are simple molecular substances which consist of van der Waals forces.
As learned earlier, van der Waals forces are weak intermolecular forces which require a small amount of energy to break. For this reason, the melting points of these simple molecular substances are low.
The melting point of these substance depends on the varying strength of van der Waals forces. The shape of a molecule and the distance between the molecules affects the strength of induced dipole-dipole forces.
The stronger the induced dipole-dipole forces, the higher the melting point. A larger molecule contains more electrons, therefore it consists of larger electron clouds. The greater the number of electron clouds, the stronger the induced dipole-dipole forces. More energy is required to break stronger induced dipole-dipole forces, therefore the melting point is higher.
As sulfur is the largest molecule out of the three, it contains the most number of electrons and the strongest van der Waals forces. Therefore sulfur has the highest melting point, compared to phosphorous and chlorine.
4. The melting point of Argon Ar
Argon is a noble gas and has a very low melting point as it exists as a monoatomic element consisting of very weak van der Waals forces.
As the van der Waals forces in argon are weak, a very small amount of energy is needed to break them and therefore the melting point is low.
Electrical conductivity increases across metals. Sodium, magnesium and aluminum all exist as giant metallic lattices and hence are able to conduct electricity. As you move along the period, the number of mobile electrons donated by each atom into the sea of delocalised electrons increases so that the metal becomes better at conducting electricity.
🔓 Unlock Full Chemistry Course: https://courses.medicmind.co.uk/p/ale...
🔓 Unlock Full Biology Course: https://courses.medicmind.co.uk/p/aqa...
🔖 Past Papers: https://www.studymind.co.uk/resources/
👩🏻🏫 Chemistry 1-1 Tutoring: https://www.studymind.co.uk/subject/a...
👩🏻🏫 Biology 1-1 Tutoring: https://www.studymind.co.uk/subject/a...
#ALevelChemistry #ALevelBiology #Biology #Chemistry #StudyMind