The Periodic Table Flashcards
What is periodicity?
The trends in physical and chemical properties of elements as you go across the periodic table.
How does melting and boiling points vary across a period for metals?
They increase across the period because the metal-metal bonds get stronger.
This is because the metal ions have a greater charge, an increasing number of delocalised electrons and a decreasing ionic radius.
This leads to a higher charge density, which attracts the ions together more strongly.
Why do elements such as carbon, diamond and silicon have high melting and boiling points?
They are elements with macromolecular structures which have strong covalent bonds linking all their atoms together.
A lot of energy is needed to break these bonds.
What does the melting and boiling points of simple molecular substances depend on?
The strength of the Van der Waals forces.
Why do simple molecular substances have low melting and boiling points?
Van der Waals forces are weak and easily overcome so these elements have low melting and boiling points.
How does atomic radius vary across a period?
It decreases across a period.
As the number of protons increases, the positive change of the nucleus increases and this means electrons are pulled closer to the nucleus making the radius smaller.
What is the trend in ionisation energy across a period?
The general trend is for the ionisation energies to increase.
The number of protons is increasing- stronger nuclear attraction.
All the electrons are at roughly the same energy level- little extra shielding.
What is the trend in ionisation energy down a group?
The general trend is for the ionisation energies to decrease.
Elements further down a group have extra electron shells compared to ones above.
Extra shells mean that the outer electrons are further from the nucleus.
More shielding occurs.
Why is it that as you go across period 3, boiling point generally increases?
As you move from Na to Al the metal ions have an increasing number of delocalised electrons.
This means that the metallic bonds are stronger- so more energy is required to break the bonds and boil the metal.
Explain why Si has the highest boiling point of all the Period 3 elements.
Si has a giant, macromolecular structure with strong covalent bonds holding the atoms together.
Lots of energy is required to break these bonds so the boiling point of Si is extremely high.
Explain why the boiling point of sulfur is higher than that of chlorine.
Sulfur forms larger molecules than chlorine, so its molecules have more electrons.
So the van der Waals forces holding the sulfur molecules together are stronger.
So more energy is required to break the bonds and the boiling point is higher.
