2.1 Periodicity

Question 1

What is meant by the term periodicity?

Answer 1

Periodicity is the repeating pattern of physical or chemical properties going across the periods

Question 2

Draw/Describe a periodic table highlighting the classification of elements in s,p,d blocks

Question 3

What happens to atomic radii across a period?

Answer 3

Atomic radii decrease from left to right across a period, because the increased number of protons create more positive charge attraction for electrons which are in the same shell with similar shielding.

Question 3

What is the general tend in first ionisation across a period?

Answer 3

There is a general trend across to increase. This is due to increasing number of protons as the electrons are being added to the same shell.

Question 4

Why is there a drop in 1st ionisation energy from Mg to Al

Answer 4

There is a small drop between Mg + Al. Mg has its outer electrons in the 3s sub shell, whereas Al is starting to fill the 3p subshell. Al’s electron is slightly easier to remove because the 3p electrons are higher in energy.

Question 5

Why is there a small drop between phosphorous and sulfur?

Answer 5

Sulfur’s outer electron is being paired up with another electron in the same 3p orbital.
When the second electron is added to an orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove.

Question 6

What is the trend in melting point for Na, Mg, Al?

Answer 6

Metallic bonding : strong bonding – gets stronger the more electrons there are in the outer shell that are released to the sea of electrons. A smaller sized ion with a greater positive charge also makes the bonding stronger. Higher energy is needed to break bonds.

Question 7

Why does Si have the highest melting point?

Answer 7

Si is Macromolecular: many strong covalent bonds between atoms, high energy needed to break covalent bonds– very high mp +bp

Question 8

Why does the melting point fall from Si to Cl2?

Answer 8

Cl2 (g), S8 (s), P4 (S)- simple molecular: weak van der Waals between molecules, so little energy is needed to break them – low mp+ bp.

Question 9

Why does S8 have a higher mp than P4

Answer 9

has a higher mp than P4 because it has more electrons so has stronger van der Waals between molecules and hence higher mp

Question 10

Why does Ar have the lowest mp?

Answer 10

monoatomic weak van der waals between atoms- only exist as an individual atom. has smaller van der Waals forces hence lower mp/bp