3.1.1 Periodicity

Question 1

How are elements arranged in the periodic table (periods)?

Answer 1

• horizontal rows
• elements show gradual changes (trends) in properties across the period
• trends are repeated across each period and the repeated pattern of trends is called periodicity

Question 2

How are elements arranged by atomic number?

Answer 2

Arranged in order of increasing atomic number starting with hydrogen

Question 3

How are elements arranged (groups)?

Answer 3

• patterns in (similar) chemical and physical properties
• all have the same number of electrons in the outer shell and the same type of orbitals

Question 4

What is the periodic trend in period 2 and 3?

Answer 4

Metals to non-metals
Solids to gases or low melting solids
Melting and boiling points increase
They remain high for giant covalent structures and fall for simple molecular structures
Metallic bonds become stronger across the group as there is an increased attraction between the positive metal ion and the sea of delocalised electrons
Number of electrons in the outer shell increases in proportion to the increasing charge on the metal ions

Question 5

How are elements classified into s-, p- and d- blocks?

Answer 5

• periodic table is structured into blocks that are linked to sub-shells
• this pattern mirrors the subshells that are being filled

Question 6

How does ionisation energy change down a group?

Answer 6

the atomic radius increases, electron shielding increases and both of these outweigh the effect of the increased nuclear charge. this means its easier to lose an electron and ionisation will decrease.

Question 7

How does ionisation energy change across a period?

Answer 7

the nuclear charge increases so there’s a greater attraction from the nucleus for the outer shell electrons. the increased nuclear charge pulls electron shells closer together so atomic radius decreases. electron shielding remains the same as no more shells are added. this makes it harder to lose an outer-shell electron and so ionisation energy increases.

Question 8

describe the anomaly in first ionisation energy in elements between 2s and 2p (also applies to 3s and 3p)

Answer 8

there’s a drop in ionisation energy between Be and B. Boron marks the filling of the 2p sub shell which has a higher energy level than the 2s sub shell in Be.
therefore, it is easier to remove 1 electron from the 2p sub shell in boron than the 2s sub shell in beryllium.

Question 9

explain the anomaly in ionisation energy between N and O. or P and S

Answer 9

there’s a drop in ionisation energy between nitrogen and oxygen as oxygen marks the beginning of electron pairing in the 2p orbitals.
the two electron in the first orbital of 2p repel each other making it easier to lose and electron.

Question 10

what does a increasing ionisation energy of an atom show

Answer 10

ionisation energy of an atom show
it shows its getting harder to remove electrons. electrons with larger ionisation energies are closer to the nucleus.

Question 11

Explain trends in melting point

Answer 11

Dependant on structure and bond type
- decreases down groups
- metallic bonding decreases as size increases
- electron cloud isn’t as effective at holding ions together
- variable across groups
- rises as metals contribute more to the electron cloud
- big rise for giant molecules in group 4
- drops for simple molecules with weak IM forces