The Periodic Table and Periodicity

Question 1

what groups in the periodic table are in the s-block

Answer 1

group 1 and 2

Question 2

what groups in the periodic table are in the p-block

Answer 2

group 3 to 8

Question 3

what groups in the periodic table are in the d-block

Answer 3

the transition metals (3 to 13 in a group 1 to 18 periodic table)

Question 4

what is the general trend in the blocks as you go across them and why does the number of groups each block occupies make sense

Answer 4

• there is one more electron in the outer shell for every group you go across (left to right)
• this makes sense as the s orbital can only hold 2 electrons
• so the s-block stops at group 1 and 2 which consist of an s orbital in their outer shells
• the p-block consists of 6 groups
• which matches with the 6 electrons a p subshell can hold with 3 p orbitals
• the d subshell that has 5 d orbitals can hold 10 electrons
• which matches with the ten ‘groups’ the d-block encompasses (the transition metals)

Question 5

if the periodic table has the s-block on the left, d-block in the middle and p-block on the right, what does that imply about the actual order or arrangement of the periodic table

Answer 5

• that the table is divided into blocks

- rather than simply groups and periods

Question 6

what is the definition of peridicity

Answer 6

• the regularly repeating pattern
• of atomic, physical and chemical properties
• with increasing atomic mass

Question 7

what is the atomic radius of an element

Answer 7

• the measure of the size of its atoms

- measured by the distance from the centre of the nucleus to the boundary of the electron cloud

Question 8

since the atom doesnt have a well defined boundary, how is the atomic radius of an atom practically calculated

Answer 8

• by determining the distance between two nuclei

- and dividing it by 2

Question 9

what is the covelant radius of an atom

Answer 9

the radius of the atom when it is covelantly bonded with another atom

Question 10

why are the covelant radii and atomic radii different, even for the same atom of the same element

Answer 10

• when measuring the atomic radii practically, the boundaries of the two atoms would only be touching and not overlapping
• this means that the distance between the two nuclei can be measured (diameter)
• which would give you the radius of the atom
• but for a covelantly bonded atom the boundaries of the electron clouds are overlapping
• which means that the distance between the two nuclei (the diameter) would be decreased

Question 11

why are the boundaries of the electron clouds overlapping for the covelantly bonded atoms whereas they are only touching for the other example

Answer 11

• because covelant bonding consists of the sharing of electrons
• so their outer shells would have to overlap to do this
• whereas for the atomic example, there is no bond
• so the outer shells dont interact with each other, they would more likely repel

Question 12

which one between the covelant radius and atomic radius is usually shorter and why

Answer 12

• the covelant radius
• because the boundaries of their electrons clouds are overlapping
• which means that the measured distance between the nuclei is smaller
• leading to a smaller radius

Question 13

what is the real name of the radius that can only be determined for group 8 elements (other than calling it the atomic radius)

Answer 13

the van der Waals radius

Question 14

why can only one type of radius be determined for the group 8 elements

Answer 14

• because they dont bond with other elements voluntarily

- so they can only have a ven der waals radius and not a covelant radius

Question 15

what is the third radius called and what is it used for

Answer 15

• the metallic radius

- which is used for metals

Question 16

how does the atomic radii generally change across periods

Answer 16

the atomic radii decreases

Question 17

how does the nuclear charge change across the period and what is its effect

Answer 17

• the nuclear charge increases due to the increase in protons in the nucleus
• this leads to stronger electrostatic forces of attraction between the nucleus and the electrons which pulls them closer towards each other
• causing the atomic radius to decrease

Question 18

how does the electron-electron repulsion change and what effect does this lead to

Answer 18

• the number of electrons in the same quantum shell increases
• which leads to an increased shielding effect that repels the electrons away from each other
• causing the atomic radius to increase

Question 19

which changing factor proves to be more significant

Answer 19

• the increase in the nuclear charge

- which causes the overall atomic radius to decrease across the periods

Question 20

the electronic configuration of Be is 1s2 2s2 whereas for B it is 1s2 2s2 2p1. knowing that these elements are in the first group and there should be a general increase in the first ionisation energies across a period, why is the first ionisation energy of B lower than that of Be if it has a larger nuclear charge

Answer 20

• the boron atom has one electron in the 2p orbital meaning it is sitting at a higher energy level than the electrons in the 2s orbital
• this means that less energy would be required in order to remove the electron
• also, there is an increased effect of shielding experienced by the electron due to there being two inner subshells rather than just the one Be has
• which leads to it having even more energy
• which leads to a lower ionisaton energy being required

Question 21

N has an e.c. of 1s2, 2s2, 2p1, 2p1, 2p1
O hasan e.c. of 1s2, 2s2, 2p2, 2p1, 2p1
which element would have the lower first ionisation energy and why

Answer 21

• the oxygen
• because one of the electrons in the 2 p orbital that is full would be preferred to be removed first
• the electron in this orbital experiences electron-electron repulsion from the other electron in its orbital
• due to this the electron has a higher energy level
• so the first ionisation energy would be less than nitrogen’s

Question 22

why would one of the electrons in the 2 p orbital that is full be preferred to be removed first

Answer 22

• because the atom would simply prefer to have an equal share of electrons across the 3 p orbitals (2p1, 2p1, 2p1)
• than having it as 2p2, 2p1, 2p0
• as the pair of electrons in the p orbital already have higher energy levels

Question 23

if energy has to be supplied to the oxygen or boron atom in order for the electron to be removed, what does this imply about the energy levels of the ion

Answer 23

that the ion is energetically less stable than the atom