3.2 Inorganic Chemistry: .1 Periodicity

Question 1

what is meant by periodicity?

Answer 1

trends that occur (in physical and chemical properties) as you move across the periods.

Question 2

what is the trend in atomic radius as you go across the period?

Answer 2

-as the number of protons increases , the positive charge of the nucleus increases. This means that the electrons are pulled closer to the nucleus, making the atomic radius smaller.

Question 3

why does the extra electrons that the elements gain across a period not affect the atomic radius?

Answer 3

-the extra electrons that the elements gain across a period are added to the outer energy level -so they don’t really provide any extra shielding effect

Question 4

what is the trend in atomic radius as you down the group?

Answer 4

-as you go down the group the atomic radius increases down the group -the atoms of each element have one extra complete main level of electrons compared with the one before

Question 5

what is the trend in melting point as you go across a period 3 metals ?

Answer 5

-the melting points and boiling points increase from sodium and aluminium -because the strength of the metallic bond increases. -this is due to the fact that as you go across the metal ions have an increasing positive charge, an increasing number of delocalised electrons and decreasing radius

Question 6

why does sodium have a higher melting point than magnesium?

Answer 6

-

Question 7

in the trend in melting and boiling points of the period 3 elements why does silicon have a high melting and boiling point?

Answer 7

-silicon is macromolecular with a tetrahedral structure -strong covalent bonds link all the atoms together -a lot of energy is needed to break these bonds -so silicon has a high melting point

Question 8

in the trend in melting and boiling points of the period 3 elements why are the melting and boiling points of P, S and Cl low? why does sulphur have the highest melting/boiling point out of these 3 elements?

Answer 8

-P, S, Cl all have simple covalent (molecular) structures -there melting points are due to the strength of the Van der Waals forces between the molecules. -Van der Waals forces are weak and easily overcome so these elements have low melting points. Sulphur is the biggest molecule (S8) so its got a highest melting point

Question 9

explain why phosphorus has a higher melting point than Chlorine?

Answer 9

-The phosphorus molecule contains P4 molecule -whilst the Chlorine molecule has the Cl2 molecule -therefore Phosphorus is bigger molecule than Chlorine -more atoms in a molecule mean stronger Van der Waal forces -Phosphorus has stronger Van der Waal forces than Chlorine molecule -so more energy is required to overcome the Van der Waal forces -hence the a higher melting point is needed

Question 10

out of P, S, Cl and Ar why does argon have the lowest melting point?

Answer 10

-argon is molecules are just single argon atoms -it is monatomic -resulting in very week Van der Waals -that don’t need a lot of energy to overcome

Question 11

which block is Sodium in?

Answer 11

the s-block

Question 12

which block is rhodium in?

Answer 12

the d-block

Question 13

which block is iodine in?

Answer 13

the p-block

Question 14

which block is Curium in?

Answer 14

the f-block

Question 15

what do you call the elements in group 1?

Answer 15

the alkali metals

Question 16

what do you call the elements in group 2?

Answer 16

the alkaline earth metals

Question 17

what do you call the element in the d-block

Answer 17

the transition metals

Question 18

what do you call the elements in group 7?

Answer 18

the halogens

Question 19

what is meant by first ionisation energy and give the equation for the first ionisation energy of Mg?

Answer 19

-the first ionisation energy is the energy required to convert a mole of a gaseous atoms into a mole of single positively charged gaseous ions (the energy required to remove one electron from each atom) -Mg (g) –> M+ (g) +e-(g)

Question 20

what is the general trend in ionisation energy as you go across a period?

Answer 20

the first ionisation energy generally increases across a period

Question 21

why does the first ionisation energy increase across a period?

Answer 21

• as you go across a period from left to right the number of protons in the nucleus increases,
• which means a stronger nuclear attraction
• all the extra electrons are at roughly the same energy level even if the outer electrons are in different orbital types
• this means theres a generally little extra shielding effect or extra distance to lessen the attraction from the nucleus

Question 22

what is the pattern for the increase in ionisation energy across a period

Answer 22

2,3,3

Question 23

why does the ionisation energy drop between phosphorus and Sulphur?

Answer 23

• if you look at the electron congiuration of phosporus you will see that it has 3 electrons in the p sub shell (orbitals) whlist sulphur has one more electron so it must pair up in the p orbital
• this means in sulphur there is spin pairing in the p orbital
• this paired up electrons have a greater repulsion which means that not as much energy is required to remove the outer electron
• hence a decrease in ionisaition energy

Question 24

why is there a drop in ionisation in period 3 for aluminium?

Answer 24

-the shielding is identical in these elements so it does not a factor in ionisaition energy

if you look at the electron configuration for magnesium and aluminium you will see that aluminium’s outer electron is in a 3p orbital rather than a 3s.

-the 3p has a slighly higher energy than the 3s orbital mean not as much energy is required to remove the electron and is further away from the nucleus which means that the

Question 25

what is the general trend for ionisation energy down a group?

Answer 25

it generally decreases down a group

Question 26

why does the ionisation energy generally decrease down a group?

Answer 26

• as you go down the group the amount of shells in each atom increases
• this means that the outer electron is more shielded from the nucleus
• this means that the nuclear attraction is weaker
• meaning that less energy is required to take the outer electron from the atom

Question 27

the values 906, 1763, 14 855 and 21 013 kJ mol-1 are the first 4 successive ionisaiton energies of an element

state which group this element is in and why

Answer 27

this element is in group 2 because the big jump occurs after two electrons have been removed.