Chapter 7- Periodicity

Question 1

how did Mendeleev order the periodic table

Answer 1

by atomic mass - he left gaps where required so that elements could be in groups of similar chemical properties

Question 2

what happens to atomic number moving left to right

Answer 2

it increases

Question 3

what are groups

Answer 3

elements with the same chemical properties because they have the same number of outer electrons

Question 4

what are periods

Answer 4

horizontal rows, period number relates to the highest energy level held by electrons in that atom

Question 5

what does periodicity include

Answer 5

• electron configuration
• ionisation energy
• structure
• melting/boiling points

Question 6

what are the blocks of the periodic table

Answer 6

+ s-block = groups 1 and 2 –> outermost electrons in the s-subshell
+ d-block = transition metals - outer electrons in d subshell
+ p-block = right side = outermost electrons in the P subshell

Question 7

what is the definition of ionisation energy

Answer 7

“the energy required to remove one electron from each atom in one mole of gaseous atoms”

Question 8

what are the 3 factors affecting ionisation energy

Answer 8

nuclear charge, atomic radius, shielding

MENTION ALL 3 IN ANSWERS

Question 9

explanation of how nuclear charge affects ionisation energy

Answer 9

the greater the atomic number/nuclear charge, the more protons there are; this exerts a greater pull on the outer electrons / more electrostatic forces, so more energy is required to remove the outer electron

Question 10

explanation of how atomic radius affects ionisation energy

Answer 10

a greater atomic radius leaves the outer electrons further from the nucleus, across a period atomic radius decreases due to increased nuclear charge, a greater distance gives less electrostatic force so less ionisation energy

Question 11

explanation of how shielding affects ionisation energy

Answer 11

greater shielding reduces the attraction from the nucleus to the outer electrons, this decreases ionisation energy. so more electron shells gives a lower ionisation energy

Question 12

what happens to ionisation energy across a period

Answer 12

• nuclear charge increases across a period so electrostatic attraction increases
• atomic radius decreases across a period due to greater nuclear charge. this means the outer electrons are closer to the nucleus so attraction increases
• shielding remains constant
• overall ionisation energy increases

Question 13

what are the two exceptions to the general ionisation energy rule across a period

Answer 13

• where a higher energy subshell is being filled/electron being removed from; this is further away so ionisation energy decreases
• paired electrons in P subshell are easier to remove due to the repulsion between electrons (only for first paired p electron)

Question 14

explanation of ionisation energy down a group

Answer 14

• shielding increases as you move down a group; this decreases attraction to outer electrons
• atomic radius increases down a group; this decreases electrostatic attraction to outer electrons
• nuclear charge increases down a group but this is not sufficient to overcome the changes due to the other factors
• overall ionisation energy decreases

Question 15

how does energy change with successive ionisations

Answer 15

• with each successive ionisation, more energy is required as you are then removing an electron from a positive ion
• this increases the effective nuclear charge

Question 16

what does a ‘big jump’ indicate in successive ionisation energies

Answer 16

that a new shell has been entered

Question 17

what is metallic bonding

Answer 17

metallic bonding occurs when metal atoms ‘donate’ their outer electrons to form positive ions in a sea of delocalised electrons.
the cations are fixed, the electrons are not

Question 18

what are the properties of metallic substances

Answer 18

most are:

• strong due to large electrostatic forces
• high electrical conductivity- the electrons are free to move a charge
• high mpt and bpt; ‘a large amount of energy is required to overcome the strong electrostatic forces in metallic bonding’
• insoluble

Question 19

what is one factor of a metal’s bpt

Answer 19

• the ion that it forms, 1+, 2+ etc.

Question 20

giant covalent structures examples

Answer 20

boron, carbon, silicon

Question 21

what are some properties of giant covalent structures

Answer 21

• very high mpt and bpt because a large amount of energy is required to break covalent bonds
• almost completely insoluble
• don’t conduct electricity (other than graphite and graphene)

Question 22

why do group 2 metals have a higher bpt and mpt than group 1 metals

Answer 22

they donate 2 electrons not 1 so there are greater electrostatic forces

Question 23

mpt and bpt trends across periods 2 and 3

Answer 23

• increases G1 to G2 and aluminium is higher again
• bpts max at carbon and silicon because covalently bonded
• tends to decrease after this because only intermolecular forces need to be broken

Question 24

what is an exception of bpts decreasing after carbon and silcon

Answer 24

sulphur has a higher bpt than phosphorus because it is S8 but only P4 so there are greater London forces

Question 25

Why is the hydrogen bonding stronger in water than in ammonia (2)

Answer 25

• water has two lone pairs so it can form twice as many hydrogen bonds
• O-H is a greater dipole than N-H so it has a greater electrostatic attraction

Question 26

if there is a large jump between the Xth and (X+1)th ionisation energies, which position in the period does the element sit

Answer 26

the Xth position

- if there is a large jump at 5–> 6 for example then the element must have 5 in its outer shell

Question 27

ideally how should you write the electron configurations

Answer 27

in order of numbers so 3d before 4s even though 4s fills first, doesn’t really matter though

Question 28

which things should always be mentioned when comparing the atomic radius of elements in the same period

Answer 28

• nuclear charge and therefore electrostatic attraction

- SAME NUMBER OF SHELLS