Chapter 7 - Periodicity

Question 1

who came up with the periodic table and what did they do?

Answer 1

• Mendeleev - arranged in increasing atomic mass
• lined up elements in groups w/ similar properties
• if properties didn’t fit he would swap them e.g. I & Te
• left gaps for elements not discovered yet

Question 2

how is the periodic table arranged

Answer 2

• increasing atomic no.
• metals vs non-metals - staircase under boron
• groups - similar chemical properties and same no. of electrons in outer shell
• horizontal rows - periods

Question 3

metalloids

Answer 3

• B
• Si
• Ge
• As
• Sb
• Te
• At

Question 4

periodicity

Answer 4

repeating trend in properties of elements across periods

Question 5

periodicity examples

Answer 5

• electron configuration
• ionisation energy
• structure
• melting points

Question 6

trends across periods (electron config.)

Answer 6

s-sub shell fills then p sub-shell

Question 7

blocks of periodic table

Answer 7

• corresponds to highest energy shell:
  s-block –> grp 1&2
  p-block –> grp 13-18
  d-block –> grp 3-12
  f-block –> lanthanides & acintides

Question 8

what’s ionisation energy

Answer 8

• measures how easily an atom loses it’s electrons to form positive ions

Question 9

first ionisation energy definition

Answer 9

energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous +1 ions

Question 10

factors affecting ionisation energy

Answer 10

• atomic radius - as it increases. attraction decreases
• nuclear charge - more protons they are, the greater the attraction
• electron shielding - inner-shells repel - larger the atom, the more shielding, the less attraction

Question 11

second ionisation energy

Answer 11

energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous +2 ions

Question 12

trend in successive ionisation energy

Answer 12

• it increases each time as each time an electron is removed, nuclear charge attracted to less electrons
• large increase suggests it’s moved to inner shell - decrease in radius

Question 13

trend in ionisation energy down a group

Answer 13

decreases, radius and shielding increases, attraction decreases so ionisation energy does

Question 14

trend in ionisation energy across a period

Answer 14

nuclear charge increases as well as attraction, atomic radius decreases so ionisation energy increases

Question 15

why is there a fall in ionisation energy between Be & B

Answer 15

Be fills the 2s sub-shell, B fills 2s & one 2p, this is more unstable so it loses an electron more easily, so lower ionisation energy

Question 16

why is there a fall in ionisation energy between N & O

Answer 16

N has one electron in each 2p sub-shell
O has one 2p sub-shell w/ 2 electrons, the other 2 having one electron, this is more unstable so it loses an electron more easily, so lower ionisation energy

Question 17

Metallic bonding & structure

Answer 17

electrostatic attraction between the cations and delocalised electrons
- cations in fixed position, delocalised electrons are free to move around - forms giant metallic lattice

Question 18

properties of metals

Answer 18

• electrical conductivity - due to delocalised electrons
• strong metallic bonds - more delocalised electrons, stronger the bonds
• high m.p/b.p - depends on strength of bonds, high due to lots of energy needed to overcome strong electrostatic attraction between electrons and cations
• are not soluble

Question 19

Giant covalent structures

Answer 19

many atoms hold together by a network of strong covalent bonds

Question 20

properties of giant covalent structures

Answer 20

• high m.p/b.p - lots of energy needed to overcome strong covalent bonds
• insoluble as bonds are too strong to be broken by interactions with lattices
• don’t usually conduct electricity - no delocalised electrons

Question 21

graphite

Answer 21

• parallel layers of hexagonally attracted C atoms, have 3 bonds, so delocalised electrons
• weak intermolecular forces between layers
• can conduct electricity

Question 22

graphene

Answer 22

• one layer of graphite
• can also conduct electricity

Question 23

melting point trends across periods

Answer 23

• increases as metallic bonds gets stronger
• continues to increase as it reaches giant covalent structures
• then has a large decrease when gets to simple molecules

Question 24

structure trends across periods

Answer 24

• first giant metallic
• then giant covalent
• then simple molecular