3. Periodicity

Question 1

Periodic Trends - Atomic Radii

Answer 1

• Decreases across a period
  
  • nuclear charge increases, while the electrons remain on the same valence shell
• Increases down a group
  
  • Even though the nuclear charge is increasing, there are more electrons, which result in more electron shielding

Question 2

Periodic Trends - Ionic Radii

Answer 2

• Cations get smaller
  
  • They lose their valence e^-, thus the remaining electrons are pulled tighter to the nucleus
• Anions get larger
  
  • Electron shielding weakens the force between electrons and the nucleus

Question 3

Periodic Trends - Ionization Energy

Answer 3

• Increases across a period
  
  • nuclear charge is increasing despite the increase in electrons
• Decreases down a group
  
  • electrons are further away from the nucleus in addition to electron shielding

Question 4

Periodic Trends - Electronegativity

Answer 4

A measure of the ability of an atom to attract bonded electron pairs to itself when in a covalent bond

• Metals have small electronegativity values
• Nonmetals have higher electronegativity values

Question 5

Periodic Trends - Electron Affinity

Answer 5

The energy released when 1 mol of electrons is attached to 1 mol of neutral atoms or molecules in the gas phase

• same increase/ decrease as Ionization Energy

Question 6

Group 1 - Alkali Metal properties

Answer 6

• Low melting / boiling points
  
  • decreases down the group –> increase in shielding and less nuclear shielding
• Very reactive
  
  • needs to lose only one electron to have a full shell
• Large atoms
  
  • metals are soft and not dense

Question 7

Group 1 - Alkali Metal reactions

_{(with water and halogens)}

Answer 7

With water:

• React vigorously with water to create a hydrogen and a base
  
  • Na_(s) + H₂O_(l) –> NaOH_(aq) +H_2(g)

With halogens:

• React vigorously with halogens to form salts
  
  • 2Na_(s) + Cl_2(g) –> 2NaCl_(s)

Question 8

Group 17 - Halogen properties

Answer 8

• Very reactive / electronegative
  
  • Needs to gain just one electron to have a full valence shell
• High melting / boiling points
  
  • Increases down the group –> increased LDF between the simple covalent molecules and increased molecular weight
• Down the group
  
  • becomes darker
  • decreases in reactivity
    
    • A halogen higher up the group will displace the one lower down

Question 9

Oxide Reactions and pH

Answer 9

• Oxides of elements have increasing acidity across a period
  
  • Al is amphoteric
• Metal oxides are basic
• Nonmetal oxides are acidic

Question 10

Transition Element (definition)

Answer 10

An element that possesses an incomplete d-sublevel in one or more oxidation states

_{zinc is not a transition element because it has a full d-sublevel in its atoms/ ions}

Transition elements have an empty d orbital - the d orbitals splits into 2 energy sublevels and electrons moving between these gives them their properties

• Cu / Cr - it is more energetically favorable to half-fill and completely fill the d sublevel, so they only contain one 4s e^-

Question 11

Properties of Transition Metals

Answer 11

• produces colors and allows for complex ion formation
• variable oxidation numbers - good catalysts
• when transition metals lose electrons, they lose the 4s first
• all transition metals have an oxidation state of +2
  
  • occurs when they lose both s orbital e^-s
• most transition metals are diamagnetic (repelled)
  
  • only a few are paramagnetic due to unpaired electrons allowing spin in one direction to form poles

Question 12

Ligands

Answer 12

A neutral molecule / anion which contains a non-bonding pair of electrons, these form coordinate bonds with the metal ion to form complex ions - donates a pair of electrons to a central metal ion to form a covalent bond

Question 13

Complex ions

Answer 13

Consists of a central atom, which is usually a metal atom/ ion and attached ligands

Coordination number: the total number of points at which a central atom / ions attaches ligands

• 2 - linear
• 4 - square planar / tetrahedral
• 8 - octahedral

The charge on a complex ion is the sum of the charges of the metal ion and the ligands

Question 14

Colored Complexes

Answer 14

Transition metal ions are colored due to the d-d electron transitions between d orbitals which are split in the electric field due to the presence of ligands

• color obvserved is complementary to the color absorbed
• ions with higher charge and ligands with greater charge density produce a greater split in the d orbitals
• polydentate ligands form more than one coordinate bond with the metal ion