Theory

Question 1

What are isotopes?

Answer 1

• different atoms of the same element
• same number of p+, different n0
• physical properties differ

Question 2

What are the exceptions in electronic configuration?

Answer 2

• Cu-29
  
  • full-filled d orbital
    
    • high symmetry, energetically more stable
• Cr-24
  
  • half-filled d orbital

Question 3

How are transitions metal cations formed?

Answer 3

• e- from 4s orbital lost first → then d
• d orbital higher energy → difficult to remove

Question 4

What are the steps in mass spectrum?

Answer 4

1. vaporisation
   
   • liquid / solid → gas
   • low pressure
2. ionisation
   
   • atoms → cations
     
     • fast moving e-
3. acceleration of cations in electric field
4. deflection in magnetic field → depends on m/z
5. detection
   
   • cations registered according to m/z value
   • y-axis = abundance of each value

Question 5

What are the components of electromagnetic spectrum?

Answer 5

• gamma rays → shortest wavelength = highest energy
• X rays
• UV radiation
• VIS radiation
• IR radiation
• microwaves
• radiowaves

Question 6

What is the difference between line and continuous spectrum?

Answer 6

• continuous
  
  • all frequencies
  • white light through prim → all colours visible
• line spectrum
  
  • discrete lines → unique
  • characteristic for each element

Question 7

What is hydrogen emission spectrum?

Answer 7

• H placed in spectroscope
  
  • energy applied → e- excited → move to higher energy level
  • falling to lower energy registered on spectrum
    
    • photon of light given out
• higher (potential) energy levels → converging
  
  • lines on spectrum → also converge as energy increases
  • lines → e- in energy levels
    
    • e- in atom have certain amount of energy

Question 8

How can ionisation energy be deduced from hydrogen emission spectrum?

Answer 8

• energy levels converge
• H has 1e- → lowest energy level
  
  • energy to infinite level → removed from atom (H+)
• falling back → same energy

Question 9

What is ionisation energy?

Answer 9

• energy required to remove 1e- from gaseous atom to form 1 mol of positively charged ions
• successive IE
  
  • new main energy level → harder
    
    • closer to nucleus
    • shielded by fewer e-
      
      • shielding = electrons in between
  • larger diff. between sub-levels → 3p higher energy, less energy to remove e-

Question 10

How does IE change in periodic table?

Answer 10

• same period
  
  • increase with atomic number → nuclear charge
  • same main energy → same shielding

Hund’s rule: orbitals of the same sub-level are occupied by single electrons firstly then pairs are formed

• e- in the same p orbital as another → repulsion → easy to remove
• exemptions (according to Hund)
  
  • IE(P) > IE(S), Mg and Al, N and O, Be and B
  • half-filled / full-filled orbitals → high symmetry and stable
    
    • more energy needed to remove e-
• same group → decreases (top to bottom)
  
  • e- further from nucleus

Question 11

What is the source of colour of flames (when compounds are burnt) and on what does the colour depend on?

Answer 11

• promoted e- fall back to lower energy levels
  
  • heat = energy → absorbed by e-
• differs for molecules because: energy difference varies between levels
  
  • different nuclear charge

Question 12

On what does density of an element depend?

Answer 12

• atomic mass
• metallic bonding (the stronger the greater density)
  
  • smaller radius
• number of electrons per atom delocalised
  
  • the greater the higher density

Question 13

Why is C–N bond shorter in urea than other compounds?

Answer 13

• lone pair of e- (on N) is delocalised over the whole molecule
• lone pair of e- donated to C–N bond
• slight positive charge on C (C=O bonding) → induced dipole
  
  • greater attraction

Question 14

How does atomic and ionic radius change across the periodic table?

Answer 14

• atomic radius
  
  • increases down the group → number of shells increases
  • decreases across period → p+ increases
• ionic radius
  
  • cations (+) → smaller than mother atom
    
    • less e- (or shells) → less repulsion
  • anions (-) → larger
    - more e-

Question 15

How does electronegativity change across the periodic table?

Answer 15

• electronegativity = measure of atom attraction in a molecule for e- pair in covalent bond
• Cs lowest, F highest
• decreases down group
  
  • more shells → bonding pair further from nucleus
  • higher nuclear charge balanced by shielding
• increases across period
  
  • nuclear charge increases

Question 16

How does electron affinity change across periodic table?

Answer 16

• electron affinity = enthalpy change when 1e- is added to each atom in 1 mol of gaseous atoms under standard conditions
• 17th group → decreases down (more exothermic)
  
  • Cl most exo-
  • bigger atom → e- less attracted
• across period (13 → 17 gr)
  
  • more exothermic → nuclear charge increases
  • smaller radius

Question 17

How does melting point change across periodic table?

Answer 17

• metallic bonding
  
  • lattice of metal cations surrounded by sea of delocalised e-
  • decreases down group
    
    • deloc. e- less attracted → increase in shells
  • increases across period (Na, Mg, Al)
    
    • charge of cations increases → deloc. e- more attracted
• non metals → covalent bonding
  
  • increases down the group
    
    • London forces → prop. to relative mol. mass

Question 18

What are the properties of oxides from 3rd period?

Answer 18

• ionic: Na, Mg
  
  • basic
• between ionic and covalent: Al
  
  • amphoteric
• giant covalent: Si
  
  • SiO neutral, SiO2 acidic
• molecular covalent: P, S, Cl
  
  • acidic

Question 19

Why do transition metals have more than 1 oxidation number?

Answer 19

• no big jump in ionisation energy between 4s and 3d
• depends on: lattice and hydration enthalpy

Question 20

What is entropy?

Answer 20

• measure of disorder (the more the higher the entropy)
• highest for gases

Question 21

Explain magnetic properties of transition metals

Answer 21

• ferromagnetism
  
  • permanent
  • e- align → each domain has the same charge
  • Fe, Co, Ni
• paramagnetic
  
  • unpaired e- spin
    
    • magnetic field applied → line up
  • Hund’s rule → many cations
• diamagnetic
  
  • paired e-
  • repulsed in external magnetic field

Question 22

Examples of transition metal catalysts in reactions

Answer 22

• Haber process: Fe
  
  • heterogenous catalyst (different state of matter)
  • N2 + H2 → 2NH3
• Contact process: V2O5
  
  • heterogenous
  • 2SO2 + O2 → 2SO3
• decomposition of hydrogen peroxide: MnO2
  
  • heterogenous
  • 2H2O2 → 2H2O + O2
• hydrogenation (organic): Ni / Pt / Pd
  
  • C2H4 + H2 → C2H6
• Fe2+ catalysts in oxygen transport → haemoglobin

Question 23

What are complex ions?

Answer 23

• transition metal cations + ligands

Question 24

What are ligands?

Answer 24

• species with non-bonding e- pair (neutral or anion)
• non-bonding pair → dative bonding with transition metal cation
• ex: H2O, NH3, Cl-, OH-
• strength determined by spectrochemical series

Question 25

What is coordination number?

Answer 25

• number of ligands in a complex ion (number of dative bonds)

Question 26

What are colours of some of the complex ions?

Answer 26

• [Cu(H2O)6]2+
  
  • blue
• [CuCl4]2-
  
  • yellow
• [Cu(NH3)4]2+
  
  • deep blue
• [Fe(H2O)6]2+
  
  • pale green
• [Fe(H2O)6]3+
  
  • pale violet
• [Mn(H2O)6]2+
  
  • pink

Question 27

Why are complex ions coloured?

Answer 27

• ligand electrodensity causes repulsion → d-orbital split
  
  • 2 energy levels
  • reduced splitting: pi overlap of lone pair with ligand
• VIS region radiation passes → e- excited to higher d-orbital
  
  • wavelength absorbed → complementary colour visible

Question 28

On what do colours depend?

Answer 28

• nature of ligand → weak and strong field
• transition metal cation
  
  • oxidation

Question 29

What are isoelectric complexes?

Answer 29

• same number of e-
  
  • Mn2+ and Fe2+ with water
• greater splitting for Fe2+ → higher nuclear charge
  
  • more repulsion

Question 30

What is ionic bonding?

Answer 30

• electrostatic attraction between positive and negative ions
• e- transferred from 1 ion to another