CHEMISTRY 101: ATOMS & MOLECULE
Chemistry QUIZES AND ANSWERS ON
CHLORINE
A student studying GCSE science is puzzled by data which indicate that a sodium atom is larger
than a chlorine atom and that a sodium ion is smaller than a chloride ion. How should an A-level
Chemistry student explain this apparently conflicting information. (6) A chlorine atom has
more protons in it's nucleus compared to a sodium atom
Both have 3 shells of electrons
Electrons more strongly attracted by chlorine nucleus
so size smaller than Na
An electron shell is lost when a sodium atom turns into a sodium ion
Inner electrons more strongly attracted so ion smaller than atom
An electron is added to the outer shell when a chloride ion is formed
Greater repulsion between shells so size of chloride ion bigger than chlorine atom
What is the relative mass of an electron?(1) 1/1840
Explain why isotopes have similar chemical properties(2) Identical electron configuration
Chemical properties depend on electrons
Define the term relative atomic mass.(1) (average mass of an atom/ 1/12 mass of 1 atom of
carbon 12
Explain, in detail, how the relative atomic mass of this element can be calculated from data
obtained from the mass spectrum of 3 different isotopes(5) Mass spectrum gives m/z
value
Mass spectrum gives relative abundance
Multiply m/z by relative abundance for each isotope
Sum these values
Divide by the sum of relative abundances
,Use your knowledge of structure and bonding to explain why the melting point of iodine is low
(113.5 °C) and why that of hydrogen iodide is very low (-50.8 °C).(6) I2 is molecular
HI is molecular
IM forces hold the molecules together
There are weak IM forces in both molecules hence why melting points are low
I2 bigger molecule so has more electrons
Therefore stronger van der Waals between molecules in I2 that need more energy to break
causing the melting point to be higher.
HI also shows permanent dipole-dipole attraction between molecules but these forces are less
than the vdW forces in iodine.
Chloroethane reacts with potassium hydroxide in the presence of propan-1-ol to form ethene.
State the role of potassium hydroxide and the role of propan-1-ol in the reaction.(2) KOH =
base
propan-1-ol = solvent
Write an ionic equation, with state symbols, to show the reaction of calcium with an excess of
water.(1) Ca(s) + 2H20(l) > Ca2+(aq) + 2OH-(aq) + H2
Outline how the TOF mass spectrometer is able to separate two species to give two peaks.(4)
Positive ions accelerated by electric field
To a constant kinetic energy
The lighter ions have the same kinetic energy and move faster
Therefore the lighter ions arrive first
State and explain the general trend in first ionisation energy across Period 3.(4) General
increase
Increasing nuclear charge
Similar shielding
Stronger attraction from the nucleus for outer electrons.
State the element in Period 3 that has the highest melting point.
Explain your answer.(4) Silicon
, Giant covalent structure
Many covalent bonds
Need a lot of energy to overcome
Explain why nickel is ductile (can be stretched into wires).(1) Layers can slide over
eachother
In a mass spectrometer, the relative abundance of each isotope is proportional to the current
generated by that isotope at the detector. Explain how this current is generated.(3)
Electrons transferred at the detector
From the detector to the + ion
Current produced related to abundance
Aluminium chloride has a relative molecular mass of 267 in the gas phase. Deduce the formula
of the aluminium compound that has a relative molecular mass of 267(1) Al2Cl6
AlBr3
Explain why the ionisation energy of every element is endothermic.(1) Energy needed to
overcome the attraction between positive nucleus and negative electrons
Sometimes the mass spectrum of Kr has a very small peak with an m/z value of 42. Explain the
occurrence of this peak.(2) The isotope (84)Kr
Has two electron knocked off/gets a 2+ charge
State the trend in first ionisation energies in Group 2 from beryllium to barium. Explain your
answer in terms of a suitable model of atomic structure.(3) Decreases
Atomic radius increases
As group descends more shielding
Explain why the second ionisation energy of sodium is greater than the second ionisation
energy of magnesium.(3) Na2+ requires loss of electron from 2p subshell AND Mg2+
requires loss of electron from 3s subshell
Less shielding in Na
So more attraction of electron to the nucleus
Explain why sodium has a lower melting point than magnesium.(3)Na has smaller nuclear
charge
Chemistry QUIZES AND ANSWERS ON
CHLORINE
A student studying GCSE science is puzzled by data which indicate that a sodium atom is larger
than a chlorine atom and that a sodium ion is smaller than a chloride ion. How should an A-level
Chemistry student explain this apparently conflicting information. (6) A chlorine atom has
more protons in it's nucleus compared to a sodium atom
Both have 3 shells of electrons
Electrons more strongly attracted by chlorine nucleus
so size smaller than Na
An electron shell is lost when a sodium atom turns into a sodium ion
Inner electrons more strongly attracted so ion smaller than atom
An electron is added to the outer shell when a chloride ion is formed
Greater repulsion between shells so size of chloride ion bigger than chlorine atom
What is the relative mass of an electron?(1) 1/1840
Explain why isotopes have similar chemical properties(2) Identical electron configuration
Chemical properties depend on electrons
Define the term relative atomic mass.(1) (average mass of an atom/ 1/12 mass of 1 atom of
carbon 12
Explain, in detail, how the relative atomic mass of this element can be calculated from data
obtained from the mass spectrum of 3 different isotopes(5) Mass spectrum gives m/z
value
Mass spectrum gives relative abundance
Multiply m/z by relative abundance for each isotope
Sum these values
Divide by the sum of relative abundances
,Use your knowledge of structure and bonding to explain why the melting point of iodine is low
(113.5 °C) and why that of hydrogen iodide is very low (-50.8 °C).(6) I2 is molecular
HI is molecular
IM forces hold the molecules together
There are weak IM forces in both molecules hence why melting points are low
I2 bigger molecule so has more electrons
Therefore stronger van der Waals between molecules in I2 that need more energy to break
causing the melting point to be higher.
HI also shows permanent dipole-dipole attraction between molecules but these forces are less
than the vdW forces in iodine.
Chloroethane reacts with potassium hydroxide in the presence of propan-1-ol to form ethene.
State the role of potassium hydroxide and the role of propan-1-ol in the reaction.(2) KOH =
base
propan-1-ol = solvent
Write an ionic equation, with state symbols, to show the reaction of calcium with an excess of
water.(1) Ca(s) + 2H20(l) > Ca2+(aq) + 2OH-(aq) + H2
Outline how the TOF mass spectrometer is able to separate two species to give two peaks.(4)
Positive ions accelerated by electric field
To a constant kinetic energy
The lighter ions have the same kinetic energy and move faster
Therefore the lighter ions arrive first
State and explain the general trend in first ionisation energy across Period 3.(4) General
increase
Increasing nuclear charge
Similar shielding
Stronger attraction from the nucleus for outer electrons.
State the element in Period 3 that has the highest melting point.
Explain your answer.(4) Silicon
, Giant covalent structure
Many covalent bonds
Need a lot of energy to overcome
Explain why nickel is ductile (can be stretched into wires).(1) Layers can slide over
eachother
In a mass spectrometer, the relative abundance of each isotope is proportional to the current
generated by that isotope at the detector. Explain how this current is generated.(3)
Electrons transferred at the detector
From the detector to the + ion
Current produced related to abundance
Aluminium chloride has a relative molecular mass of 267 in the gas phase. Deduce the formula
of the aluminium compound that has a relative molecular mass of 267(1) Al2Cl6
AlBr3
Explain why the ionisation energy of every element is endothermic.(1) Energy needed to
overcome the attraction between positive nucleus and negative electrons
Sometimes the mass spectrum of Kr has a very small peak with an m/z value of 42. Explain the
occurrence of this peak.(2) The isotope (84)Kr
Has two electron knocked off/gets a 2+ charge
State the trend in first ionisation energies in Group 2 from beryllium to barium. Explain your
answer in terms of a suitable model of atomic structure.(3) Decreases
Atomic radius increases
As group descends more shielding
Explain why the second ionisation energy of sodium is greater than the second ionisation
energy of magnesium.(3) Na2+ requires loss of electron from 2p subshell AND Mg2+
requires loss of electron from 3s subshell
Less shielding in Na
So more attraction of electron to the nucleus
Explain why sodium has a lower melting point than magnesium.(3)Na has smaller nuclear
charge
