3.1.1 Atomic Structure PPQs Flashcards
Explain how gaseous atoms of Rubidium are ionised using electron impact ionisation in a mass spectrometer. [2 marks]
- high energy electrons fired at sample from an electron gun
- high energy electrons knock off one electron from each atom, forming a positive ion
Write an equation, including state symbols, to show the process that occurs when the first ionisation energy of rubidium is measured using electron impact ionization. [1 marks]
Rb(g) → Rb+(g) + e–
State one reason why the first ionisation energy of rubidium is lower than the first ionisation energy of sodium. [1 mark]
- Rb is a bigger atom so electron further from nucleus
- electron lost from a higher energy level
- more shells so More shielding in Rb so less attraction of nucleus in Rb for outer electron
By reference to the relevant part of the mass spectrometer, explain how the
abundance of an isotope in a sample of rubidium is determined. [2 makrs]
Relevant part: Detector
Explanation: Current / electrical signal produced proportional to abundance
Predict whether an atom of 88Sr will have an atomic radius that is larger than, smaller than or the same as the atomic radius of 87Rb. Explain your answer. [3 marks]
- Smaller
- Bigger nuclear charge / more protons in Sr
- Same shielding
Predict the element in Period 3 that has the highest 2nd IE [2 markks]
Na - electron removed from the 2p orbital
Explain why the IE of every element is endothermic [1 mark]
energy needed to overcome the attraction between the negative electron and positive nucleus
define the term relative atomic mass [2 marks]
average mass of one atom of an element / 1/12 mass of one atom of 12C
which isotope is deflected most by magnetic field of a mass spectrometer?
the one with lowest m/z
complete the electronic configuration of tellurium: [Kr]
[Kr] 5s2 4d10 5p4
suggest what might cause the relative atomic mass of an element from a mass spec to be different to the one on the periodic table
- other isotopes present/some isotopes absent
- different abundances of isotopes
predict whether the atomic radius of 124Te is larger than, smaller than, or the same as, the atomic radius of 130Te [2 marks]
the same
same no. protons AND same electron configuration
Identify the period 3 element that has the highest melting point. Explain your answer. [4 marks]
- silicon
- macromolecular structure
- covalent bonds between atoms
- many strong covalent bonds need lots of energy to break
which transition metals have exactly 3 unpaired electrons in their ground state?
Vanadium and Cobalt
Name the two methods of ionisation in a mass spectrometer
electrospray and electron impact ionisation
which transition metal has only 1 unpaired d electron as an atom?
Scandium
An atom has 2 more protons and 3 more neutrons than an atom of 52Cr.
Deduce the symbol, including the mass number and the atomic number, for this atom.
57 26 Fe
State two differences between the ‘plum pudding’ model and the model of atomic structure used today.
- central nucleus contains protons and neutrons
- Electrons are now arranged in energy levels/shells/orbitals
Magnesium exists as three isotopes: 24Mg, 25Mg and 26Mg. In terms of sub-atomic particles, state the difference between the three isotopes of magnesium. State how, if at all, the chemical properties of these isotopes differ and give a reason for your answer. [3 marks]
- 24Mg has 12n; 25Mg has 13n; 26Mg has 14n OR They have different numbers of neutrons
- No difference in chemical properties Because all have the same electronic structure (configuration)
Table 1 shows some data about fundamental particles in an atom. An atom of hydrogen can be represented as 1H. Use data from Table 1 to calculate the mass of this hydrogen atom.
1.6734 × 10^−24 g
Which one of the following is a fundamental particle that would not be deflected by an electric field?
A electron
B neutron
C proton
B neutron
Deduce the number of protons in 182W
74
Deduce the number of neutrons in 186W
112
Define the term atomic number.
Number of protons in the nucleus
Explain why atoms of an element may have different mass numbers.
They may have different numbers of neutrons
When He2+ particles were fired at a thin sheet of gold, most of the particles were detected at point P. What conclusion can be drawn from the detection of He2+ particles at point P?
Gold atoms are mainly empty space.
When He2+ particles were fired at a thin sheet of gold, about 1 in 8000 of the particles were detected at point Q. What conclusion can be drawn from the detection of He2+ particles at point Q?
Gold atoms have a small, positive nucleus
Define the term relative atomic mass.
average mass of an atom or isotopes divided by the mass of 1 atom of 12C, multiplied by 12
Explain, in detail, how the relative atomic mass of an element can be calculated from data obtained from the mass spectrum of the element.
- Spectrum gives (relative) abundance and m/z
- Multiply m/z by relative abundance for each isotope
- Sum these values
- Divide by the sum of the relative abundances
Define the term mass number of an atom.
Mass number = number of protons + neutrons
write an equation to represent the second ionisation of strontium
Sr+(g) -> Sr2+ + e-
define the term ‘first ionisation energy’
the amount of energy required to remove one mole of electrons from one mole of atoms in the gaseous state
write an equation for the second ionisation energy of oxygen
O+(g) -> O2+(g) + e-
On 2 axes, add crosses to estimate the successive ionisation energies of oxygen.
Explain why the second ionisation energy of boron is higher than the first ionisation energy of boron.
Outer electron is being removed from a positive ion and therefore requires more energy
Identify the diagram in the figure below that shows the correct relative sizes of the ions in sodium fluoride. Justify your answer.
B: Both Na+ and F– same electron arrangement (isoelectronic). Na+ has more protons so stronger attractions for outer electrons
Explain why the second ionisation energy of calcium is lower than the second ionisation energy of potassium. [2 marks]
- In Ca+ outer electron is further from nucleus
- More shielding in Ca+
Identify the s-block metal that has the highest first ionisation energy.
Be
Deduce which of Na+ and Mg2+ is the smaller ion. Explain your answer.
Mg2+ because Mg2+ has more protons and has the same shielding
State and explain the general trend in the values of the first ionisation energies of the elements Na to Ar. [3 marks]
- Trend : Increases (1)
- Increased nuclear charge or proton number AND the shielding remains the same (1)
- Stronger attraction between nucleus and outer e– (1)
Explain why the value of the first ionisation energy of magnesium is higher than that of sodium.
- Increased nuclear charge
- Same shielding
Explain why the value of the first ionisation energy of neon is higher than that of sodium.
- Electron removed from a shell of lower energy
- Less shielding
Predict whether an atom of 88Sr will have an atomic radius that is larger than, smaller than or the same as the atomic radius of 87Rb. Explain your answer. [3 marks]
- Smaller
- Bigger nuclear charge / more protons in Sr
- Similar/same shielding
The Ne atom and the Mg2+ ion have the same number of electrons. Give two reasons why the first ionisation energy of neon is lower than the third ionisation energy of magnesium.
- Mg2+ ion smaller than Ne atom so Mg2+ e– closer to nucleus
- Mg2+ has more protons than Ne / e– is removed from a charged Mg2+ion vs neutral Ne atom
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 marks]
- A Cl atom has more protons in its nucleus than a Na atom has
- Both have 3 shells of electrons
- Electrons more strongly attracted by Cl nucleus so size smaller than Na
- An electron shell is lost when a Na ion is formed from a Na atom
- Inner electrons more strongly attracted so ion smaller than atom
- An electron is added to the outer shell when a Cl ion is formed
- Greater repulsion between shells so size of chloride ion greater than Cl atom
Element Q forms a sulfate with formula QSO4. Which of these could represent the electronic configuration of an atom of Q?
B
Tellurium is the element with atomic number of 52. Complete the electron configuration of tellurium.
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p4
Explain why the first ionisation energy of sulfur is different from that of phosphorus.
- e− paired in 3p orbital in S
- Paired e− repel so less energy needed to remove
Draw a cross on the diagram to show the first ionisation energy of aluminium.
Al between 500 – 700 (between Na and Mg)
State which of the first, second or third ionisations of aluminium would produce an ion with the electron configuration 1s2 2s2 2p6 3s1
Second
State the trend in first ionisation energies in Group 2 from beryllium to barium.
- Decreases
- Atomic radius increases
- As group is descended there is more shielding
- Less attraction between the nucleus and the outer electron
What is the maximum number of electrons that can be accommodated in an s sub-level?
2
What evidence from the diagram supports the fact that 2 electrons max can be in an s sub-level?
Two elements before the drop in energy to Al
What evidence from the diagram supports the fact that the 3p sub-level is higher in energy than the 3s?
ionisation energy of Al < that for Mg
What evidence from the diagram supports the fact that no more than three unpaired electrons can be accommodated in the 3p sub-level?
- fall in energy from P to S
- From Al to P there are 3 additional electrons
Describe how the molecules are ionised using electrospray ionisation. [3 MARKS]
- Sample is dissolved in a volatile solvent
- Injected through hypodermic needle at high voltage
- Each molecule/particle gains a proton/H+
Explain how ions are detected and relative abundance is measured in a TOF mass spectrometer. [2 marks]
- ion hits the detector and gains an electron
- relative abundance is proportional to the size of the current
Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer [2 marks]
- Ions, not molecules, will interact with and be accelerated by an electric field
- Only ions will create a current when hitting the detector
A sample of ethanedioic acid was treated with an excess of an unknown alcohol in the presence of a strong acid catalyst. The products of the reaction were separated and analysed in a time of flight (TOF) mass spectrometer. Two peaks were observed at m / z = 104 and 118. Outline how the TOF mass spectrometer is able to separate these two species to give two peaks. [4 marks]
- Positive ions are accelerated by an electric field to a constant kinetic energy
- The positive ions with m / z of 104 have the same kinetic energy as those with m / z of 118 and move faster
- Therefore, ions with m / z of 104 arrive at the detector first
Calculate the mass, in kg, of one atom of 46Ti
A molecule Q is ionised by electron impact in a TOF mass spectrometer. The Q+ ion has a kinetic energy of 2.09 x 10^–15 J. This ion takes 1.23 x 10^–5s to reach the detector. The length of the flight tube is 1.50 m Calculate the relative molecular mass of Q.
169
A naturally occurring sample of the element boron has a relative atomic mass of 10.8. In this sample, boron exists as two isotopes, 10B and 11B. Calculate the percentage abundance of 10B in this naturally occurring sample of boron.
20%
A sample of strontium has a relative atomic mass of 87.7 and consists of three isotopes, 86Sr, 87Sr and 88Sr. In this sample, the ratio of abundances of the isotopes 86Sr :87Sr is 1:1. Calculate the percentage abundance of the 88Sr isotope in this sample.
80%
A TOF mass spectrum was obtained for a sample of barium that contains the isotopes 136Ba, 137Ba and 138Ba. The sample of barium was ionised by electron impact. Identify the ion with the longest time of flight.
138Ba+
A sample contains two isotopes of Copper, 63B and 65B. 63B has an abundance 2.33 times greater than 65Cu. Calculate the relative atomic mass of the sample to one decimal place.
63.6
In a time of flight mass spectrometer, molecule X is ionised using electrospray ionisation. What is the equation for this ionisation?
X(g) + H+ → XH+(g)
Define the term relative molecular mass (Mr).
average mass of one molecule / 1/12th atom of C12
Which shows the electron configuration of an atom of a transition metal?
A [Ar] 4s2 3d0
B [Ar] 4s2 3d8
C [Ar] 4s2 3d10
D [Ar] 4s2 3d10 4p1
B - Nickel
A sample of the element Q consists of several isotopes. All of the Q+ ions in the sample of Q that has been ionised in a TOF mass spectrometer have the same kinetic energy. The time of flight of a 82Q+ion is 1.243 × 10−5 s. Calculate the time of flight of the 86Q+ion.
The mass spectrum of tellurium also has a small peak at m/z = 64 despite the Ar being 128. Explain the existence of this peak.
2+ ion formed / 2 electrons removed From 128 (Te)
