Atomic Structure Flashcards
What is Mass number (A) (1)
⇒ Σ(proton+neutron)
What is an Isotope? (2)
⇒ Atoms of the same element that have the same number of protons (same atomic number) (1)
⇒ But a different number of neutrons (different mass number) (1)
Define Relative Molecular Mass (Mr). (2)
⇒ Mean mass of a molecule/(1/12th) mass of an atom of 12C (2)
Define Relative Atomic Mass (Ar). (2)
⇒ (Mean mass of 1 atom)/(1/12th) mass of 1 atom of 12C (2)
What is the use of mass spectrometry? (3)
⇒ Identify elements (1)
⇒ determining the relative molecular mass (Mr) of compounds (1)
⇒ gives information about the relative isotopic mass and relative abundance of isotopes. (1)
Why is it important that the instrument is in a vacuum? (1)
⇒ To prevent collision of ions with gas molecules. (1)
How are samples of gases, liquids, and solids inserted into the instrument? (3)
⇒ Gases and liquids must be volatile, and then inserted directly (2)
⇒ Solids must be vapourised into their gaseous form. (1)
What does Electron impact/gun involve? (3)
⇒ A vaporised sample is injected at a low pressure (1)
⇒ An electron gun fires high energy electrons at a sample (1)
⇒ Which knocks off an electron from the atom thus creating a positive ion (1)
Describe how molecules are ionised using electrospray ionisation. (3)
⇒ Sample is dissolved in a volatile solvent (1)
⇒ Injected through needle at high voltage (1)
⇒ Each molecule/particle gains a proton/H+ (1)
How would you work out the mass of an isotope/element, given the Avogadro’s constant? (1)
⇒ MASS = Mass No1 / Avogadro’s constant
e.g: ⁷⁹Br⁺
Mass = 79/6.022 x 10²³ = 1.31 x 10⁻²² grams
Kg = 1.31 x 10⁻²²/1000 = 1.31 x 10⁻²⁵ kg
What is the first step of mass spectrometry? (2)
⇒ IONISATION (1)
⇒ The sample loses an electron via electrospray or by High-speed electrons via electron gun. (1)
What is the second step In mass spectrometry, name and explain the process (3)
⇒ Acceleration (1)
⇒ Positive ions are accelerated by an electric field (1)
⇒ Giving all the ions the same kinetic energy (1)
What is the third step of mass spectrometry; name and explain the process (2)
⇒ Deflection (1)
⇒ a magnetic field will separate ions according to its M/Z ratio (1)
What is the fourth step of mass spectrometry; name and explain the process (3)
⇒ Detection (1)
⇒ ions will collect at a detector and generator a current (1)
⇒ the current ∝ abundance of the isotope (1)
Fifth extra step in mass spectrometry; state and explain the process. (2)
⇒ Data analysis (1)
⇒ The M/Z value and % abundance will be calculated and peaks will be displayed (1)
Explain how ions are detected and relative abundance is measured in a TOF mass spectrometer. (2)
⇒ ion hits the detector (1)
⇒ (relative) abundance is proportional to (the size of) the current (1)
How do we calculate the RAM from a graph? (1)
Σ(Μ/Ζ x relative abundance)/ Σ(relative abundance) (1)
A time of flight (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. (1)
⇒ 138Ba (1)
Why is the process of ionisation important? (3)
⇒ to allow the ions to be accelerated via electric field (1)
⇒ to allow the ions to be deflected via the magnetic field (1)
⇒ for the ion to produce and current and be detected at the detector (1)
State the difference, if any, in the chemical properties of isotopes of the same element. Explain answer (2)
⇒ No difference (1)
⇒ same electronic arrangement
Explain why it would be difficult to distinguish between 48Ti(2+) and 24Mg(+). (2)
⇒ Both ions have the same M/Z value of 24 (1)
⇒ deflected equally (1)
Define ionisation energy. (2)
⇒ is the energy required to remove 1 electron (1)
⇒ from a gaseous atom (1)
What is ionisation energy measured in? (1)
⇒ Kj mol^-1 (1)
What are the three factors that affect the ionisation energy of an element? (3)
⇒ Nuclear charge (1)
⇒ Distance from the nucleus (1)
⇒ shielding (1)
