Atomic strucuture Flashcards
What is the mass number?
The number of protons and neutrons
What is the atomic number?
The number of electrons and protons
How do isotopes differ to atoms?
They are of the same element but with a different mass number
they have the same chemical properties but different physical properties
- lower density
- faster rates of diffusion
- lower melting and boiling points
What is relative isotopic abundance?
The percentage of each isotope in a sample that is present in nature
What is the mass spectrometer ?
An instrument to accurately determine the relative isotopic mass and the relative abundance of isotopes
also separates atoms or molecules according to there charge and mass
What are the 4 stages in a mass spectrometer?
Ionisation - where the atoms are converted into a +1 ion
Acceleration- where the ions move at the same speed
Flight tube - time taken for them to travel a fixed distance
Detection- when they arrive at a detector
Describe the two ways ionisation occurs ?
Electron gun ionisation- the sample is gaseous and hit with high energy electrons from an electron gun which knocks off the outer shell electron
Electro spray ionisation - add a proton in the form of H+, once the sample has dissolved in a solvent of H+ ions
It is pushed through a needle with high voltage and the protons will stick
Describe acceleration
The positively charged ions are attracted by the negatively charged plate. The ions of the same charge will move at the same speed so they will have the same kinetic energy
Describe the flight tube
The ions will pass through into a tube the time of flight of each particle. The time taken depends on the velocity which depends on the mass of the ion
Ion detector
The ion detector is a negatively charged
As the ion hits the detector they produce an electric current
A high current means a high abundance of the specific ion
The mass spectrometer converts the size of the current into a peak on a mass spectrum
One of the methods of ionising samples for TOF mass spectrometry is by electron impact. How is this ionisation done?
High energy electrons are fired from an electron gun at the sample
which knocks off one electron
A method of ionising samples is by electrospray ionisation. How is this done?
Dissolve sample in a volatile solvent
injected through a fine needle at high voltage
to gain a proton
explain why different ions take different tmes to travel through the flight tube
Due to the velocity of the
What is the difference between the rutherford model and the current atomic model?
The atomic model has protons and neutrons
The current model shown electrons in different energy levels/orbitals
Define relative atomic mass
The average mass of an isotope of an element compared to 1/12th of the mass of carbon 12
Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer
Ions not molecules will interact with and be accelerated by an electric field
Only ions will create a current when hitting the detector.
state the role of water in the reaction with calcium
To be an oxidizing reagent
State and explain the trend in the first ionization energies of the elements in the group 2 from magnesium and to barium
A decreasing trend
As Ions get bigger they have a weaker attraction to lost ion
state the element in period 3 that has the highest first ionization energy
Argon- Largest proton so has largest nuclear charge but has the same amount of shielding as the other period 3s
Explain why the second ionization energy of boron is higher then the first ionisation energy
As the electron is now being taken away from a positive ion
how do TOF mass spectrometers separate two species to give two peaks
Positive ions are accelerated by an electric field
to a constant kinetic energy
the lighter ion will travel faster and so more of them will reach the detector first
define ionisation energy?
The energy required to remove 1 mole of electrons from one mole of gaseous products
How are ions detected in TOF?
the ions gain an electron at the ion detector and create a current
How is abundance measured?
the abundance is proportional to the size of the current
