Atomic structure Flashcards
What happens during Flight Mass spectrometer?
[Vacuum]
The whole apparatus is kept under a high vacuum to prevent the ions that are produced colliding with molecules from the air
[Ionisation]
> (electrospray ionisation) the sample is dissolved in a volatile solvent and forced through a fine hollow needl that is connected to the positive terminal of a high voltage supply. This produces tiny positively charged droplets that have gained a proton from the solvent
> The solvent evaporates from the droplets into the vacuum and the droplets get smaller and smaller until they may contain no more than a single positively charged ion
> (Electron impact) the sample is vaporised and high energy electrons are fired at it from an electron gun. which is a hot wire filament with a current running through it that emits beam of high energy electrons
This usually knocks off one electron from each particle forming a l+ ion
[Acceleration]
> The positive ions are attracted towards a negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve a higher speed
[Ion Drift]
> The ions pass through a hole in the negatively charged plate. forming a beam and travel along a tube, called the flight tube, to a detector
[Detection]
When ions with the same charge arrive at the detector, the lighter ones are first as they have higher velocities. The flight times are recorded. The positive ions pick up an electron from the detector, which causes a current to flow. When ions with the same charge arrive at the detector, the lighter ones are first as they have higher velocities. The flight times are recorded. The positive ions pick up an electron from the detector, which causes a current to flow.
[Data Analysis]
The signal from the detector is passed to a computer which generates a mass spectrum
What is time of flight spectrometer used for?
they are used by forensic scientists co help identify substances such as illegal drugs
Space probes carry mass spectrometers. They are used to identify the elements in rock samples
Used to identify the different isotopes that make up an element
What is high resolution mass spectrometry?
Is when a mass spectrometer can measure relative atomic masses to five decimal places of an atomic mass unit
How has the atom developed overtime?
1661: Robert Boyle proposed that there were some substances that could not be made simpler
1803: John Dalton suggested that elements were composed of indivisible atoms. All the atoms of a particular element had the same mass and atoms of different elements had different masses. Atoms could not be broken down
1896: Henri Becquerel discovered radioactivity. This showed that particles could come from inside the atom. Therefore the atom was not indivisible
J J Thomson discovered the electron. Electrons were negatively charged and electrons from all elements were the same. Electrons were located within the atom in circular arrays like plums in a pudding of positive charge.
1911: Ernest Rutherford and his team found that most of the mass and all the positive charge of the atom was in a tiny central nucleus
1913: Niels Bohr put forward the idea that the atom consisted of a tiny positive nucleus orbited by negatively-charged electrons to form an atom like a tiny solar system. The electrons orbited in shells of fixed size and the movement of electrons from one shell to the next explained how atoms absorbed and gave out light. This marking the beginning of quantum theory.
1926: Erwin Schrodinger worked out an equation that used the idea that electrons had some of the properties of waves as well as those of particles. This led to a theory called quantum mechanics which could be used to predict the behaviour of subatomic particles
1932: Chadwick discovered the neutron
How is the atom put together?
The protons and neutrons are in the centre of the atom, held together by a force called the strong nuclear force - hold electrons and protons together in the atom, so it overcomes the repulsion between the protons in the nucleus
The nucleus is surrounded by electrons. Electrons are found in a series of levels, sometimes referred to as orbits or shells, which gel further and further away from the nucleus
What was Gilbert Lewis theory?
the inertness of the noble gases was related to their having full outer shells of electrons
atoms could also bond by sharing electrons to form full outer shells
ions were formed by atoms losing or gaining electrons to attain full outer shells
What evidence did Thompson use to come up with the theory of the plum pudding model?
> As he believed that there was something that accounted for the rest of the mass of the atom - as electron were too small
> Because electrons were negative, he believed there was some source of positive charge
What is the Mass (kg), Charge (C) of a proton?
Mass (kg) : 1.673 x 10-27
Charge (C) : +1.602 x 10-19
What is the Mass (kg), Charge (C) of a Neutron?
Mass (kg) : 1.675 x 10-27
Charge (C) : 0
What is the Mass (kg), Charge (C) of Electron?
Mass (kg) : 0.911x10 -30
Charge (C) : -1.602 x 10-19
How are electrons found when are the nucleus?
Electrons are found in a series of levels - known as orbitals/shells
What is relative atomic mass (Ar)?
Is the average mass of atom of an element on a scale where an atom of carbon-12 is 12
What is relative isotopic mass?
Is the mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is 12
What is the relative atomic mass (Ar)?
1/12 mass of 1 atom of 12C
What is the Relative Molecular Mass (Mr)?
1/12 mass of 1 atom of 12C
