3.1 Physical Chemistry: .1 Atomic Structure Flashcards
(53 cards)
what did Robert Boyle propose? and state the time that this theory came to be.
- boyle proposed that there were some substances that could not be made simple. These were chemical elements as we know them.
- 1661
what did Greek philosophers believe when it came to the make up of everything on the earth?
-matter was made up of a single continuous substance that produced the four elemetns- earth, fire, water and air
what did John Dalton propose? and state the time that this theory came to be.
- dalton described atoms as solid spheres (indivisible)
- he also said that different spheres make up different elements
what did JJ Thompson propose? and state the time that this theory came to be.
-JJ discovered the electron. he showed that electrons were negatively charged (through his plum pudding model) and electrons from all elements were the same.
what did Henry Becquerel propose? and state the time that this theory came to be.
- henri discovered radioactivity which showed that particles could come from inside an atom
- 1896
what did Earnest Rutherford propose? and state the time that this theory came to be.
- Rutherford and his team conducted the famous gold foil experiment (they fired positively charged alpha particles at a very thin sheet of gold).
- plum pudding suggested that most alpha particle would be slightly deflected by the positive part of the atom but actually most passed through with a small number being delflected back.
- so rutherford developed the nuclear model of the atom which had a tiny positively charged nuclues surrounded by a cloud of negative electrons
what did Niels Bohr propose? and state the time that this theory came to be.
- scientists quickly realised that electrons in a cloud would quickly around the nucleus of an atom would quickly spiral down into the nucleus causing the atom to collaps
- bohr proposed a new model where the atoms exist in shells or orbits of fixed energy
how was Bohr’s model refined?
scientist later discovered that not all electrons in a shell have the same energy which meant Bohr’s model was not quite right so they refined it to include sub shells
on a periodic table what does the top number (the relative atomic mass tell you?
-the amount of protons and neutrons in a atom
on a periodic table what does the bottom number (the atomic number) tell you?
the number of protons (also electrons as the number of protons are equal to the number of protons)
what is the atom made up of?
proton, electrons and neutrons
for each particle state the mass and the charge: proton neutron and electron
proton: mass=1 charge= +1 electron: mass= 1/1840 charge= -1 neutron: mass=1 charge=0
what forces can be found in a atom?
-strong nuclear force: this force holds together the protons and neutrons in the centre of the atom -electrostatic force: this force holds protons and electrons together in the atom, it is less strong than the nuclear force
what is the equation for relative atomic mass
Ar= average mass of 1 atom/ (1/12) mass of 1 atom of carbon 12
what is the equation for the relative molecular mass
Mr= average mass of the molecule/ (1/2) mass of 1 atom of carbon 12
what are isotopes?
isotopes have the same atomic number but different mass numbers they have the same number of protons and same number of electrons but different number of neutrons
why are isotopes chemically identical?
they are chemically identical because they have the same number of electrons
why do isotopes have different physical properties?
they have different physical properties because they have different masses e.g Cl (35) has a higher mass, higher density higher melting and boiling point slower rate of diffusion
what is does mass spectrometry help you to determine?
the relative atomic mass
what are the stages inv mass spectrometry?
vaporisation, ionisation, acceleration, separation and detection
what happens in the normal type of mass spectrometry?
-the sample is injected in and vaporised in a gaseous atom -the sample is ionised by high energy electrons shot from the electron gun. ionisation must occur for the next stages M(g) —> Mg+ + e- -a pair of parallel plates plates generate and electric field which forms a column for fast moving electrons. The first plate is positive with respect to the second plate -in the separation stage ions are separated depending on the mass to charge ratio (m/z). Ions with a smaller mass to charge ratio are deflected more easily and hit the detector however increasing the magnetic field allows ions with a greater m/z values to hit the detector. -in the detection stage when ions hit the detector, a current is produced which causes a pen deflection and a peak is drawn on the spectrum
what happens in a TOF mass spectrometer
-the whole apparatus is kept under a high vacuum to prevent the ions that are produced colliding with molecules from the air -the is sample dissolved in a volatile solvent which is passed through an inlet valve, this is connected to the positive terminal of aa high voltage supply. the sample is ionised at a voltage of 3-4kV producing positively charged droplets. The solvent evaporates from the droplets, the droplets get smaller and smaller until they are a single positively charged ion. M(g) —> Mg+ + e- -the ions are attracted by a negatively charged plate, they gain kinetic as they are accelerating towards the negatively charged plate. As Ke= 1/2mv^2 those particles with a higher mass to charge ratio will move with a lower velocity (smaller ions move with a higher speed, larger ions move with a lower speed) -in the drift region is a high vacuum region. The electrons pass through forming a beam and travel along a tube, called the flight tube to the detector. The ions enter the drift region with different speeds hence they will be separated in the drift region as smaller ions will have a shorter time of flight and reach the detector first -the flight times of the ions are recorded and the positive ions pick up an electron from the detector which causes a current to flow.
how has the TOF spectrometer been improved?
the vaporisation, ionisation and acceleration has been combined -as the sample dissolved in solvent leaves the end of the capillary, the sample is ionised as a voltage of 3-4kV is applied to the end of the capillary -the droplet leaving the capillary is full of ions, the solvent evaporates and a spray of gaseous ions is produced -ions are attracted by the extraction electrode. all the ions gain the same kinetic energy and enter the drift region -the drift region is a high vacuum region where no electric fields are present.
how is a current generated in the mass spectrometer?
the ion hits the detector and gains an eleton which allows a current to flow
the current is amplified and the peak is created
