3.1.1 Atomic Structure Flashcards
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
1/2000
What is the relative charge of a proton?
+1
What is the relative charge of a neutron?
0
What is the relative charge of an electron?
-1
Mass number [definition]:
The total number of protons and neutrons in the nucleus of an atom
Atomic number [definition]:
The number of protons in the nucleus of an atom
Ion [definition]:
A charged particle formed when one or more electrons are lost or gained by an atom or molecule
Ions [2]:
- Negative ions have more electrons than protons
- Positive ions have more protons than electrons
Isotope [definition]:
An atom with the same number of protons but a different number of neutrons
Calculating Ion Charge:
Ion Charge = number of protons - number of electrons
Overall charge [2]:
- The overall charge of any chemical substance will be zero.
- So cations will always be accompanied by anions in solid or in solution.
The relative atomic mass of an isotope (abundance):
. 100
John Dalton’s atomic model [4]:
- 19th century
- He described atoms as solid spheres
- He said that these solid spheres that made up different atoms
- He believed that atoms were a fundamental unit of matter and were indivisible
J.J Thompson’s model of the atom (plum pudding)
[3]:
- In 1897 he concluded that atoms must contain even smaller atoms (electrons)
- He discovered that atoms were divisible
- He viewed the atom as a large positively charged sphere with embedded, smaller, negatively charged electrons
When was the golden foil experiment conducted and by whom?
In 1909, Ernest Rutherford and his students Hans Geiger and Ernest Marsden conducted the gold foil experiment
The Gold foil experiment [2]:
- Ernest Rutherford and his students fired positively charged alpha particles at a very thin sheet of gold
- Rutherford believed that electrons were in a cloud around the nucleus of an atom
What did the gold foil experiment mean? [3]:
- Most of the alpha particles went through the gold which indicated that there is empty space in an atom
- A few particles were deflected suggesting that there is a positive mass in the centre of the atoms
- This disproved the plum pudding model as if it were true all the particles would’ve been deflected by the gold
What did Scientists realise about Rutherford’s cloud of electrons?
Electrons in a cloud around the nucleus would quickly spiral down into the nucleus and collapse
Bohr’s atomic model [4]:
- Electrons only exist in fixed orbits
- Each shell has a fixed energy
- When an electron moves between shells, electromagnetic radiation is emitted or absorbed
- Due to the energy of shells being fixed the radiation will have a fixed frequency
Modern atomic models [3]:
- Scientists later discovered that not all electrons in a shell had the same energy, which meant that Bohr’s model wasn’t quite right
- The most refined model we have today is based of quantum mechanics
- The quantum mechanics model explains some observations Bohr’s does not. Scientists tend to use whichever model is relevant to what they are investigating
Relative atomic mass [definition]:
The relative atomic mass is the average mass of an atom of an element
Relative isotopic mass [definition]:
The mass of an atom of an isotope of an element
Relative molecular mass [defintion]:
The relative molecular mass is the average mass of a molecule
Relative formula mass [definition]:
The average mass of a formula unit
What does a mass spectrometer show? [3]:
- Information about the relative atomic mass of an element
- The relative abundance of its isotopes
- The relative molecular mass of a molecule -
What are the four stages when a sample is put into a Time Of Flight(TOF) mass spectrometer?
- Ionisation
- Acceleration
- Ion drift/ deflection
- Detection
What are the two methods of ionising the sample in a mass spectrometer? [2]:
- Electrospray ionisation
- Electron impact ionisation
Electrospray ionisation [3]:
- sample dissolved in volatile solvent and pushed through a small nozzle at high temperature
- A high voltage is applied to it, causing it to gain a H⁺ ion
- The solvent is removed, leaving a gas made up of ions
Electron impact ionisation [3]:
- sample is vaporised
- electron gun is used to fire high energy electrons at sample
- This knocks one electron off each particle they become +1 ions
Acceleration [3]:
- The positive ions are attracted by an electric field
- This electric field gives the same amount of energy to each ion
- The lighter ions experience a greater acceleration, however, they are still given the same amount of energy as the heavy ions
Ion drift/deflection [3]:
- The ions enter a region with no electric field
- They drift through it at the same speed as when they left the electric field
- Lighter ions will be drifting at higher speeds
Detection [3]:
- lighter ions travel through the drifts at higher speeds, they reach the detector in less time than the heavier ones
- The detector detects the current created when the electrons hit it
- The spectrometer records how long it takes to pass through the spectrometer
What is the data collected from the mass spectrometer used for?
It is used to calculate the mass/charge values used to produce a mass spectrum
Mass spectrum [definition]:
A type of chart produced by a mass spectrometer
Identifying mass using a mass spectrum [2]:
- Elements with different isotopes produce than more than one line in a mass spectrum because the isotopes have different masses
- This produces characteristic patterns that can be used to identify certain elements
Electron Shells [3]:
- electrons have fixed energies in current model of atom
- Electrons move around the nucleus in certain regions of the atom called shells or energy levels
- The further a shell is from the nucleus the higher its energy and the larger its principal quantum number
What are the different types of subshells? [4]:
- s
- p
- d
- f
Orbitals [2]:
- The sub-shells have a different number of orbitals
- Each orbital can hold up to 2 electrons
What is a mass spectrometer used for?
to determine all the isotopes present in a sample of
an element and to therefore identify elements
What is electron impact used for? [2]:
- Elements and substances with low formula mass.
- Electron impact can cause larger organic
molecules to fragment
What is electrospray ionisation used for? [2]:
- Electrospray ionisation is used preferably for larger organic molecules.
- ‘softer’ conditions of this technique mean
fragmentation does not occur.
First ionisation energy [definition]:
The enthalpy change when 1 mole of gaseous atoms forms 1 mole of gaseous ions with a charge of 1+
Second ionisation energy [definition]:
The second ionisation energy is the enthalpy change when 1 mole of gaseous ions with a single positive charge forms 1 mole of gaseous ions with a 2+ charge
Factors that affect ionisation energy [3]:
- more protons in the nucleus the greater the attraction
- bigger the atom the further the outer electrons are from the nucleus and the weaker the attraction to the nucleus
- Shielding of the attraction of the nucleus- electrons in outer shell are repelled by electrons in complete inner shells, weakening the attraction of the nucleus
Why are successive ionisation energies always larger?
When the first electron is removed a positive ion is formed.
The ion increases the attraction on the remaining electrons and so the energy required to remove the next electron is large
K.E =
1/2 x m x v^2
Distance =
speed x time
what is kinetic energy measured in?
joules
what is mass measured in (TOF)?
Kg
What is velocity measured in (TOF)?
m s^-1
(TOF) no. of mol =
no. of particles
- ———————–
6. 02 x 10^23
What is Cl2 m/z peak ratio
9:6:1
