1.1 Atomic Structure Flashcards
relative charge of a proton
+1
relative charge of a neutron
0
relative charge of an electron
-1
relative mass of a proton
1
relative mass of a neutron
1
relative mass of an electron
1/1836
what is the atomic number? (Z)
number of protons
what is the mass number (A)
total number of protons and neutrons
how to calculate number of neutrons
mass number - atomic number
what holds an atom together
the electrostatic attraction between the positive nucleus and the negatively charged electrons
what are isotopes?
atoms of the same element that contain the same number of protons and electrons but different number of neutrons
why do isotopes of the same element display the same chemical characteristics?
they have the same number of electrons in their outer shells
what is the physical difference of isotopes?
the number of neutrons and therefore the mass
what is relative atomic mass
average mass of an isotope compared to C-12
How to calculate the relative atomic mass (Ar)
(relative abundance of isotope 1 x mass of isotope 1) + (relative abundance of isotope 2 x mass of isotope 2) etc / 100
what is mass spectrometry used for?
- accurate determination of the Ar of an element, based on the abundance and mass of its isotopes
4 key stages of time of flight mass spectrometry
- ionisation
- acceleration
- ion drift
- detection
what are the two key methods of ionisation in mass spectrometry
electron impact
electrospray ionisation
which ionisation method is used for substances with lower molecular mass?
electron impact
how is a sample ionised in electron impact ionisation
the sample is vaporised and bombarded with high energy electrons fired from an electron gun
what does the electron gun do
it emits electrons as a current runs through a hot wire filament
what is the result of the bombardment of electrons
an electron is knocked off each particle, forming a 1+ ion.
X (g) → X+ (g) + e-
what are the ions formed in electron impact ionisation called?
molecular ions / M+ ions
what happens to the molecular ions after they are formed?
they are attracted to a negatively charged plate and accelerated through the mass spectrometer
what occurs after the molecular ion is formed
the molecular ion can fragment into smaller ions, which are also detected
which ionisation method is typically used for substances with higher molecular mass?
electrospray ionisation
what is a characteristic of electrospray ionisation that differs from electron impact?
fragmentation is unlikely to happen - it is considered a soft ionisation technique
how is the sample prepared for electrospray ionisation
the sample is dissolved in a volatile solvent and injected into the mass spectrometer
what happens when the sample is injected in electrospray ionisation
How are they ionised + what does it produce
it produces a fine mist or aerosol, and the particles are ionised by gaining a proton from the solvent
what happens to the XH+ ions after they are formed in electrospray ionisation?
the solvent evaporates and the XH+ ions are attracted to a negatively charged plate, accelerating them through the mass spectrometer.
what happens once the sample is ionised
the 1+ ions are accelerated using an electric field.
what is a key principle regarding the kinetic energy of 1+ ions?
all 1+ ions are accelerated to have the same kinetic energy.
how does the mass affect the velocity of 1+ ions?
lighter ions move faster, whilst heavier ions move slower.
what happens to the 1+ ions after they are accelerated?
they pass through a hole in the negatively charged plate and move into a flight tube
what does the time of flight of each 1+ ion depend on?
their velocity
what happens to the 1+ ions after they pass through the mass spectrometer?
they hit a negatively charged “detector” plate
what occurs when the 1+ ions hit the detector plate?
they gain an electron, discharged the ion and producing a current
what is the relationship between the current produced and the abundance of ions?
the size of the current is proportional to the abundance of those ions hitting the plate
how is the data from the detector processed?
the detector plate is connected to a computer which produces the mass spectrum
formula for velocity
(d/t)
formula for Ek
Ek = 1/2 x m x v^2
what are the first 4 subshells
s, p, d, f
what is elements have an f shell?
elements with more than 57 electrons
sodium has 11 electrons, what is the electronic configeration
1s2, 2s2, 2p6, 3s1
what are valence electrons?
the electrons located in the outermost electron shell
what is ionisation energy?
energy required to remove on electron from each atom in 1 mole of gaseous atoms - to form 1 mole of gaseous ions.
what are the units of IE
kJ mol -1
what is the FIRST ionisation energy
energy required to remove one electron from one mole of atoms to form one mole of 1+ ions
what does the charge of an ion equate to?
the level of ionisation energy
eg Cl 4+ = fourth level of ionisation
what is the size of the first IE affected by?
- nuclear charge
- distance from valence electrons to the nucleus
- shielding
what happens to the first ionisation energy across a period?
FIRST IONISATION ENERGY INCREASES ACROSS A PERIOD
what happens to the first ionisation energy down a group-
FIRST IONISATION ENERGY DECREASES DOWN A GROUP
why does ionisation energy increase across a period?
- nuclear charge increases
- therefore, atomic radius of atoms decreases
- shielding remains quite constant
- harder to remove an electron so more energy is needed
why are there slight decreases in IE1 between beryllium and boron
because the 5th electron of boron is in the 2p subshell - which is further away from the nucleus than the 2s subshell of beryllium
why is there a slight decrease in IE1 between nitrogen and oxygen
due to spin-pair repulsion in the 2Px orbital of oxygen.
in oxygen there are 2 electrons in the 2px orbital, so repulsion between those electrons makes it easier for one of those electrons to be removed
why is there a decrease in ionisation energy from one period to the next
- there is increased distance between nucleus and valence electrons
- increased shielding
why does ionisation energy decrease down a group
- number of protons is increased, so nuclear charge increased.
- distance between nucleus and outer electron increases
- shielding increases
