Physical: Atomic Structure Flashcards
What is the relative mass of an electron?
1/1840
Why are there no units for relative mass/charge?
It’s because the values are relative to one another, it’s a COMPARISON and the actual values are too small
How should you draw electrons in diagrams?
by using crosses
X
How are electrons arranged?
in energy LEVELS (not shells)
What is the atomic number and its symbol?
the number of protons in the nucleus.
number of protons defines the element
Z
What is mass number and its symbol?
TOTAL number of protons and neutrons in the nucleus
A
What is an ion?
a charged particle formed when an atom gains or loses and electron
What is an isotope?
atoms of the same element that have the same number of protons and have a different number of neutrons
What are the three main physical properties?
boiling point
melting point
density
Do isotopes have similar chemical properties?
yes, because isotopes have the same number of electrons in outer shell
AND have the same electron configuration
Do isotopes have similar physical properties?
No, they have different physical properties because isotopes have different mass numbers (due to diff. number of neutrons).
What is the difference between relative atomic mass and mass number?
rel. atomic mass= MEAN mass of an atom on a scale where an atom of C-12 is exactly 12 (taking isotopes into account) *** can be a decimal number
mass number= number of protons and neutrons ** has to be a full number
What instrument can be used to find the relative proportions of an element?
mass spectrometer
What are the 4 stages (+1 extra) of mass spectrometry?
- ionisation (by either electron impact or electrospray ionisation)
- acceleration
- ion drift
- detection
- data analysis
What is the process of electron impact?
method of ionising elements
- sample is vaporised
- high energy particles are fired from an ELECTRON GUN
- they bombard a sample
- knock one OUTER electron off forming a 1+ ion
What type of ions can electron impact work with?
usually, low Mᵣ ions
What is the formula for electron impact?
X₍g₎——> X⁺₍g₎ + e⁻
What is the con of electron impact?
it can cause fragmentation (breaking the ion)
What is the process of electrospray ionisation?
- sample is dissolved in a volatile solution
- it is injected through a fine hypodermic needle, producing a fine mist
- tip of the needle has a high voltage
- each particle gains a H⁺ (proton) to form a 1+ ion
What type of ions does electrospray ionisation work with?
high Mᵣ ions
this is because they are more likely to fragment so cannot use electron impact method
What is the formula for electrospray ionisation?
X₍g₎ + H⁺ ——–> XH⁺ ₍g₎
always include state symbols
What is the process of acceleration (mass spectrometry)?
- the +ions are accelerated in an ELECTRIC FIELD by a force of attraction by a negatively charged plate
- until they all have CONSTANT kinetic energy (not speed)
Does mass affect velocity of ions in mass spectrometry?
yes,
- heavier ions are slower
- lighter ions are faster
What is ion drift?
- ions enter a FLIGHT TUBE directed towards a director
- length of time to reach the detector depends on the mass/velocity
Does a heavier ion a shorter/longer flight time?
a heavier ion has a longer flight time
a lighter ion has a shorter flight time
What is the formula for time of flight along flight tube?
t= d* √m/2KE
substitute distance/time into velocity of kinetic energy formula
What is detection (mass spectrometry)?
- the + ions hit a negatively charged plate
- ions gain electrons
- movement of e⁻ generates an electric current
- size of current is proportional to the number of ions gaining e⁻
What is the name of the graph produced from mass spectrometry?
mass spectra
What does the number of peaks on a mass spectra indicate?
the number of peaks = number of isotopes
most abundant one has the highest peak
What is the definition of ionisation energy?
the energy change when one mole of electrons are removed from one mole of GASEOUS atoms to form 1 mole of gaseous positively charged ions
What is the formula for first ionisation ?
X(g) ————> X⁺₍₉₎ + e⁻
Can non-metals be ionised?
all elements can be ionised, even the ones that normally form 1- ions (non-metals)
What state must the elements be in to become ionised?
always must be in a GASEOUS state
What are the factors affecting ionisation energy?
- shielding
- nuclear strength
- distance from the nucleus
How does nuclear charge/strength affect ionisation energy?
- more protons there are in the nucleus, stronger the nuclear attraction for valence e⁻
- more energy needed to remove the e⁻, greater I.E
How does distance form the nucleus affect ionisation energy?
- further from the nucleus the valence electron is, the weaker the nuclear attraction
- less energy required to remove e⁻
- lower I.E
How does shielding affect ionisation energy?
- greater the number of inner e⁻ between the nucleus and the valence e⁻
- weaker the nuclear attraction (between nucleus and valence e⁻)
- less energy required to remove valence e⁻
- lower I.E
What ion would have the greatest ion drift?
the lightest ion
What is the trend for the first ionisation energies down Group 2?
as you go down the group, the IE₁ decreases
- each element has one more electron shell than the one above it
- the extra shell, means more shielding e⁻ and an increasing distance from the nucleus which reduces the nuclear attraction
- so less energy required to remove the outer e⁻
What are the ionisation trends across Period 3?
across a period, IE tend to increase because:
- this is because the number of protons increase as you go across a period (so nuclear strength increases)
- however, all extra electrons are at the same shells so not much change in shielding and distance
- so more energy required to remove the outer e⁻
What is the shape of the graph for ionisation energies across Period 3?
up down up up down up up
What is the trend for successive ionisation energies of elements?
-general increase
Explain why there is a huge jump on graphs for successive ionisation energies of elements
there are big jumps when a new energy shell is broken into, so outer e⁻ are closer to nucleus and fewer shielding e⁻ os nuclear attraction increases, more energy required to remove outer e⁻
Explain why there is a gradual increase on graphs for successive ionisation energies of elements?
within each shell, successive ionisation energies increase gradually because e⁻ are being removed from an increasingly positive ion, so there is less repulsion amongst the remaining e⁻, so they’re held more strongly by the nucleus, so less of a big jump
During mass spectrometry, why could the relative atomic mass be different from its actual value?
this could be due to other isotopes present
Why could there be a small peak on a mass spectra that is half the actual relative atomic mass?
it could be because a two + ion is formed from the isotope that it is half of
e.g- if a peak is at 64 for Te 128 (not Te 126 which is another isotope)
Would the atomic radius of ¹²⁴Te be larger than ¹³⁰Te?
it would be the same because they both have the same number of electrons and has the same electron configuration
Why is it necessary to ionise molecules during TOF mass spectrometry?
- ions can be accelerated by an electric field
- so that it can be deflected by a magnetic field
- so that it can be detected by a detector
What is the formula used to find the mass of an ion/atom?
m= Aᵣ/1000 * L
L=avogadro’s constant
L=6.022 x 10²³
What is the formula used to find the time of flight if you are given the mass of two ions (for mass spectroscopy)?
m₁/t₁²=m₂/t₂²
What is the formula to find the mass of an atom/ion (mass spectrometry)?
2Eₖ * t²/d²=m
Why must atoms be ionised to T.O.F mass spectrometry?
atoms must be ionised because:
- only ions can be accelerated in an electric field
- only ions can create a current in the detector
- so they can be deflected/to bend beam
Why is there a vacuum in the flight tube?
to ensure that ions travel at a constant speed (do not decelerate by colliding with air)
How do you determine the number of atoms of a specific mass in a mass spectrometer?
by looking at the size of the current
What is the definition of relative atomic mass?
it is the average mass of one atom compared to the mass of an atom of one C-12
Why do particles with the same mass and velocity can be deflected by different amounts in the same magnetic field?
this could be because they have a different charge
What does the amount that an ion is deflected depend on?
the lighter the ion, the more deflected it is
the higher the charge of the ion, the more deflected it is
What is an orbital?
a region of space where an electron is likely to be found 90% of the time
What are subshells?
shells are divided into subshells,
electrons in different subshells have different energies
What are the four types of subshells?
s
p
d
f
How many orbitals does an s subshell have?
1 orbital
maximum 2 electrons
How many electrons can each orbital carry?
2 electrons per orbital
How many orbitals does a p subshell have?
3 orbitals
max. 6 electrons
How many orbitals does a d subshell have?
5 orbitals
max. 10 electrons
How many orbitals does an f subshell have?
7 orbitals
max. 14 electrons
What subshells exist in the first shell?
1s subshell
2 electrons in shell
What subshells exist in the second shell?
2s, 2p
8 electrons in shell
What subshells exist in the third shell?
3s, 3p, 3d
18 electrons in shell
What subshells exist in the fourth shell?
4s, 4p, 4d, 4f
32 electrons in shell
What are two exceptions to the orbital rule?
chromium and copper
they donate one of their electrons from the 4s subshell to the 3d subshell because they prefer a more stable full/half full subshell
What is the rule for electrons filling in the 3rd and 4th shell?
have to fill in 4s subshell before filling up 3d subshell
What is the electron configuration of Cr?
1s²2s²2p⁶3s²3p⁶3d⁵4s¹
not 3d⁴4s² as you might expect
Using orbitals, explain why there is a drop IE between Mg and Al between group 2 and 3?
in aluminium, outer e⁻ is removed from the 3p subshell, which has a higher energy than the 3s subshell so it is further from the nucleus (as it has more energy) so reduced nuclear attraction
less energy required to remove outer electron
Using orbitals, explain why there is a drop in ionisation energy between P and S?
in sulfur, there is one paired group of e⁻ in the 3p subshell, which causes repulsion between the paired e⁻ so less energy is required to remove electron from shared orbital
Draw the mass spectrum for ³⁵Cl (75%) and ³⁷Cl (25%)?
peaks at 72, 74, 70
70 highest
72 2nd highest
74 lowest
Why has Na a much lower first ionisation energy than neon?
This is because Na will have its outer electron in a 3s shell further from the nucleus and is more shielded. So Na’s outer electron is easier to remove and has a lower ionisation energy.
Why does He have the highest first ionisation energy?
because its outer e⁻ are in the first shell closest to the nucleus so there is no shielding and the distance is less. Has a bigger IE than H because it has 2 protons (not one) so stronger nuclear force
If chlorine exists as two isotopes, and hydrogen and carbon exist as one isotope
each, how many molecular ion peaks will be shown in the mass spectrum of C4H6Cl4?
5
With this electron configuration: [Ar] 4s²3d³
how many outer electrons does this element have?
5
because 3d has more energy than 4s slightly so at a similar distance from the nucleus
How can observations from reactions show that an element can exist in two oxidation states?
because 2 difference colours of solution will be displayed because each colour is due to each oxidation state
Is the second ionisation energy larger than the first ionisation energy
yes, because the electron is being removed from a positive ion (not an atom) so the nuclear attraction is stronger, so more energy required
also the electron being removed is closer to the nucleus
What can be adjusted in the mass spec. to enable ions formed by the different isotopes to be directed onto the detector?
electromagnet/electric field, magnet
What is deflection (mass spectroscopy)?
when ions are deflected by a magnetic field
depends on the mass and charge of the ion on how much it has been deflected, same m/z ratio, same deflection
What is the evidence for the max. no. of e⁻ that can be held in an s sub-level on the graph for IE across periods?
there are 2 elements before the drop in energy
What evidence from the graph supports says that no more than three unpaired
electrons can be accommodated in the 3p sub-level?
drop in IE between P and S
What is the relative isotopic abundance?
it is the proportion of each type of isotope present in the sample of the element naturally
How do you calculate relative atomic mass from absolute mass?
absolute mass of one thing x 6.022x10²³
