3.1.1 - atomic structure

relative charges of protons, neutrons and electrons

• proton = +1

• neutron = 0 (neutral)

• electron = -1

relative masses of protons, neutrons and electrons

• proton = 1

• neutron = 1

• electron = 1/1840 or effectively 0

what are isotopes

atoms with the same number of protons, but different numbers of neutrons

• why do isotopes have similar chemical properties

• why do they have slightly varying physical properties

• they have the same electron configuration

• they have different masses

can an ion be an isotope

Yes, an atom can be an isotope and an ion simultaneously. For instance, a specific isotope of chlorine, like Chlorine-37, can lose or gain electrons to form an ion, such as the chloride ion (Cl⁻).

what does a time of flight (TOF) mass spectrometer measure (2)

• how heavy the different ions formed by a sample are (this is called m/z, where m = A_r of the ion and z = charge on the ion)

• how much of a particular ion there is (i.e. relative abundance)

because it measures mass of isotopes and abundance of isotopes, this can be used to find the r________ a_______ m____ and therefore identify the e________.

because it measures mass of isotopes and abundance of isotopes, this can be used to find the relative atomic mass (A_r) and therefore identify the element.

in substances made of molecules, a mass spectrometer can help us find the r_________ m____________ m____.

relative molecular mass

what happens in TOFMS (3)

• particles of the substance are ionised to form 1+ ions

• these = accelerated so they all have the same E_k

• time taken to travel a fixed distance = used to find mass of each ion in the sample 

name the 5 steps in a TOFMS

1. ionisation

2. acceleration

3. ion drift

4. ion detection

5. data analysis

diagram of the TOF mass spectrometer

STAGE 1: IONISATION

• what are the 2 ways the sample can be ionised

1. electron impact

2. electrospray ionisation

STAGE 1: IONISATION

in electron impact, sample being ionised is v__________. then, high energy e-s are f______ at it. this usually knocks off o___ e________ from each particle, forming a ___ ion.

 

in electron impact, sample being ionised is vaporised. then, high energy e-s are fired at it. this usually knocks off 1 electron from each particle, forming a 1+ ion.

STAGE 1: IONISATION

general eq. w/ state symbols to show ionisation of an atom

X _(g) —→ X⁺_(g) + e^-

STAGE 1: IONISATION

what fires the high energy electrons

an electron gun (a hot wire filament w/ a current running through it that emits electrons)

STAGE 1: IONISATION

where are the 1+ ions then attracted towards

• a negative electric plate

• where they are accelerated

STAGE 1: IONISATION

what elements and substances is electron impact used for

ones with a low M_r

electron impact is also used when the substance is an ELEMENT, not a molecule

STAGE 1: IONISATION

• when molecules are ionised with electron impact, what is the 1+ ion formed known as

• give an example equation for this, w/ state symbols, for methane

• a molecular ion

• CH₄(g) → CH₄⁺(g) + e⁻

STAGE 1: IONISATION

what happens in electronspray ionisation

(this is a perf mark scheme answer)

sample dissolved into a volatile solvent

then injected through a fine hypodermic needle at high voltage

(this gives a fine mist (aerosol))

sample gains a proton / H+

(next few flashcards are adding info to this, but this is pretty much all you need)

STAGE 1: IONISATION

what is the tip of the needle attached to

the + terminal of a high-voltage power supply

STAGE 1: IONISATION

how are the particles ionised

• by gaining a proton (e.g. a H⁺ ion which is just 1 proton) from the solvent as they leave the needle

• this produces XH⁺ ions (ions w/ a single positive charge and a mass of M_r + 1)

STAGE 1: IONISATION

general equation for electronspray ionisation w/ state symbols

X_(g) +  H⁺  —→ XH⁺ _(g)

STAGE 1: IONISATION

what happens to the solvent as the XH⁺ ions are attracted towards a negative plate (where they are accelerated)

it evaporates away

STAGE 1: IONISATION

• what substances is electrospray ionisation used for

• why is this

• ones with a high relative formula mass (including many biological molecules, e.g. proteins)

• so the molecules do not fragment

STAGE 2: ACCELERATION

• the positive ions are accelerated using a…

• why?

• electric field (there is an attraction between the + charged ions and the - charged plates)

• so that they all have the same E_k

STAGE 2: ACCELERATION

you’ll need to use the kinetic energy equation. give this and the units used.

(you need to know how to rearrange this too!)

E_k = 1/2mv²

E_k in J, mass in kg, velocity in m s^-1

STAGE 2: ACCELERATION

given that all the particles have the same E_k, the velocity of each particle depends on its…

mass

STAGE 2: ACCELERATION

l________ particles have a f________ v_________, and h_________ p___________ have a s________ v__________.

lighter particles have a faster velocity, and heavier particles have a slower velocity. (think about the equation)

STAGE 3: FLIGHT TUBE

the positive ions travel through a h____ in the n__________ c________ p______ into a t_____.

the positive ions travel through a hole in the negatively charged plate into a tube.

STAGE 3: FLIGHT TUBE

what does the TOF of each particle through this flight tube depend on

• velocity of particle

• (which in turn depends on its mass)

STAGE 3: FLIGHT TUBE

to find time of flight, we need what 2 equations?

kinetic energy eq (E_k = 1/2mv²) and distance speed time eq (d = v x t, where d = metres, v = m s^-1, and time = seconds)

STAGE 3: FLIGHT TUBE

lighter ions t______ f________ and reach detector in l____ t_____ than the h_________ p__________ that m_____ s_________ and t____ l__________ to reach detector.

lighter ions travel faster and reach detector in less time than the heavier particles that move slower and take longer to reach detector.

STAGE 4: DETECTION

• what happens when the positive ions hit the detector plate

• what does this generate

 

• they are discharged (by gaining electrons from plate)

• a movement of electrons, and hence an electric current that is measured

STAGE 4: DETECTION

what does the size of the current give a measure of

no. of ions hitting the plate (and therefore abundance)

STAGE 5: DATA ANALYSIS

a computer uses the data to produce a…

mass spectrum

what 2 things does this show

1. mass to charge (m/z) ratio

2. abundance of each ion that reaches the detector

since all ions produced by electrospray ionisation and most ions produced by electron impact = have a 1+ charge, what does this mean the m/z effectively is?

the mass of each ion (y / 1 = y)

formula for relative atomic mass (A_r)

A_r = (mass no. of iso. 1 x relative abundance of iso. 1) + (mass no. of iso. 2 x relative abundance of iso. 2) / combined abundance of all isotopes (might be 100, might not be!)

(the values in the A_r formula can be found on the mass spectrum. remember, don’t divide the percentages by 100!)

how to do a TOF calculation for 2 isotope ions traveling down the same flight tube (look in notes for examples)

the ions will be accelerated to the same kinetic energy. so E_k for one ion = E_k for another ion. then set up up eqs. with the substituted values to be equal to each other (1/2 mv² = ½ mv²). cancel out common terms on both sides (you don’t need to find masses on both sides separately). then rearrange and solve

• energy levels are divided into…

• sub-levels consist of a set number of…

• orbitals are a region of space that can hold up to…

• you can’t say w____ an e- is in an orbital and where it’s going n___

• sub-levels

• orbitals

• 2 e-

• you can’t say where an e- is in an orbital and where it’s going next

• how many sub-levels are there?

• give the names of these

• 3

• s, p and d

how many orbitals does each sub-level hold

• s = 1

• p = 3

• d = 5

therefore, how many e- are in each sub-level

• s = 2

• p = 6

• d = 10

give the order of sub-levels for e- configs.

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s…

here is a diagram of e- configs. in boxes.

• in this, what is an e-?

• what is an orbital?

• what is a sub-level?

• what is an energy-level?

• one of the arrows in a box (called a single-headed arrow, they look more like the data sign than in this diagram)

• a box

• a row

• a group of sub-levels (e.g. the rows 2s and 2p make up the 2nd energy level)

in the e- config., what do you write next to each of the sub-levels?

how many e- are in that sub-level (amnt. of orbitals x2)

REMEMBER: when filling up the boxes, put one arrow in each box FIRST and then go back and fill them so they each have 2.

how do you write simplified versions of e- configs.?

find the total number of e- in your config., then find a noble gas with the highest possible atomic number that could fit into that. then write the noble gas symbol in square brackets, and if there are any sub-levels left, write those afterwards too.

• for this diagram, give the e- config

• then give the simplified e- config

• then name what element this is

• 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

• [Ar] 4s¹

• potassium (K) because atomic number (Z) = 19

• elements in the periodic table are in different…

• what are these blocks called?

• where is each block on the periodic table?

• blocks

• s, p, d or f block

• (see photo)

in the s-block (according to their e- configs.), what do atoms have in common in terms of their outermost e-?

the outermost e- are in an s sub-level

in the p-block (according to their e- configs.), what do atoms have in common in terms of their outermost e-?

the outermost e- are in a p sub-level

in the d-block (according to their e- configs.), what do atoms have in common in terms of their outermost e-?

the final e- enters a d-orbital (research this)

how would you change the e- config. of an atom to be the e- config. of an ion?

add or subtract e- (as an ion is an atom that has lost or gained e-)

there’s a catch for d-block elements, though. with d-block elements, it’s the ___ electrons which are lost f____.

with d-block elements, it’s the 4s electrons which are lost first (even though the 4s orbital is filled before the 3d orbital during electron configuration).

e.g. e- config. for Fe atom (Z = 26) → [Ar] 4s² 3d⁶

then e- config. for Fe²⁺ ion = [Ar] 3d⁶

COVER IONISATION ENERGIES

what 3 factors affect IEs

• distance between the nucleus and the e- being removed

• shielding (repulsion) by e-s in inner shells between nucleus and outer e-s

• nuclear charge

1st ionisation energy def

energy required to remove one mole of e-s from one mole of gaseous atoms

if first IE is low

electron is lost more easily

1st, 2nd, 3rd IE

Na (g) —→ Na+ (g) + e- (this ion is formed after the 1st IE has been measured)

Na+ (g) —→ Na2+ (g) + e-

Na2+ (g) —→ Na3+ (g) + e-

explaining significant jumps in ionisation energies (ENERGY LEVELS AND THEIR DISTANCE FROM THE NUCLEUS)

• (number of, e.g. 1st) e- is removed from the (number of, e.g. 3rd) energy level / (name of, e.g. 3s) sub-level

• which is further / closer to the nucleus

• more / less shielded by inner shells of e-s

• and therefore more / less tightly held

• than the (number of, e.g. 2nd) e-

• which is removed from the (number of, e.g. 2nd) energy level / (name of, e.g. 2p) sub-level

general trend in 1st IEs going across period 3 (INCREASING NUCLEAR CHARGE, BUT SAME SHIELDING)

as atomic no. increases —→ first IE of period 3 elements also increases

• bc nuclear charge increases

• outer e- has a stronger force of attraction to the nucleus

• more and more energy is required to remove it

• even though there is little change between distance between outer e- and nucleus and amount of shielding between them

what are always (?) the anomalies in this trend

group 2-3 and group 5-6 (3 and 6 are lower)

why is this (SUB LEVELS AND DISTANCE)

• outer e- in Al is lost from the 3p sub level

• this is further away from the nucleus

• less shielded by inner shells of e-s

• so the outer e- is less attracted to the nucleus than the outer e- of Mg 

• which is removed from the 3s sub-level

why is the 1st IE of S (grp 6) lower than P (grp 5) (ORBITALS)

• in S, 2e-s are in 3p orbital

• these repel each other

• takes less energy to remove one of the electrons from this pair than it does to remove the 1st e- of P

• where all the 3p orbitals are singly occupied