atomic structure

isotopes definition

atoms of the same elements with the same number of protons but different number of neutrons

cation

pos charged ion

anion

neg charged ions

relative atomic mass definition

avg weighted mass of an atom relative to one atom of carbon-12

why do isotopes have identical chemical properties

have exact same number of electrons and electron configuration - which determines how an atom reacts

why do isotopes have different physical properties

their differing masses lead to slight variation in physical properties such as = density, rate of diffusion and M and B points

factors affecting ionisation energies (IE)

• nuclear charge = more protons means more attraction of the electrons to the nucleus, so more energy is needed to remove elec. IE is greater

• distance from nucleus = electrostatic attraction is decreased, so less energy needed to remove an elec. IE is lower

• shielding = more electron means lower effective nuclear charge so lower IE

4 stages of TOF

• ionisation

• acceleration

• Ion drift

• detection

ionisation (electron impact)

• vaporised sample is injected at low pressure

• An electron gun fires high energy electrons at the sample

• This knocks out an outer electron

• Forms a positive ion with different charges

ionisation (electrospray)

• sample is dissolved in a volatile, polar solution

• Then injected through a fine needle giving a fine mist

• The tip of the needle has a high voltage

• At the tip the sample molecule gains a proton (H+ ion)

• Sample(X) becomes XH+

• The solvent evaporates away while the ions move towards the negative plate

acceleration of ions

• pos ins are attracted towards a neg plate

• and accelerated by the same kinetic energy

• so the speed is dependant on the mass of the molecule

ion drift

• ions enter a region with no electric field

• ions with diff masses = diff time of flight

• lighter ions/ higher charge = reach detector first

ion detection

• detector is a neg charged plate

• when ion hits it = current produced

• size of the current = no. of ions hitting the plate and therefore the abundance of the molecule

kinetic energy eq

• ke in J

• mass in kg

• v in ms…

velocity eq

v = d divided by t

(d = length in m)

(t = TOF in s)

relative atomic mass eq

isotopic mass x abundance

---

total abundance

subshells

s = 2

p = 6

d = 10

f = 14

orbitalls

each holds 2electrons

s = 1

p = 3

d = 5

f = 7

transition metals losing electrons

4s is lost before 3d

exceptions of electron configurations

chromium and copper

ionisation energy defiitions

the enthalpy change when one mole of gaseous atoms(/ions with a single/double/triple pos charge) is converted into one mole of gaseous ions with a single/double/triple pos charge

successive ionisation energies

the energy required too remove subsequent moles of electrons from gaseous ions

short electron configuration

go all the way right (noble gas)

and go 1 period above

use that noble gas as a shortcut

the number is the period the element is in

And the subshell is always S

ionisation energy trends = down a grp

• first ionisation energy decreases

• bcz outer electron is further away from nucleus = weaker electrostatic attraction, outweighing the increase in nuclear charge

ionisation energy trends = across a period

• 1st ionisation energy increases

• bcz nuclear charge increases and atomic radius decreases, so stronger attraction between outer electron and nucleus

• exceptions = Mg-Al and P-S

molecular ion peak

the peak with the highest m/z value

(biggest peak)

represents the mass/charge value of the molecule

evolution of atomic models

daltons solid sphere

thompsons plum pudding model

rutherfords nuclear model

bohrs planetary model with electron shells

modern quantum mechanical model

why is Mg-Al an exception for IE

• Al’s outer electron is inna 3p orbital

• Mg’s outer electron is in a 3s orbital

• 3p subshell is higher in energy than the 3s

• Al’s 3p electron is shielded by the 3s electrons

• so less energy is needed to remove it

why is P-S an exception for IE

• in S the outer electron is in a paired 3p orbital

• in P the electrons in the 3p orbitals are all unpaired

• in S theres a repulsion between the paired electrons

• so less energy is required to remove an electron from S than P

mass number of an isotope definition

Total number of protons and neutrons in the nucleus of an atom