atomic structure Flashcards
what do atoms consist of?
● central, small nucleus
● protons and neutrons in nucleus
● surrounded by electrons in energy levels
how are the electrons arranged?
2 . 8 . 8 . 2
what is the relative mass of a proton?
1
what is the relative charge of a proton?
1+
what is the relative mass of a neutron?
1
what is the relative charge of a neutron?
0
what is the relative mass of an electron?
1/2000
what is the relative charge of an electron?
1-
what is the atomic number?
● number of protons in nucleus
● way to remember: atomic so at the bottom because it’s so small
what is the mass number?
● number of protons + number of neutrons
● way to remember: MASSive so at the top
what do atoms of the same element all have the same number of?
● protons
● protons determines what type of atom it is
what are isotopes?
● atoms of the same element with same number of protons and different number of neutrons
●same atomic number but different mass number
what did john dalton describe atoms as?
● solid spheres
● spheres made up different elements
what did j.j thomson discover and what model did he propose?
● electron
● new model made ‘plum pudding model’
● positively charged pudding, electrons inside
what experiment did rutherford conduct?
gold foil experiment
what was the gold foil experiment?
● fired positive alpha particles at thin gold sheet
● most particles passed through but some deflected
● so must be positive nucleus
what was the nuclear model?
● tiny positively charged nucleus surrounded by a ‘cloud’ of negative electrons
● most of atom is empty space
why was nuclear model wrong?
cloud around nucleus of atom would spiral into nucleus causing atom to collapse
what was the model niels bohr proposed?
electrons are in shells
how was the bohr model refined?
included sub-shells
why is the bohr model still used today?
simple and explains many experimental observations
what do all types of TOF mass spectrometry rely on?
● forming ions from samples
● separating ions depending on their m/z (mass charge) ratio
what are the types of ionisation in TOF mass spectrometry?
● electron impact (aka electron bombardment)
● electron spray ionisation
what is electron impact ionisation?
● sample analysed is vaporised
● high energy electrons fired at it (from electron gun)
● knocks off 1 electron from each particle forming a 1+ ion
● fragmentation occurs
● for smaller molecules
what is the symbol equation for electron impact ionisation?
● X(g) -> X⁺(g) + e⁻
● include state symbols
what does volatile mean?
easily evaporates
what is electron spray ionisation?
● sample dissolved in volatile solvent (water)
● injected through fine hypodermic needle to give fine mist (aerosol)
● tip of needle attached to positive terminal of high voltage power supply
● particles ionised by gaining proton (ie H⁺ which is 1 proton) from solvent as they leave needle
● producing XH⁺ ions (ions with single positive charge and mass of Mr + 1)
● solvent evaporates away while XH⁺ ions are attracted towards a negative plate where they are accelerated
what is the symbol equation for electron spray ionisation?
● X(g) + H⁺ -> XH⁺ (g)
what is the technique of electron spray ionisation used for?
● substances with higher molecular mass
● including biological molecules like protein
what is the technique of electron spray ionisation known as?
soft ionisation as fragmentation rarely takes place
explain acceleration in TOF mass spectrometry
positive ions accelerated using electric field so they all have same KE
what is the equation for kinetic energy?
KE + 1/2mv^2
KE - (J)
m - (kg)
v - (m/s)
what is the equation for velocity?
v = √ 2KE / m
what does the velocity of each particle depend on?
● mass
● lighter particles have faster velocity
● heavier particles have slower velocity
explain ion drift in the flight tube in TOF mass spectrometry
● positive ions travel through hole in negatively charged plate into tube
● time of flight of each particle through flight tube depends on velocity which depends on mass
what is the equation for time of flight?
t = d / v
t = d x √m /2KE
t = (s)
d = (m)
v = (m/s)
explain detection in TOF mass spectrometry
● positive ions hit a negatively charged electric plate
● when they hit detector plate, positive ions are discharged
● by gaining electrons from the plate
● this generates a movement of electrons and an electric current that is measured
● size of current measured is proportional to the abundance
what are the rules of putting electrons into atomic orbitals?
● spin - 2 electrons in same orbital must have opposite spin
● aufbau principle - atomic orbitals with lower energy filled first
● hund’s rule - atomic orbitals of same energy fill singly before starting pair (of opposite spin)
how do you do electron configuration short structure?
put noble gas before: [Ne] 3s1
what are rules for electron configuration of transition metals?
● electron lost from 4s level first (fills first, empties first)
● as soon as electron enters the 4s orbital, energy increases to be greater than 3d
what are main levels and sub levels?
● main levels - 1, 2, 3 etc
● main levels have sub levels - s, p, d, f
how many orbitals do each sub level have?
● s has 1 orbital (holds 2 electrons)
● p has 3 orbitals (holds 6 electrons)
● d has 5 orbitals (holds 10 electrons)
● f has 7 orbitals (holds 14 electrons
what is the order of electron arrangement?
1s 2s 2p 3s 3p 4s 3d 4p
what is the electron configuration for copper?
● 1s2 2s2 2p6 3s2 3p6 4s1 3d10
● more stable configuration
what is the electron configuration for chromium?
● 1s2 2s2 2p6 3s2 3p6 4s1 3d5
● more stable configuration
what is ionisation energy?
● energy required to remove one mole of electrons from one mole of atoms in the gaseous state (kjmol-1)
● state symbols are essential when writing equation
what is the first ionisation energy?
● energy required to remove 1 electron from each atom in a mole of gaseous atoms producing one mole of unipositive gaseous ions
● Na(g) -> Na+ (g)+ e-
what is the second ionisation energy?
● energy required to move the second electron (not both)
● Na+(g) -> Na2+(g) + e-
what is the trend in ionisation energy down a group?
● generally decreases
● increased nuclear charge (more protons)
● atoms get bigger
● more shielding
● therefore, weaker attraction from nucleus to electron in outer shell
what is the trend in ionisation energy across a period?
● generally increases
● increased nuclear charge (more protons)
● atoms get smaller
● shielding stays the same
● therefore, stronger attraction from nucleus to electron in outer shell
what is the exception in the trend across a period?
● Mg -> Al
● electron lost from Al is lost from the p orbital, while that lost from Mg is from the s orbital
● P orbital has higher energy than S orbital, so easier to lose electrons
● N -> O
● in O, electrons are paired in the 2p orbital
● therefore, the repulsion between electrons make it easier to remove one of them
● P -> S
● in S, electrons are paired in 3p orbital
● therefore the repulsion between electrons makes it easier to remove one of them
why does atomic radius decrease across a period?
increase in nuclear charge attracts electrons more strongly, pulling them to nucleus
