Atomic Structure

describe the atom

• nucleus made up of protons and neutrons

• electrons orbiting in shells, take up most space in the atom

what makes up most of an atoms mass

nucleus

relative charge of all subatomic particles

proton, +1

neutron, 0

electron, -1

relative mass of all subatomic particles

proton, 1

neutron, 1

electron, 1/1840

mass number definition

total number of protons and neutrons

atomic/proton number definition

number of protons

why are all atoms neutral

number of protons = number of electrons

ion definition

atoms which have lost or gained electrons = charged atom

what does proton number determine

the element

what do electrons determine

reactivity properties

what determines physical properties

number of protons, neutrons and its electron configuration (determines bonding)

define isotope

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

what do different isotopes have

differ in physical properties due to different number of neutrons

first hypothesis for atoms

atoms are spheres,

different elements are made from different spheres,

indivisible

who made the first hypothesis for atoms

greeks

J.J. Thompson theory for atoms

• discovered the electron

• atom wasn't solid and was made of other particles

• positive atom with electrons embedded

ernest rutherford nuclear model

• discovered the nucleus, found it was very small and positive

• found atom was empty space

• positive nucleus with negative electrons orbiting

gold leaf experiment and findings

positive alpha particles fired at thin gold leaf

• most went through, showing mostly empty space

• some deflected, showing small positive nucleus

what problem did niels bohr find with rutherford model

the cloud of electrons could collapse into the positive nucleus

what did niels bohr find

fixed energy levels: shells

what did James Chadwick find

neutrons

describe nuclear model

positive nucleus with protons and neutrons

electrons orbit in fixed energy levels

existence of sub shells

Erwin Schrödinger theory

orbitals

steps of time of flight mass spectrometry

1. vaporisation

2. ionisation

3. acceleration

4. ion drift

5. detection

two types of ionisation

electrospray

electron impact

describe electron impact

vaporised sample,

high energy electrons fired by an electron gun to form a positive ion,

electrons knocked off,

fragmentation occurs

describe electrospray ionisation

sample dissolved in a high, volatile solvent,

sample injected into a fine hypodermic needle and an aerosol is created,

high voltage is passed through causing loss of electron

acceleration

positive ions are passed through an electric field, particles with a lower m/z ratio will accelerate quicker

ion drift

particles travel through with a constant speed and kinetic energy

particles with lower m/z travel faster

detection

ions hit negative detector plate and produce a current as they gain an electron

how is abundance measured in tof mass spec

abundance is directly proportional to size of current

electron impact equation

X(g)→ X+ (g) + e-

electrospray ionisation equation

Xg) + H+ (g) -> XH+(g)

relative atomic mass

average mass of an atom of an element, relative to 1/12th of an atom of carbon 12

relative molecular mass

average mass of a molecule, relative to the mass of 1/12th of carbon 12

relative isotopic mas

mass of an atom of a particular isotope compared to one-twelfth of the mass of a carbon-12 atom

relative atomic mass equation

draw a mass spectra produced by tof

what does a mass spectra show

abundance of different isotopes present

how are molecules different in mass spec

fragments are created, molecular ion peak is equal to the relative atomic mass

what is the molecular ion peak

last significant peak on a mass spectra, equal to relative atomic mass peak at 100

4 sub shells

s,p,d,f

how many electrons in an s sub shell

2

how many electrons in a p sub shell

6, 3 pairs

how many electrons in a d sub shell

5 pairs, 10 electrons

how do electrons fill in orbitals

separately first, then they pair up

electron configuration for chromium

1s2 2s2 2p6 3s2 3p6 3d5 4s1

one 4s moves to 3d so it is half full and more stable

electron configuration for copper

1s2 2s2 2p6 3s2 3p6 3d10 4s1

define ionisation energy

minimum amount of energy required to remove 1 mole of electrons from 1 mole of atoms in the gaseous state

write first ionisation energy equation for sodium

Na (g) -> Na+ (g) + e-

is ionisation endo or exothermic

endothermic, it requires energy = positive value

how does shielding effect ionisation energy

more electron shells between positive nucleus and negative electron = less energy required to remove,

weaker electrostatic attraction

3 factors that affect ionisation energy

shielding, atomic size, nuclear charge

how does atomic size impact ionisation energy

bigger the atom the further away the outer electrons are from the nucleus, attractive force between electrons and nucleus reduces = easier to remove electron

how does nuclear charge impact ionisation energy

more protons in nucleus = bigger attraction between nucleus and outer electrons = more energy required to remove the electron

define successive ionisation

removal of more than 1 electron from the same atom

define second ionisation energy

energy needed to remove one mole of electrons from one mole of +1 gaseous ions, producing one mole of 2+ gaseous ions

reasons for jumps in ionisation energy

removing electrons from shells closed to the nucleus

why is there an increase in successive ionisation energy

removing an electron from an increasingly more positive ion

1st ionisation energy trend down a group

decreases

why does ionisation energy decrease down a group

atomic radius increases, outer electrons are further from the nucleus, attractive force is weaker = less energy required

- shielding increases, more shells = attractive force is weaker = less energy required

1st ionisation trend across a period

increases

why does ionisation energy increase across a period

nuclear charge increases as protons increase, increasing nuclear attraction

shielding doesn't change

atomic radius slightly decreases as atom is compressed from increased nuclear charge = stronger attraction

exceptions in period 3

decrease at aluminium = evidence for sub shells

- was not explained by Niels Bor atomic model

- slight decrease from P to S

how is a decrease at aluminium evidence for atoms having sub shells

decrease of 1st ionisation energy across period 3

- outer electron sits at a higher energy sub shell, further from the nucleus compared to magnesium = decrease

- magnesium: outer electron in 3s

- aluminium: outer electron in 3p

what is the decrease at sulfur from phosphorus evidence for

electron repulsion

why does ionisation energy slightly decrease between phosphorus and sulfur

both have outer electrons in 3p, shielding is the same

- sulfur: 3p4 (1 pair of electrons in a sub shell)

- phosphorus: 3p3 (electrons = unpaired)

- electrons repel, so less energy is needed to remove an electron from an orbital with 2 in than 1

why do electrons pair up with opposite spins

so the atom is as stable as possible

what is produced if electron spins are unpaired and unbalanced

natural repulsion = unstable,

atoms may take a different arrangement to improve stability