Discovery of the atom Flashcards

Question

absorption spectrum

Answer 1

black lines on coloured background energy is absorbed from EM radiation continuum to promote an e- from ground state -> excited state

Answer 2

frequency/energy (transitions = quantised i.e. involve fixed amounts of energy)

Answer 3

couldn't account for line positions on emission/absoption spectra (classical model = when everything is known + defined)

Answer 4

[Neils Bohr, 1913] e- travel in circular orbits around nucleus e- hend in orbitals by attractive electrostatic forces within the nucleus

Answer 5

each orbit = fixed / quantised zero energy = taken as the point where e- is removed (∴ energy levels all lower than 0) lowest energy state - n = 1 (closest to nucleus)

Answer 6

Rutherford = predicted unstable atoms whereby e- lose energy as they travel (they should collapse in nucleus) Bohr = orbits have specific energies + e- can only gain or lose energy by changing orbit

Answer 7

1. worked well for hydrogen 2. explained the Rydberg formula for the emission lines of the H spectrum 3. quantum numbers + quantinisation introduced orbits with fixed energies

Answer 8

1. useless for anything except hydrogen 2. didn't explain why only certain orbits were allowed

Answer 9

radius of hydrogen = 0.529 A (= 1r)

Answer 10

1924 all matter had wave-like properties (formula relates matter to its wave) led to amended version of Bohr model with e- moving in a wave-like motion about the nucleus each e- orbital was considered to be a fixed number x wavelength

Answer 11

1925 shone e- beam at nickel crystal + recorded pattern pattern had areas of light + dark due to constructive/deconstructive interference of e- beam = only relevant to waves = diffraction pattern able to observe this due to wavelength of e- beam was close to spacing between nickel atoms [Conclusions] 1. e- have both particle and wave-like properties (= wave-particle duality) 2. classical model (certainty) replaced with probability/likelihood

Answer 12

objects that exhibit wave-like properties, one cannot measure their position AND momentum at same time Heisenberg determined lower limit to uncertainty = Planck's constant (h/4π)

Answer 13

based on electron particles moving in a wave-like motion

Answer 14

[𝚿] = a mathematical function that varies with position

Answer 15

used to determine energy levels for e- uses idea of an e- acting as a wave that alters with position

Answer 16

1. can only be used for 1-electron systems where it gives all energy levels possible for that electron 2. 𝚿 not measurable

Answer 17

an interpretation for SWE whereby 𝚿 could be related to a measurable quantity, 𝚿^2 equates to electron density for each 𝚿, SWE treats e- as wave that is delocalised ∴ one cannot say exactly where an e- is located at any given time possible to calculate probability of an e- being in certain volume of space

Answer 18

electron density per unit volume take small vol. of space 𝜏 d𝜏 = how e- density varies as one moves through space in small volume amounts (= get orbital shapes)

Answer 19

when R(r) = 0

Answer 20

when [Y(θ,Φ) = 0]

Answer 21

electron density at specific point in space as a function of distance (r) from the nucleus only i.e. probability of finding electron at a specific point

Answer 22

doesn't take into account amount of space available for the e- (rdf = more useful)

Answer 23

probability of finding an electron in a spherical shell of thickness (dr) at a distance (r) around the nucleus

Answer 24

[4πr2R(r)2) = most probable distance (r) from the nucleus of finding an e-

Answer 25

rdf(max) 2s > 2p (node in 2s) 2s penetrates 2p orbital (2s e- can get closer to nucleus than 2p e-) closer to nucleus an e- can get, the lower the energy will be

Answer 26

distance increases

Answer 27

represents 95% probability of where electron density is located for a given orbital

Answer 28

approximation can be viewed as the product of the wavefunctions from each single electrons (based on those for hydrogenic species)

Answer 29

e- enter and fill lower-energy orbitals before filling higher-energy orbitals

Answer 30

no 2 e- in same atom can be in same quantum state (i.e. no 2 electrons can have same set of 4 quantum numbers)

Answer 31

when degenerate, electrons will enter orbitals singly + only pair up when orbitals are half-full avoids e- repulsion and maximises exchange energy (K) - higher K = more stable

Answer 32

4s orbital has lower energy than 3d - when ionised, 4s electrons lost first

Answer 33

transition metals only populate outermost s-orbitals in their elemental forms e.g. Ni2+ electronic configuration = [Ar] 3d8 and not [Ar] 3d6 4s2 in compounds, s electrons

Answer 34

predicted = [Ar] 4s2 3d4 actual = [Ar] 4s1 3d5 actual = more exchange energies = more stable

Answer 35

in all atoms, there are attractive forces between e- and nucleus in atoms with >1 e-, there is repulsion to consider e- repulsions screen an e- from full nuclear charge (Z) 3d > 3p > 3s in terms of screening = effective nuclear charge (Zeff) whereby Z is reduced by S (screening)

Answer 36

increases for a given PQN the increase in Z is not cancelled out by the addition of another e

Answer 37

1/2 internuclear separation of neibouring atoms of same element in a molecule

Answer 38

1/2 the experimentally determined distance between nuclei of nearest neighbouring atoms in the solid state

Answer 39

measure of ion size - related to distance between neighbouring cations + anions

Answer 40

[increases] due to increase in PQN increase in radial nodes rdf max moves further from nucleus as 'n' increases

Answer 41

[decreases] Zeff increases - pulls e- cloud closer to nucleus rise to f-block contraction then d-block contraction f-orbitals = poor screeners (diffuse) -> elements with Z from 57 to 71, there is a greater than expected decrease in radii d-block => net effect; although 4d > 3d, the poor screening effect of f-orbitals means that 4d/5d elements in the same group have similar radii i.e. Ti < Ze ~ Hf

Answer 42

1/2 internuclear distance of closest approach between 2 atoms of the same type in different molecules

Answer 43

energy change on removing an electron from an atom to infinite distance in the gas phase units = ev eqns: 1st ionisation energy = M -> M+ + e- 2nd ionisation energy = M+ -> M2+ + e-

Answer 44

standard enthalpy change per mole to remove an electron from an atom in the gas phase

Answer 45

reverse of ionisation potential (also in gas phase) units = eV eqn: 1st electron affinity = M + e- -> M- NOTE - always check convention (i.e. if exothermic is +/-) by looking at Ae of F (which the gain of 1e- = exothermic) no thermodynamic conflict with electron gain enthalpy (exo = always -ve)

Answer 46

smaller radii as they have closed outer shells with smaller PQN fewer radial nodes rdf max = closer to nucleus

Answer 47

larger - e- being added to an already partially filled shell e- repulsion not offset by addition of proton to nucleus Zeff = smaller

Answer 48

reflects on increase in Zeff

Answer 49

P e- easier to remove (2p1 in B) than 2s e- in Be

Answer 50

easier to remove paired e- than unpaired e- (exchange energy not as diluted for N relative to O)

Answer 51

increases due to increase in Zeff

Answer 52

increases due to increase in PQN which casues outer e- to be screened from nuclear charges

Answer 53

electrostatic attraction between a cation and anion, formed from the transfer of electrons from one element to another occurs between elements with large electronegative differences ΔX > 2

Answer 54

electrons shared between atoms occurs between elements with small electronegativity differences ΔX < 2

Answer 55

electrostatic attraction between cations and mobile valence e-