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CHEMISTRY > atomic structure > Flashcards

atomic structure Flashcards

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1
Q

what did Dalton discover in 1803 ?

A
  • atoms are spheres + each element made from diff spheres.
  • atoms are indestructible/ indivisible
  • identical elements: same mass/chemical properties - diff elements: diff mass/chemical properties
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2
Q

what did J.J thompson discover in 1897? (plum pudding model)

A
  • atoms contained electrons, divisible into smaller particles + negative charge cancelled out by sphere of positively charged material
  • measured deflection of negative particles in cathode rays accurately, calculated mass + physical properties.
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3
Q

what did rutherford discover in 1909? (alpha particles scattering experiment)

A
  • the nucleus: concentrated on central region, positive charged atoms contained in nucleus , e- circulate the atom + kept apart: repulsion
  • atom mainly empty space made up a ‘negative cloud’
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4
Q

what did bohr discover in 1913?

A
  • a problem with rutherford model - cloud of electrons could collapse into positive nucleus
  • electrons orbit nucleus in energy levels with set distance + has fixed energy values - they are quantised!
  • studied emission spectra + produced explanations: einstein and planck
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5
Q

what did chadwick discover in 1932?

A
  • the neutron: no charge, same mass as proton
  • bombarded beryllium plate with alpha particles + produced uncharged radiation on other side of plate - placed paraffin wax disc (w hydrogen atoms) in path of radiation causing protons being knocked out of wax.
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6
Q

EXTRA - what did democritus discover ?

A
  • ‘atomos’ - atoms cannot be divided into anything further.
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7
Q

EXTRA: what did aristotle discover ?

A
  • matter made from 4 elements: earth, air, water, fire

-e.g - rain falls and air bubbles rise from water.

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8
Q

EXTRA: what did moseley discover ?

A
  • x-ray spectra of elements + related the frequencies to a number now known as ‘atomic number’
  • mass of protons accounted for half of mass of nucleus
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9
Q

what is the relative mass and charge for each subatomic particles?

A
  • electrons: relative mass = 5.45x10^-4, relative charge = -1
  • protons: relative mass = 1, relative charge = +1
  • neutrons: relative mass = 1, relative charge = 0
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10
Q

what does the atomic number (Z) tell us about an element?

A
  • the no. of protons in an atom (+ also electrons)
  • no. of protons = no. of electrons in a neutral atom - no electrical charge
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11
Q

what does the mass number (A) tell us about an element ?

A
  • total number of protons + neutrons in nucleus of an atom
  • mass number (A) = no. of protons (Z) + no. of neutrons (n)
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12
Q

define relative atomic mass, (Ar)

A
  • the average mass of an atom compared to 1/12 the mass of a carbon-12 atom.
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13
Q

what are isotopes of an element ?

A
  • diff forms of the same element - containing same number of protons but diff numbers of neutrons - almost same chemical properties: differ in mass so diff physical properties = rate of diffusion(depends mass) + nuclear properties: radioactivity
  • relative isotope mass - average mass of an atom of an isotope
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14
Q

how do you work out the weighted average ?

A
  • (mass of isotope x number) + (mass of isotope x number)
    —————————————————————
    total number
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15
Q

how many orbitals and electrons do these shell contain? 1s, 2p, 3s, 3d, 4s

A
  • 1s: 1 orbital, 2 electrons
  • 2p: 3 orbitals, 6 electrons
  • 3s- 1 orbital, 2 electrons
  • 3d: 5 orbitals, 10 electrons
  • 4s: 1 orbital, 2 electrons
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16
Q

what is the order of energies of sub- shells ?

A
  • 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f
  • (4s orbitals have lower energy than 3d so filled first + in ions: electrons in highest energy levels are lost first but when losing electrons- electrons lost from 4s before 3d)
17
Q

what is an orbital ?

A
  • a region around the nucleus that can hold up to 2 electrons
18
Q

what would be the relationship between 2 electrons in the same orbital in terms of their spins?

A
  • have opposite spin as repel each other as both negative: repulsion
19
Q

explain why chromium and copper does not fit the trend for electronic configuration.

A
  • both have one electron in its 4s orbital before filling 3d due to stability
  • chromium - 1s^2.. 3p^6, 4s^1, 3d^5
  • copper - 1s^2… 3p^6, 4s^1, 3d^10
20
Q

define relative molecular mass, Mr

A
  • the average mass of a molecule compared with 1/12 the mass of carbon-12 atom.
21
Q

what does the mass spectrum of an element show ?

A
  • accurate instrumental technique for relative atomic mass + relative abundance for each isotope.
  • uses carbon-14 dating, detecting illegal drugs, forensic science, space exploration.
22
Q

define Hund’s rule.

A

-states that single electrons occupy all empty orbitals within a sub-level before they start to form pairs in orbitals

23
Q

what are the 2 types of ionisation for a mass spec ? how do they differ ?

A
  • electron impact - high energy electrons fired at sample from electron gun (hot wire filament with current through it emitting electrons) - knocks off one electron from each particle to form 1+ molecular ions
  • electrospray - sample dissolved in volatile solvent (water/methanol) : injected through fine hypodermic needle as a fine spray into vacuum in ionisation chamber - high voltage applies to end of needle - particles gain a proton from solvent as they leave the needle = produce XH+ ions/+1 ions.
24
Q

when would you use the diff types of ionisation in a mass spec ?

A
  • electron impact - organic/inorganic molecules with a low molecular mass
  • electro spray- substances with higher molecular mass including biological molecules (proteins)
25
Q

1) describe the stage of IONISATION in a time of flight mass spec

A
  • sample of element vaporised + injected into mass spec where high voltage passed over chamber/ firing electrons at them (knocking electrons from outer energy levels: electron impact ionisation)
  • ionised into positive ions
26
Q

2) describe the stage of ACCELERATION in a time of flight mass spec.

A
  • positively charged ions accelerated by an electric field.
  • lighter ions accelerate faster than heavier ones - BOTH same kinetic energy
27
Q

3) describe the stage of ION DRIFT in a time of flight spec

A
  • ions enter the flight tube - ions w diff masses have diff time of flight
  • they drift with no electric field at the same speed they were travelling at .
28
Q

4) describe the stage of the DETECTOR/ ANALYSIS of a time of flight mass spec

A
  • detector - negatively charged plate: more ions but detector - bigger current
  • ions gain an electron when they hit the detector creating an electric current that can be detected
  • current is produced which is proportional to abundance of ions
  • ANALYSIS- current values used in combination with flight times = produce a spectra print-out with relative abundance of each isotope displayed
29
Q

define first ionisation energy (of an element)

A
  • the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
30
Q

define the second ionisation energy.

A
  • the energy required to remove the second electron (not both electrons ) from an atom.
  • (energy needed to remove one mole of electrons from one mole of 1+ ions in their gaseous state to form one mole of 2+ ions)
31
Q

what are the 3 factors that affect the ionisation energy?

A
  • atomic radius - radius between the nucleus and outermost electrons = as atomic radius increase the force of attraction between positive nucleus + outer electrons decreases
  • nuclear charge - greater no. protons = greater force of attraction between outer electrons + the nucleus
  • shielding - electrons in outer shell repelled by electrons in inner shells - reduces attraction between outer electrons + nucleus.
32
Q

describe the first ionisation energies of group 2 elements

A
  • first ionisation energies decreases - atomic radius increases, no. electron shells between outer electrons + nucleus increases and more outermost electrons highly shielded from attraction of nucleus.
  • decreases ,, ions get bigger ,, weaker attraction of ion to lost electrons
33
Q

describe the first ionisation energies of period 3

A
  • across a period, nuclear charge increases as no. protons increases = increases attraction between the nucleus + the electrons
  • atomic radius decreases across a period - increased nuclear charge + decreased atomic radius = outer electrons more attracted to nucleus so first ionisation energy increase .
34
Q

what is the general trends for first ionisation energies ?

A
  • sharp fall in ionisation energy between neon + sodium and between argon + potassium as electrons enter new shell
  • outer electron shielded from nuclear charge by electrons in inner shells
  • increase - ionisation energy for each sub-shell as nuclear charge increases + electrons attracted strongly.

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