atomic structure Flashcards

(29 cards)

1
Q

describe the process of nuclear fission

A

a neutron is absorbed by a (large) nucleus
the nucleus splits into two (smaller) nuclei
releasing energy (and gamma rays)
and (two / three) neutrons

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2
Q

describe the process of nuclear fusion

A

dslj

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3
Q

what is the count rate for a sample that records 769 counts in 60 seconds with a background radiation of 0.3 per second?

A

769/60 - 0.3

12.5

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4
Q

what is count rate?

A

counts per second ( recored by a detector eg geiger-muller tube )

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5
Q

what is the radius of an atom?

A

1 x 10^-10

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6
Q

the radius of a nucleus is less than ______

of the radius of an atom?

A

1/10,000

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7
Q

how is the energy level of an electron affected by its absorption of electro-magnetic radiation?

A

the electron will move to a higher energy level, further away from the nucleus

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8
Q

what is an isotope?

A

atoms of the same element but with a different number of neutrons

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9
Q

how is a mass number determined?

A

the total number of protons and electrons

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10
Q

how is an atomic number determined?

A

the number of protons in an atom

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11
Q

before the discovery of the electron how were atoms described?

A

as tiny spheres that cannot be divided

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12
Q

describe three features of the plum pudding model

A
  • the mass was evenly distributed within the atom
  • negative electrons were embedded, like plums in a plum pudding
  • the atom was a ball of positive charge
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13
Q

what were three conclusions from the alpha scattering experiment and why?

A

the mass is concentrated in a very small volume
- most of the particles went straight through so most of the atom is mostly empty space

the mass is concentrated in the centre
- very few came straight back so the mass must be in the centre

and the nucleus was positively charged
- because some were deflected at angles so there must be a concentration of positive charge ( as the positive alpha particles repel other positive charge )

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14
Q

who theorised the idea that electrons orbit the nucleus at different distance?

A

niels bohr

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15
Q

who discovered the neutron?

A

james chadwick

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16
Q

define radioactive decay

A

when an unstable nucleus emits radiation to become more stable

17
Q

what is the activity?

A

the rate at which a source decays

18
Q

what is activity measured in?

19
Q

what is the range in air of an alpha particle?

20
Q

what is the range in air of a beta particle?

21
Q

what is the range in air of a gamma wave?

A

a long distance

22
Q

how far can an alpha particle penetrate through materials?

A

not very far

a sheet of paper can absorb it

23
Q

how far can a beta particle penetrate through materials?

A

moderately far

absorbed by a sheet of aluminium or 2-3mm of lead

24
Q

how far can a gamma wave penetrate through materials?

A

very far

7m of concrete or several cm of lead

25
what is the ionising power of alpha, beta and gamma?
strongly ionising, moderately ionising and weakly ionising
26
what is the structure of an alpha particle?
two neutrons and two protons ( a helium nucleus )
27
what is the structure of a beta particle?
a high speed electron emitted from the nucleus - it is the extra mass when a neutron turns to a proton
28
what is the structure of a gamma ray ?
electromagnetic radiation
29
what is the half - life of a radioactive sample?
he time it takes for the number of nuclei of the isotope in a sample to halve,