Atomic structure

Question 1

what model is used to describe the atom in radiography

Answer 1

the Bohr (planetary) model

Question 2

what is shown in this model:

Answer 2

electrons (-ve_ orbit the nucleus (+ve) at discrete energy levels often called shells

Question 3

inside the nucleus there are

Answer 3

protons (+ve charge) and neutrons (zero electric charge)

Question 4

therefore the overall charge of the nucleus is

Answer 4

positive

Question 5

electrons have a…

Answer 5

negative charge

Question 6

electron shells are often referred to as

Answer 6

k, l, m, n

depending on their distance (energy level) from the nucleus

Question 7

what is meant by the term ‘principal quantum number’ or ‘n’

Answer 7

their electron shell

e.g. K is 1, L is 2, M is 3 etc

Question 8

an electron shell cannot contain

Answer 8

more than 2n^2 electrons (where n is the principal quantum number)

Question 9

the outer shell cannot contain more than

Answer 9

8 electrons

Question 10

describe the symbol, location, mass and electric charge of: a proton

Answer 10

symbol= p
location=nucleus
mass=1.00
electric charge=+1

Question 11

describe the symbol, location, mass and electric charge of: neutron

Answer 11

symbol=n
location=nucleus
mass=1.00
electric charge=0

Question 12

describe the symbol, location, mass and electric charge of: an electron

Answer 12

symbol=e
location=orbiting the nucleus
mass= 1/1840
electric charge=-1

Question 13

what is the atomic number and where would you find it in relation to the element’s symbol

Answer 13

the number of protons in the nucleus

found below the element’s symbol

Question 14

what is the atomic mass number and where you find it in relation to the element’s symbol

Answer 14

total number of protons and neutrons in the nucleus

found above the element’s symbol

Question 15

what are isotopes

Answer 15

varieties of an element (also have the same atomic number) which have a different number of neutrons in their nucleus (and hence have a different mass number) Their physical and chemical properties may be different.

Question 16

what are radioisotopes

Answer 16

isotopes that have an unstable nuclei

Question 17

what the electron binding energy

Answer 17

amount of energy which must be absorbed by the electron to completely remove it from the atom.
It differs from shell to shell and element to element

Question 18

How does electron binding energy change as you go from the inner shell to the outer most shell

Answer 18

electrons in the inner shell have a higher electron binding energy than those in the outer shells, because they are closer to the positive charge of the protons in the nucleus and are more strongly attracted to it

Question 19

what is the unit for electron binding energies

Answer 19

kiloelectronvolts (keV)

Question 20

what happens during ionisation

Answer 20

when an electron in a shell has absorbed sufficient energy to overcome its binding energy, e.g. by irradiating it with x-rays, then the electron can escape from the atom, leaving behind a charge imbalance and a vacancy in its shell.

Question 21

before ionisation the atom is electrically neutral, afterwards…

Answer 21

the atom is positively charged an is referred to as a positive ion. there is now a ‘vacancy’ in one of its shells

Question 22

after ionisation, an electron moves in from the next shell to fill the vacancy, what does it emit?

Answer 22

a photon of electromagnetic radiation (emr), whose energy is equal to the difference in binding energies of the shells involved

Question 23

what is excitation

Answer 23

when an electron absorbs an amount of energy that is less than its binding energy. it is unable to be ejected from the atom, but can only be raised to a higher energy level, this is called excitation.

Question 24

what happens to atoms in an excited state

Answer 24

they are unstable and quickly return to the lower energy state with th emission of excess energy in the form of a photon of electromagnetic radiation, of energy equal to the difference in binding energy of the 2 shells involved in the transition

Question 25

what is the nuclear binding energy

Answer 25

the energy expended in keeping the nucleus together

Question 26

when is a nucleus said to be stable

Answer 26

when the binding energy is sufficient to keep the nucleus together

Question 27

what influences nuclear stability

Answer 27

the relative number of protons and neutrons

Question 28

nuclides with a large number of neutrons tend to be

Answer 28

unstable

Question 29

what happens when the nucleus becomes unstable

Answer 29

this is the basis of the phenomenon of radioactivity

Question 30

what is radioactivity

Answer 30

the emission of excess energy from the nucleus of an atom as it attempts to adopt a more stable state