1. ATOMIC STRUCTURE & PERIODICITY
1
, Particle Proton Neutron Electron
Relative charge +1 0 -1
Relative mass 1 1 1/1836
- An Isotope is an element whose atomic number is the same but the mass
number(number of neutrons) is different.
Relative Masses
- Relative Atomic Mass (Ar) of an element is the average mass of all the isotopes
of an atom relative to the mass of 1/12 of the mass of Carbon-12
- Relative Isotopic Mass is the mass of an isotope of an element relative to the
mass of 1/12 of the mass of Carbon-12
- Relative Molecular Mass (Mr) is the average mass of all the atoms in a molecule
relative to the mass of 1/12 of the mass of Carbon-12
- Relative Formula Mass is similar to Mr but is used for compounds with giant
structures
- Carbon-12 is used because it is a stable and abundant isotope
Mass Spectrometry
- Mass spectrometers can be used to determine all the isotopes present in a
sample of an element and their percentage or relative abundance.
1) Ionisation: sample of vaporised element passes through an electrical chamber
where an electron gun fires high energy electrons, knocking an electron off to
give a positive ion.
2) Acceleration: ions are accelerated through a
negatively charged electric field so they all
have the same kinetic energy.
3) Deflection: Ions are deflected by a magnetic
field into a curved path. Smaller mass /larger
no. of positive charge = more deflection.
4) Detection: beams of ions are detected
electrically
- Mass spectrum of monatomic elements:
- E.g. boron
- two isotopes; relative isotopic mass of 10
and 11.
- relative abundance:
Boron-10 23
Boron-11 100
- RAM: (23 x 10) + (100 x 11) / 123 = 10.8 to
3 s.f.
2
1
, Particle Proton Neutron Electron
Relative charge +1 0 -1
Relative mass 1 1 1/1836
- An Isotope is an element whose atomic number is the same but the mass
number(number of neutrons) is different.
Relative Masses
- Relative Atomic Mass (Ar) of an element is the average mass of all the isotopes
of an atom relative to the mass of 1/12 of the mass of Carbon-12
- Relative Isotopic Mass is the mass of an isotope of an element relative to the
mass of 1/12 of the mass of Carbon-12
- Relative Molecular Mass (Mr) is the average mass of all the atoms in a molecule
relative to the mass of 1/12 of the mass of Carbon-12
- Relative Formula Mass is similar to Mr but is used for compounds with giant
structures
- Carbon-12 is used because it is a stable and abundant isotope
Mass Spectrometry
- Mass spectrometers can be used to determine all the isotopes present in a
sample of an element and their percentage or relative abundance.
1) Ionisation: sample of vaporised element passes through an electrical chamber
where an electron gun fires high energy electrons, knocking an electron off to
give a positive ion.
2) Acceleration: ions are accelerated through a
negatively charged electric field so they all
have the same kinetic energy.
3) Deflection: Ions are deflected by a magnetic
field into a curved path. Smaller mass /larger
no. of positive charge = more deflection.
4) Detection: beams of ions are detected
electrically
- Mass spectrum of monatomic elements:
- E.g. boron
- two isotopes; relative isotopic mass of 10
and 11.
- relative abundance:
Boron-10 23
Boron-11 100
- RAM: (23 x 10) + (100 x 11) / 123 = 10.8 to
3 s.f.
2
