Chemistry Topic 1 – Atomic structure and the periodic table
ATOMIC STRUCTURE
1.1.1 Structure of the atom and isotopes
Particle Mass Charge Position 1897 – JJ Thomson, electrons.
Proton 1 +1 Nucleus 1917 – Ernest Rutherford, protons.
Neutron 1 0 Nucleus 1932 – James Chadwick, neutrons.
Electron 1/1840 -1 Energy levels
Rutherford is credited for suggesting atom has small core with bulk mass – nucleus.
Quantum shells – energy levels surrounding nucleus in which electrons exist.
C
12
Atomic number – number of protons
Mass number – number of protons + neutrons 6
1919 – Francis Aston invented mass spectrometer.
Used to discover that not all atoms of element have same mass.
Isotope – atoms of same element with different masses (neutrons are different).
1.1.2 Mass spectrometry and relative masses of atoms, isotopes
and molecules
Relative atomic mass (Ar) – weighted mean mass of atom of element compared to
1/12 of the mass of an atom of carbon-12; ionic/giant covalent compounds.
Relative isotopic mass – mass of individual atom of particular isotope relative to 1/12
of the mass of an atom of carbon-12; usually whole number.
Relative molecular mass (Mr) – average mass of molecule/formula unit, compared to
1/12th of mass of atom of carbon-12; simple molecules.
Calculating Ar of element from isotopic abundance
Ar = sum of (isotopic mass x isotopic abundance)
100
Mass spectrometer – measures masses of atoms and molecules.
Used for: C-14 dating, illegal drug detection, forensics, space exploration.
Produces +ve ions that are deflected by magnetic field according to mass:charge.
Mass spectra can be used to work out Ar of different elements.
x-axis gives mass:charge; y-axis gives abundance of ions/isotopic abundance – %.
Charge on ions is mostly +1 – can assume x-axis is simply isotopic mass.
Calculating Ar from graph
Ar = sum of (isotopic mass x isotopic abundance)
sum of isotopic abundances
Finding relative molecular mass Mr from graph
Molecular ion peak – peak with highest m/z ratio (furthest to right), M peak.
Its m/z ratio is equal to Mr.
Isotopes (13C) may cause small peak at M+1 which can be ignored when finding Mr.
ATOMIC STRUCTURE
1.1.1 Structure of the atom and isotopes
Particle Mass Charge Position 1897 – JJ Thomson, electrons.
Proton 1 +1 Nucleus 1917 – Ernest Rutherford, protons.
Neutron 1 0 Nucleus 1932 – James Chadwick, neutrons.
Electron 1/1840 -1 Energy levels
Rutherford is credited for suggesting atom has small core with bulk mass – nucleus.
Quantum shells – energy levels surrounding nucleus in which electrons exist.
C
12
Atomic number – number of protons
Mass number – number of protons + neutrons 6
1919 – Francis Aston invented mass spectrometer.
Used to discover that not all atoms of element have same mass.
Isotope – atoms of same element with different masses (neutrons are different).
1.1.2 Mass spectrometry and relative masses of atoms, isotopes
and molecules
Relative atomic mass (Ar) – weighted mean mass of atom of element compared to
1/12 of the mass of an atom of carbon-12; ionic/giant covalent compounds.
Relative isotopic mass – mass of individual atom of particular isotope relative to 1/12
of the mass of an atom of carbon-12; usually whole number.
Relative molecular mass (Mr) – average mass of molecule/formula unit, compared to
1/12th of mass of atom of carbon-12; simple molecules.
Calculating Ar of element from isotopic abundance
Ar = sum of (isotopic mass x isotopic abundance)
100
Mass spectrometer – measures masses of atoms and molecules.
Used for: C-14 dating, illegal drug detection, forensics, space exploration.
Produces +ve ions that are deflected by magnetic field according to mass:charge.
Mass spectra can be used to work out Ar of different elements.
x-axis gives mass:charge; y-axis gives abundance of ions/isotopic abundance – %.
Charge on ions is mostly +1 – can assume x-axis is simply isotopic mass.
Calculating Ar from graph
Ar = sum of (isotopic mass x isotopic abundance)
sum of isotopic abundances
Finding relative molecular mass Mr from graph
Molecular ion peak – peak with highest m/z ratio (furthest to right), M peak.
Its m/z ratio is equal to Mr.
Isotopes (13C) may cause small peak at M+1 which can be ignored when finding Mr.
