2.1 Atomic Structure and Isotopes

Atoms of the same element with different numbers of neutrons and different masses. Most elements are made up of a mixture of isotopes

Mass number (A) Chemical symbol Eg. Au Atomic number (z)

No. Different isotopes of the same element have the same number of electrons and the number of neutrons has no effect on reactions thus they react similarly

Small differences in physical properties Higher mass isotopes with a higher melting point, boiling point and density BUT chemical reactions are the same

Used to control processes in nuclear reactors H2O molecules nearly all contain the Hydrogen-1 isotope but in heavy water, D2O, all molecules contain the Hydrogen-2 (deuteurium) isotope D2O has a greater density than H2O, higher melting point and higher boiling point

A charged atom The number of electrons is different from the number of protons

A positive ion, atoms with fewer electrons than protons, thus have an overall positive charge

A negative ion, atoms with more electrons than protons, thus have an overall negative charge

…with their overall relative charge Eg. Mg2+