Atomic structure and the periodic table

• Coarse (or dust) particles have a diameter between 1 × 10^-5 m and 2.5 × 10^-6 m.
• Soluble solids can be separated from a solution using crystallisation.
• JJ Thompson created the plum pudding model, in which electrons are scattered in a sea of positive charge.
• Ancient Greeks thought matter to be made of indivisible particles.
• Ernest Rutherford discovered the nucleus was small and positively charged by finding alpha particles went straight through a gold leaf and few deflected back.
• Neils Bohr deduced that electrons exist in shells.
• James Chadwick determined that the nucleus must contain neutrons as well as protons.
• Bottom number in the periodic table is the atomic number. This is the number of protons in the nucleus.
• The mass number is the top number in the periodic table and is the number of protons and neutrons in a nucleus.
• Elements were initially ordered according to atomic weight
• Dimitri Mendeleev swapped order of elements and left gaps for elements to be discovered.
• Columns are called groups and give the number of electrons in the outer shell.
• Non metals always accept electrons to form a full outer shell, and form negative ions.
• Metals always lose electrons to have an empty outer shell and form positive ions.
• Hydrogen can both lose and gain electrons.
• Alkali metals get more reactive as you get down the group, as electron is easier to lose.
• Halogens get less reactive down the group and increase boiling point.
• Noble gases are very unreactive.
• Metals form a lattice of ions surrounded by a sea of delocalised electrons. As electrons are free to move, they are good conductors of electricity.
• Democritus - atomic theory, indivisible spheres
• John Dalton - atomic theory, solid spheres and elements
• JJ Thomson - plum pudding model
• Ernest Rutherford - alpha scattering experience (gold) nuclear model (negative cloud surrounding positive nucleus)
• Niels Bohr - electron shells preventing collapse
• James Chadwick - neutrons
• Valence electrons - number of electrons in the outermost shell of an atom
• Dmitri Mendeleev created the first successful periodic table in 1869
• About 100 different elements
• Mixtures can be separated by physical processes like filtration, crystallisation, simple distillation, fractional distillation and chromatography.
• Atoms have a radius of 0.1nm (1x10-10m)
• The radius of a nucleus is less than 1/10,000 of the atom (about 1x10-14m)
• Mendeleev left gaps in his periodic tables for new elements
• Group 1 are alkali metals