5.1 Atomic structure and the periodic table

• Atoms make up all substances and are the smallest part of an element.
• Element is a substance that is made up of only ONE type of atom and cannot be broken down chemically
• Compound is a substance made up when 2 or more elements are chemically bonded together
• Proton: found in nucleus of an atom, has a positive charge, Relative change of +1 and relative mass of 1
• Neutron: found in the nucleus of an atom, relative charge of 0 and relative mass of 1
• Electron: orbiting around the nucleus, found in the outer shell of the nucleus, a relative charge of -1 and relative mass of almost 0
• Mixture: A substance made up of two or more elements or compounds that are NOT chemically combined
• Mixtures can be separated by techniques such as filtration, crystallisation, simple and fractional distillation and chromatography
• Filtration: separates INSOLUBLE SOLIDS from SOLUBLES. Example: separating sand from water where sand is left in the filter paper
• Crystallisation: separates SOLUBLE from SOLVENTS eg salt from water. Sample's heated in crystallising dish, heating stops when crystals are formed.
• Simple Distillation: separates LIQUID from SOLUTION, solution is heated until solution with lowest boiling point evaporates, vapour's cooled and condensed.
• Fractional Distillation: separates MIXTURES OF MISCIBLE LIQUIDS USING THEIR BOILING POINTS. Eg can separate ethanol from water and as ethanol has the lowest boiling point it is separated first
• Chromatography: separates SMALL AMOUNTS OF SOLUBLE SUBSTANCES FROM SOLVENTS. Eg different food colourings in food dyes. Pure substance: only ONE spot produced.
• 1803: John Dalton - 'atomic model' described it as a billard ball, tiny balls that cannot be divided.
• 1897: J.J Thomson discovered the electron, which is a negatively charged particle - 'Plum Pudding Model', negative electrons embedded in a ball of positive charge.
• 1909 - Geiger, Marsden and Rutherford discovered the nucleus through the alpha scattering experiment
• Alpha scattering experiment - Alpha particles fired through gold leaf, predicted that particles would fly straight through. Results: some reflected back as they collided with +ve nucleus at the centre, MASS IS CONCENTRATED AT CENTRE OF THE ATOM.
• 1913: Niels Bohr - electrons orbited at specific distances from the nucleus
• James Chadwick showed existence of neutrons in the nucleus
• Number of electrons = number of protons
• Atoms radius is 0.1nm (1x10^-10m)
• Radius of the nucleus is less than 1/10000 of an atom
• Mass number is at top of element, atomic number is at bottom of element
• number of protons + neutrons = mass number
• Isotopes: atoms of the same element that has different number of neutrons
• Elements in periodic table are arranged in order of increasing atomic number. so that elements with similar properties are in groups
• Groups = columns
• Rows = periods
• John Dalton- Arranged based on atomic mass, pictured symbols
• John Newlands- atomic mass, noticed every 8th element has similar properties, the law of octaves, presumed all elements were discovered, put metals and non-metals in the same group