topic 1 - atomic structure and bonding

• Atoms have an approximate diameter of 1x10-10. They are tiny.
• Even with the most complex microscope we still cannot see inside of atoms.
• We cannot know for sure if our modern model of atomic structure is accurate but we have built up evidence throughout the years to support specific models.
• Our knowledge and understanding developed in time with improvements in technology.
• Democritus


  420 BC, hypothesised that all matter was made up of tiny particles, hypothesised that matter could be cut up into smaller and smaller pieces until eventually you would only have a tiny particles left which would all be identical and couldn't be divided any further, named these particles Atomos
• John Dalton


  Towards the end of the 18th century, was a scientist part of a group of scientists doing experiments to investigate the breaking down of complex substances into smaller simpler substances and then the recombining of these simpler substances in different ways to make different complex substances, named these different complex substances compounds and the simpler substances elements, during the experiments, they recorded the masses of the compounds formed and discovered that the elements reacted consistently in the same relative proportions to form new compounds, concluded that the masses of individual particles were too small to measure accurately but they could be calculated using the measurements and observe actions of the compounds formed and the reacting ratios of the elements, 1803, shared his findings with the world and hypothesised that all elements were made of particles which all had identical mass specific to that element, described these particles as tiny, solid sphere like objects, his finding supported Democritus' theory that these particles were indivisible, named them atoms
• Henri Becquerel


  Proved John Dalton's theory that atoms were indivisible wrong by discovering radioactivity, his work showed that atoms released smaller particles from inside of themselves, proving that they weren't just solid indivisible particles but must contain smaller particles within
• JJ Thompson


  A year after Henri's discovery, was investigating the electrical conductivity of gases by passing narrow beams of gas particles through air in a tube containing electrically charged plates, his findings showed that no matter which gas was being tested the beam of particles would always bend towards the positively charged plates suggesting that the particles in the beam must be negatively charged as they were attracted to the positively charged plate, conducted further experiments using only hydrogen gas and his findings also proved that no only were the particles negatively charged but were also 200x smaller than hydrogen atoms, had discovered the first of the sub-atomic particles and named them electrons, hypothesised that as the negatively charged electrons were smaller and lighter than the atom, there must have been something else within the atom which was positively charged to prevent the electron leaving the atom and accounting for the rest of the mass, suggested that the positive charge was spread over the whole atom and the negatively charged electrons were embedded within it, The Plum Pudding Model was his model
• Ernest Rutherford


  Built on the work completed by Becquerel on radioactivity, discovered that atoms released 2 different types of radiators, alpha particles and beta particles, discovered that the alpha particles were small with a large mass and were positively charged, conducted a series of experiments firing the positively charged alpha particles at a sheet of gold foil a few atoms in thickness, concluded from these findings that atoms must contain a tiny concentrated area of positive charge in the centre which deflected the alpha particles (bc alpha particles are positively charged), named this area of positive charged the nucleus, also concluded that there must be lots of empty space surrounding the centre containing the electrons as the alpha particles were attracted towards the electrons and could pass through the empty space, suggested that the positive charge in the nucleus was due to the presence of small positively charged particles, named these the second sub-atomic particle to be discovered and named them protons, surmised that because atoms have no overall charge that the amount of positive and negative charge must be equal and so the number of protons and electrons must be equal
• Niels Bohr


  Worked with Rutherford on his development of atomic structure, previously, a physicist called Planck had been developing ideas about energy and how it could be used, built on Planck's ideas on energy and used them to try to develop an understanding of how electrons may be positioned within the atom, hypothesised that the electrons were attracted towards and surrounded by the atoms nucleus until an amount of energy was applied causing the electrons to move away from the nucleus, made a model with a central model and the electrons orbiting the nucleus in distinct energy shells, suggested the electron shells were at great distances from the nucleus which accounted for the empty space inside the atom, also suggested that the fullness of the energy shells dictated the reactivity of an atom

  
• James Chadwick


  Discovered the third sub-atomic particles and named it the neutron, studied under Rutherford, was examining the effects of Rutherford's gold foil experiments and discovered that during the experiments a third type of radiation was produced, deduced that this radiation was made of uncharged/neutral particles, which he named the neutron, experimented further and worked out that they had a mass of 1amu, concluded that these neutrons accounted for the additional mass of the atom and they must therefore be inside the nucleus with the protons, his theory of the atomic model described a central nucleus containing protons and neutrons and the electrons surrounding the nucleus
• Present Day Model


  The Quantum Mechanical Model, a modified version of the Bohr Model and Chadwick's Neutrons, this model describes a central nucleus contains protons and neutrons (nucleons) and electrons are found orbiting the nucleus in energy shells, protons have a relative charge of 1+ and a relative mass of 1, Neutrons have a relative charge of 0 and a relative mass of 1 and electrons have a relative charge of 1- and a relative mass of 1/2000