Pure substances and atomic theory

• Pure subtance - form of matter that hace the same definite and unchanging chemical position that can be classified as elements or compounds.
• Elements - substance that are made up of only one type of atom.
• OXYGEN - is the most abundant element in the earth's crust.
• Compound - substance that are made up of more than one type of atom.
• Chlorine - a very poisonous green gas with intensely disagreeavle suffocating odor.
• Sodium -a soft metal that can be cut easily with table knife , it reacts violently to water.
• Mixtures - made up of two or more subtances that are physically combined.
• Homogeneous mixture - have only one phase, or have uniform appearance throughout any portions
• Solution - a homogeneous mixture of two or more subtances in variable composition.
• solute - which gets dissolved and the solvent which does the dissolving.
• mixture can be seperated by physical means include

  filtration, evaporation, sublimations , distillian , decantation, crystallization.

  
  

  chemical seperation methods include heating using electricity or light energy
• heterogeneous mixture - made up of more than one phase or of different parts can be seperated by physical means.
• Democritus - greek philosopher suggested world was made of two things empty space and atomos.
• John Dalton - proposed that all matter is composed of tiny particles called atoms.
• john dalton is the father of modern atomic theory he propsed that atoms are solid hard spheres like billiard balls.
• J.J thomson - discovered the electron he was the first scientist to show the atom was made of even smaller things.

  
  

  his plud pludding model

  
  

  he discovered the electorn by the use of cathode ray
• Eugen goldstein - he also used the cathode ray and discovered protons.
• Ernest rutherford - discoverd the atoms nucleaus by doing a gold foil experiment.
• the nucleus is a small dense core with a positive charge.
• Neils bohr - electrons are not attracted to the + nucleus and cluster around it.

  disaproved rutherford's plantetary model

  used the enery level model : electrons are arranged in circles around the nucleus ,each circle has a different energy.
• Niels Bohr proposed that electrons can only exist on certain energy levels (shells) around the nucleus, which correspond to specific distances from the nucleus.
• The Bohr Model shows how electrons orbit the nucleus at specific distances from the nucleus, known as shells or energy levels.
• Atom -smallest particle of an element that can exist alone.

  atom has two regions

  center of an atom

  protons and nuetrons

  electron cloud - are surrounding nucleus containinf electorns
• proton - positive charge found in the nucleus 1 atomic mass
• neutron - neutral charge found in the nucleus
• electron -negative charge - mass very small
• Atomic number - number of protons in nucleus

  the number of nucleus detemines indentity of the element
• mass number - number of protons + nuetrons

  units are g\mol
• isotopes - atoms of the element with varying number of nuetrons
• ions- sometimes atoms will gain or lose electrons and form IONS.

  when an atom gains electrons it becomes NEGATIVE

  when an atom LOSES electrons it becomes POSITIVE.
• CATION- positive ion
• ANION - a negative ion
• atoms - are basic building blocks of matter.
• electron cloud - electrons orebit the nucleus
• nucleus or core - protons and nuetrons are found in the nucleus