atomic structure and the periodic table (1)

• atom


  smallest part of an element that can exist
• compound


  a substance made up of two or more atoms chemically joined
• element 


  a substance made up of only one type of atom
• ion 


  an atom or molecule that with an electric charge due to the loss or gain of electrons
• mixture 


  two or more elements not chemically joined
• first development of an atom


  tiny spheres that could not be divided
• plum pudding model (2nd development)


  discovered the electron- atom is a ball of positive charge with negative electrons embedded in it
• alpha particle scattering experiment(3rd development)


  mass of an atom was at the centre- nucleus- and that the nucleus was charged
• method of the particle scattering experiment

  a beam of alpha particles were aimed at very thin gold foil and their passage through was detected, some of the alpha particles were being repelled and deflected meaning they came back at different angles. this was due to the small concentration of positive charge in the atom, the nucleus
• neil bohr (4th development)


  suggested electrons orbit the nucleus at specific distances
• later experiments of the atom


  positive charge of any nucleus could be subdivided into a whole number of smaller particles, each having the same amount of positive charge - protons
• James Chadwick work


  provided the evidence to show the existence of neutrons within the nucleus
• atomic number


  the number of protons in an atom of an element
• relative charge of proton, neutron, electron


  proton= +1, neutron= 0, electron= -1
• mass number 


  the sum of the protons and neutrons in an atom
• relative mass of a proton, neutron and electron 


  proton=1, neutron=1, electron= very small
• isotopes


  atoms of the same element with different numbers of neutrons but the same number of protons and electrons
• relative atomic mass 


  ​An average value that takes account of the abundance of the isotopes of the element.
• elements in the periodic table

  elements in the same group have the same number of electrons in the outer shell
• Mendeleev


  left gaps in his periodic table for elements he thought hadn't been discovered yet, ordered his table in order of atomic mass
• metals 


  elements that react to form positive ions
• where are metals found on the periodic table


  to the left and towards the bottom
• non metals


  elements that form negative ions
• where are non metals found on the periodic table

  towards the right and top
• group 1- alkali metals


  single outer shell electron, react vigorously with water, react with oxygen to create an oxide, react with chlorine to make a white precipitate, the reactivity increases going down the group
• group 0 - noble gases

  8 electrons on their outer shell (full outer shell) , unreactive, boiling point increases as you go down the group
• group 7- the halogens 


  reactivity increases going down the group but melting point and boiling point decrease, they react with nonmetals to form covalent compounds, they react with metals to form ionic compounds
• transition elements compared to group 1


  harder and stronger, have higher melting points, higher densities, less reactive
• some transition elements examples


  manganese, iron, cobalt, nickel, copper
• properties of transition elements 


  ions with many different charges, form coloured compounds, useful as catalysts