C2 Topic 1

C2 Topic 1

1. structure of the atom

   • the nucleus is in the middleof the atom
     • contains protons amd neutrons
       • proton relative mass: 1 relative charge: +1
       • neutron relative mass: 1 relative charge: 0
     • nucleus has a overall positive charge as protons are positively charged and neurons have no charge
   • electrons move around the nucleus
     • electron mass: 1/2000 relative charge: -1
     • the number of neutons equal the number of protons
   • neutral atoms have NO charge

2. elecron shells

   • electrons occupy shells
   • the lowest energy levels are allways filled first
     • the one closet to the nucleus
   • a certain number of electrons are allowed in each shell
     • 1st shell: 2 2nd: 8 3rd: 8
   • atoms are happier when they have full shell electrons
     • In most atoms the outer shell is not full and this makes the atom want to react
   • electronic configuration
     • the proton number is the same as electrons
       • example: argon proton no. 18 electron no. 18 follow electron shell rules 2.8.8

3. elements

   • elements consist of one atom only
   • each element has a different number of protons
   • each element has a atomic no. and a mass no.
     • to find the neutrons in a atom subtract the atomic no. from the mass no.
       • example: oxygen mass no. 16 atomic no. 8 16-8=8 8 electrons

4. isotopes

   • isotopes are different atomic forms of the same element with the SAME no. of PROTONS and a DIFFERENT no. of NEUTRONS
   • relative atomic mass (Ar)
     • uses the relative mass of an element and the relative abundance for each isotope
       • relative abundance: how much there is of each isotope compared to the total amount of element in the world
     • to work it out: 1st - multiply the mass of each isotope by its relative abundance. 2nd - add those together 3rd - divide that by the sum of the relative abundances

5. periodic table (pt)

   • history
     • in the 1880's scientists first put the elements in order of their atomic mass
     • in 1869 Dimitri Mendeleev arenged the elements in groups acording to their properties
       • he found that he had to leave gaps to make this work (un discovered elements)
         • in the gaps Mendeleev even predicted some properties of undiscovered elements
           • Since then new elements have been discoverd which fit into the gaps
   • over the years the periodic table has been refind to what we know it as today
   • metals and non-metals are on opposite ides of the pt
   • the pt is arranged in periods and groups
     • periods - the rows
       • the elements are arranged in order of increasing atomic number
       • the period number is the same no. of electron shells example: row 2 have 2 electron shells
       • along the periods the elements change
     • groups - the columns
       • elements in groups have similar properties
         • this is because they have the same no. of electrons in their outer shell
       • the group no. is equal to the no. of electrons in their outer shell
       • the properties of elements often gradually go down the group