periodic table

• in the early 1800s elements were arranged by...

  atomic weight
• Newlands' Law of Octaves

  - arranged in increasing order of atomic mass

  - every eighth element shares common properties

  - no gaps were left

  - mixed up metals and non-metals
• why was Newlands' Law of Octaves not accepted

  - some elements were sharing a space

  - no gaps for undiscovered elements

  - non metals and metals were mixing

  - properties started to become inconsistent as atomic number increased
• Newlands' Law of Octaves diagram

  
• Mendeleev's periodic table


  - Russian chemist (1869) - elements arranged in order of increasing atomic mass

  - some elements were rearranged to fit into groups

  - groups were elements with similar properties

  - 63 Elements known at this time

  - gaps were left for elements Mendeleev thought would be discovered in the future
• why was Mendeleev's periodic table not accepted at first

  - the increase in atomic number was irregular

  - there was gaps present
• elements Mendeleev predicted


  - scandium

  - gallium

  - germanium
• how did Mendeleev predict the properties of undiscovered elements

  by looking at the chemical properties and physical properties. For example, state, melting point, conductivity, etc. he was able to notice holes in the patterns and predict that there were elements that had not yet been discovered that would fill those holes
• why was Mendeleev's periodic table widely accepted?

  because elements with properties predicted by Mendeleev were discovered, filling the gaps in his table
• Mendeleev's periodic table diagram

  
• modern atomic table


  - 118 elements

  - ordered in increasing atomic (proton) number

  - organises elements into groups (columns)

  - group numbers say how many electrons are in the outer shell

  - groups have similar properties

  - rows are called periods, each new period represents another full shell of electrons

  - metals (left) and non-metals (right) and organised
• modern periodic table diagram

  
• metals


  - good conductors of electricity/heat

  - malleable and ductile

  - shiny

  - high melting/boiling points

  - high density

  - form positive ions when they react
• most elements are...

  metals
• metallic bonding


  the chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons
• how do metals conduct heat/electricity?

  delocalised electrons in the metals can carry electrical charge through the structure
• non-metals


  - low conductivity

  - not ductile or malleable

  - dull

  - low melting/boiling points

  - low density

  - do not generally form positive ions when they react
• group 1 elements


  lithium, sodium, potassium, rubidium, caesium, francium
• group 1 elements are called alkali metals because...

  when they react with water, group 1 elements form metal hydroxides which are alkaline (with a pH above 7)
• group 1 element trends going down the table

  - increasing reactivity

  - decreasing melting/boiling point

  - higher relative atomic mass
• group 1 element properties

  - soft (they can be cut with a knife)

  - shiny

  - relatively low melting points

  - low densities (lithium, sodium and potassium can float on water)

  - very reactive

  - can conduct heat/electricity
• why are group 1 elements so reactive?

  only having one electron in the outer shell means it is more easily lost, so they readily form 1+ ions
• why do group 1 metals get more reactive as you go down the group?

  as the atomic mass increases, the electrostatic forces of attraction between the nucleus and outer electron gets weaker as they become further away because of shielding
• why do the melting/boiling point of group 1 elements decrease down the table?

  increasing atomic radius means the distance between the bonding electrons and the positive nucleus gets larger and reduces the overall attraction between the two, lowering melting and boiling points
• electronegativity


  a measure of the tendency of an atom to attract a bonding pair of electrons
• shielding


  shielding refers to the core electrons repelling the outer electrons, which lowers the effective charge of the nucleus on the outer electrons
• with non-metals, group 1 elements form ...

  ionic compounds by losing their electron
• group 1 element reaction with water

  - vigorous reaction

  - reaction gets more vigorous going down the group

  - produces hyrdrogen gas

  - produces metal hydroxides (salts that dissolve in water to produce alkaline solutions)

  - the amount of energy given out increases down the group
• group 1 element reaction with chlorine

  - vigorous reaction when heated in chlorine gas

  - reaction gets more vigorous going down the group

  - forms metal chloride salts
• group 1 element reaction with oxygen

  - forms metal oxide

  - different types of oxide formed depending on the group 1 metal
• differences between group 1 and transition metals

  - group 1 metals are much more reactive

  - group 1 metals are less dense, strong and hard

  - group 1 metals have lower melting/boiling points
• transition metals


  elements that form a bridge between elements on the left and right sides of the periodic table (groups 3 - 12)
• transition metal properties


  - good conductors of heat/electricity

  - very dense

  - strong

  - malleable

  - shiny

  - can have more than one ion

  - colourful ions/compounds

  - make good catalysts

  - less reactive than alkali metals
• group 7 elements


  fluorine, chlorine, bromine, iodine, astatine
• group 7 elements are called halogens because...

  the word halogen means 'salt forming' compounds. since all halogens have 7 electrons in their valence shell, they react rapidly with metals to form salts
• group 7 element trends going down the table

  - decreasing reactivity

  - increasing melting/boiling point

  - higher atomic mass

  - become darker
• group 7 element properties

  - very reactive

  - low melting/boiling point

  - poor conductors

  - dull and brittle (as solids)

  - non-metals

  - coloured vapour

  - soluble in water

  - each molecule is made up of a pair
• why are group 7 elements so reactive?

  only need to gain 1 electron to have full outer shell, so they readily form 1- ions
• why do group 7 metals get less reactive as you go down the group?

  as the atomic mass increases, the amount of electron shielding increases, meaning that the electron is less attracted to the nucleus
• why do the melting/boiling point of group 7 elements increase down the table?

  the atoms increase in size, as they gain extra electron shells, and the intermolecular forces become stronger. more energy is required to break these forces, thus there are higher melting and boiling points as you go down the group