Chemistry - Module 4

Chemistry - Module 4

1. Atoms

   • nucleus - protons and neutrons - positive charge - almost whole mass of atom - miniscule compared to rest of atom
   • electrons - move around nucleus, negatively charged, tiny but cover alot of space, volume of orbit determines how big atom, virtually no mass, arranged in shells
   • protons - heavy - positive charge +1 - relative mass 1
   • neutrons - heavy, neutral - relative mass 1 - charge 0
   • electrons - tiny - negative charge - realtive mass 0.0005 - charge -1
   • number of protons equals number of electrons
   • if some electrons are added or removed, the atoms becomes charged and then is an ion
   • number of neutrons usually same as number of protons
     • number of protons decide what atom element is
   • elements all have different propertiees from each other due to differences in theor atomic structure

2. Line spectrums

   • some elements emit distinctive colours when heated
     • lithium Li - red flame
     • Sodium, Na - yellow/orange flame
     • potassium, K - lilac flame
     • identify metal in a compound
     • electrons get excited - release energy as light - wave lengths emitted can be recorded as a line spectrum
   • each element has a different pattern as wavelength and line spectrum
   • spectroscopy

3. periodic table

   • Döbereiner
     • 1800s - only knew relative atomic mass - known elements arranged in order of atomic mass
     • 1828 put elements into groups based on chemical properties - put into groups of 3s - triads - middle element of each triad had relative atomic mass that was average of other 2
   • Newlands
     • arranged elements in order of relative atomic mass - every 8th element had similar properties - listed know elements in rows of 7
     • newlands' octaves
     • pattern broke on 3rd row - left no gaps
     • 1865 - work ignored bc - groups didn't have similar properties , mixed up metals and non-metals, didnt leave any gaps
   • Mendeleev
     • 1869
     • put elements in order of atomic mass - left gaps for undiscovered elements with similar properties in same vertical groups - gaps predicted properties and when those elements were discovered they fit the pattern they confirmed his theory
   • increasing proton order - repeating patterns in the properties of elements
   • non metals left - metals right
   • elements with similar properties - columns
   • vertical columns - groups - group number - how many electrons in outer shell. exception of group 0 - 8 electrons
   • predict properties of other elements in group and also reactivity
     • group 1 increases as you go down - group 7 reactivity decreases as you go down
   • rows - periods
   • relative atomic mass - total number of electrons and protons. calculate number of neutrons by subtracting number of protons from ram

4. Electron shells

   • electrons always occupy shells
   • only a certain number of electrons are allowed in each shell - 1st - 2 - 2nd - 8 - 3rd - 8
   • atoms much happier with full outer shell - if not full - makes atom want to react

5. Ionic Bonding

   • ions are made when atoms gain or lose electrons - become charged
   • can be made from a single atom or a group
   • trying to get a full outer shell
   • group one elements all have 1 electron on outer shell - want to get rid of it
     • when grp 1 lose electron - form positive ions
   • group 7 elements have outer shells that are nearly full - want to gain electron to become full - become negative ion
   • oppositely charged ions are strongly attracted to each other
     • ionic bond
       • compounds formed between grp 1and 7 held together by ionic bonds - ionic compounds
         • ionic compounds form a giant lattice - each lattice forms a single crystal.
           • when molten or dissolved they conduct electricty - ions able to move
     • gain - negative
     • lose - positive

6. ions and formulas

   • charges in an ionic compound add up to 0
   • differnent ions have different charges

7. Group 1

   • alkali metals
   • litium, sodium, potassium, rubidium, caesium, francium
   • ONE outer shell electron - VERY reactive and similar properties
   • react to form similar compounds
   • shiny when freshly cut, but quickly react with oxygen in air and tarnish
   • as you go down - more reactive, higher density - atoms more mass, lower melting and boiling point
   • reaction with cold water - hydrogen gas
     • lithium, sodium, potassium react very vigorously - fizzy and move - produce hydrogen - small flame
       • squeaky pop
       • more violent more reactive
       • OH
   • reaction with chorine - salt
     • Cl

8. Group 7

   • halogens
   • chlorine, bromine, iodine
   • SEVEN outer shell electrons - very reactive, similar properties and form similar compounds to each other
   • halogens form diatomic molecules which are pairs of atoms
   • as you go down - less reactive - outer electrons are further from nucleus and additional electrons are attracted less strongly
     • have a higher melting and boiling point
   • all non metals with coloured vapours
     • fluorine - very reactive - poisonous yellow gas
       • chlorine - fairly reactive - poisonous dense green gas
     • bromine - dense poisonous orange volatile liquid - forms orange gas
     • iodine - dark grey crystalline solid or purple vapour
   • reactions with alkali metals - form salts - metal halides - less vigorous as you go down
   • reactions with iron - coloured solids - iron halides - less vigorous as you go down
   • displacement reactions - where a more reactive element displaces a less reactive element from a compound

9. labatory safely

   • oxidising - ring with flame ontop - provides oxygen which allows other materials to burn more fiercely
   • highly flammable - flame - catches fire easily
   • toxic - skull - can cause death by swallowing, breathing, absorbtion
   • explosive - bomb expolodly - can explode
   • corrosive - test tube and hands - attacks and destroys living tissues
   • alkali metals
     • reactive combust
     • water vapour - violent reaction - kept in oil
     • never use bare hands - sweat can react - corrosive
   • halogens
     • toxic
     • corrosive
     • poisonous
     • fume cupboard