F321 Definitions

Revision for the basics in F321



First Ionisation energy- The energy required to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions 

Factors effecting Nuclear Attraction:

1) Nuclear Charge

2) Electron sheilding

3) Nuclear Radius

Shell                                        Sub-shell                                          Total Electrons

1                                               1s                                                       2

2                                               2s, 2p                                                8

3                                               3s, 3p,3d                                          18

4                                               4s, 4p, 4d, 4f                                    32

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S orbital are spherical

P orbitals are a 3D dumbell shape

Sub Shell                  No. orbitals                      Maximum number of Electrons

      S                                   1                                                            2

      P                                   3                                                            6

      D                                   5                                                           10

      F                                   7                                                            14

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Ions: mg -> mg(2+) + e(2-)

Giant Ionic Lattice:

+ and - ions, brittle ,held together by electrostatic attraction, high melting and boinling point, doesn't conduct electricity when solid, conducts when molten as ions can move, soluble

Some elements can form multiple ions e.g. Fe(II) 2+ ions, Fe(III) 3+

1+ : Ammonuim NH4

1- : Hydroxide OH , Nitrate NO3 , Nitrite NO2 , Hydrogen carbonate HCO3 

2- : Carbonate CO3 , Sulphate SO4 , Sulphite SO3 , Dichromate Cr2O7

3- : Phosphate PO4

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SO4 (2-) Al (3+) = Al2(SO4(3

Covalent bond- bond formed over a shared pair of electrons

Lone  pair of electrons- any pair of electrons not invloved in bonding

Dative Covalent Bond- One atom supplies a lone pair of electrons to the covalent bond which are shared by an atom with a vacant orbital

Octet Rule:

Group 5- P, As

Group 6- S, Se, Te

Group 7- Cl, Br, I, At,

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Molecule              No. of electron pairs              Bond Angle              Name of Shape

BF3                      3                                                  120         Triagonal Planar

CH4                     4                                                  109.5          Tetrahedral

SF6                      6                                                  90                              Octtahedral

Lone pairs are more repulsive so as it is a more dense area of electrons therefore there it decreases the bond angle by 2.5 degrees for each pair

Molecule            Lone pairs                               Bond angle                Name of shape

NH3                    1                                                107         Pyramidal 

H20                     2                                                104.5                           Non Linear

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Molecules with multiple bonds 

Molecules with double bonds each double bond is treated as a bonded region

CO2 2 bonded regions 180 Linear

Electronegativity- is a measure of teh attraction of a bonded atom for a pair of electrons in a covalent bond

effecting factors : Atomic Charge  Atomic Radius  Electron Sheilding

When 2 atoms in a compound are identical the electrons are shared equally= non polar 

If there is a difference in charge it is called a permemant dipole

Symmetrical molecules are non polar as the dipoles cancell each other out 

Polar- difference in charge 

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Key Concept!

  • The greater the distance in electronegativity between the binded atoms the greater the dipole 
  • The more electronegative atom will take the the slighty negative charge

Down a group -More shells, more sheilding so electronegativity decreases

Across a period -Nuclear charge increases so electronegativity increases

Covalent -> Ionic

No difference between electronegativity =  non polar covalent bond

Small difference between electronegativity = polar covalent  

Large different between electronegativity = ionic as the electron is just taken

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Intermolecular forces are weak! 

Intramoleculcar forces are strong!

Bong type Relative Strength 

Ionic / Covalent                                   1000

Hydrogen                                            50

Dipole- Dipole                                      10

Van der Waals'                                     1    (caused by electron movement) 

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Van der waals forces are between all molecules/ atoms, whether they are polar or non polar. They cause all atoms to be attracted to each other

  • They are the weakest time of intermolecular force
  • Act between small temporarary dipoles in neigbouring molecules

ELECTRONS ARE ALWAY MOVING this means the electrons are likely to move more to one side than the other this creates a temporary dipole (instantaneous) These are destroyed and created constantly,

If a neighbouring molecule has a tempory dipole the +/- charge will cause electrons to attract or repell creating induced tempory dipoles. This can also set up a domino effect. 


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Effecting Factors:

Greator numbers of electrons = larger induced dipole = greater Van der Waals' forcesThe greater the points of contact = larger Van der Waals' forces

Boiling points increase due to more electrons which creates larger Van der Walals' forces also the larger forces make bonds harder to break needing more energy to break them.  (http://www.bbc.co.uk/schools/gcsebitesize/science/images/41_noble_gases.gif)

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Hydrogen Bonding : A strong Dipole- Dipole Bond

Attraction between :

  • An electron deficient hydrogen atom on one atom
  • A lone pair of electrons on a highly electronegative atom


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Properties on Hydrogen Bonding:

  • Why do icebergs float?- Ice is less dense than water. When water freezes the stronf hydrogen bonds hold together the water in a lattice shape .This lattice contains spaces between the molecules therefore less dense
  • How do pond skaters walk on water?- The extra intermolecular bonding of hydrogen bonds creates surface tension and viscosity. The surface tension allows pond skater to walk on water as they are practically walking on hydrogen bonds
  • The glue in DNA- They are responsible for creating the double helix shape.


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Metallic Bonding

The Giant lattice is held together by the attraction between + ions and - delocalised electrons 

High Melting/Boiling Points

Strong +/- attraction high tempertures are needed to displace protons and break bonds(http://www.bbc.co.uk/schools/gcsebitesize/science/images/gcsechem_60.gif)

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Good Cunductivity

Delcocalised elctrons carry the charge along the metal

Mallebility and ductility

Ductile: Stretchable Malleable: can be hammered into shape

Layers can move over each other and slide past each other

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