Bonding + structure (1)

• What is an ionic bond


  strong electrostatic forceof attraction between positive and negative ions
• What is a covalent bond?


  shared pair of electrons
• Which non metallic elements can share more than one pair of electrons forming multiple bonds?

  - H-H

  - O=O

  - N≡N
• How many electrons are involved in a H=h
• What is the octet rule?

  the tendency of atoms to gain a valance shell with a total of 8 electrons
• Why do some elements have more than 8 e- in their outer shell?

  - Have a vacant 3rd orbital

  -Which can occupy electrons

  - Therefore, most elements at end of period 3 can have more than 8 electrons
• Which elements are exceptions of the octect rule by having MORE than 8 electrons in its outershell?

  - S

  - P

  - Cl

  - Si
• Which elements are exceptions of the octect rule by having LESS than 8 electrons in its outershell?

  - B

  - Be

  - Al
• Why is boron triflouride (BF3) an exception to the octet rule and explain why?

  Boron triflouride (BF3)

  - Boron has 3 outer shell e-

  - Flourine has 7 outershell e-

  - 3 covalent bonds form: Each F has 8 outer e- HOWEVER, Boron has only SIX outershell e-
• What are examples of compounds that are exceptions to the octet rule and explain why?

  - Boron triflouride BF3

  - BeCl2

  -PF5

  - BH3

  - SO3

  - (A*) IF5

  - (A*) XeF4
• What are electron pairs which form bonds called in covalent bonding?

  bonding pairs
• What is a dative covalent bond ndicated by?

  An arrow pointing from the atom supplying the electrons to which the atom then shares them
• what should you always include in dative bond diagram?

  - Box with sign

  - Arrow to show where dative bond in EVEN if showing shape (EG H3O+ in pyramidal shape)
• What is a dative covalent bond?

  - A shared pair of electrons which have been provided by one of the bonding atoms ONLY

  -Occurs if one of the atoms possess a lone pair of electrons which can be donated to form a covalent bond
• What is the bond enthalpy?

  energy required to break a bond
• Units of bond enthalpy

  kjmol-1
• What is shape determined by?

  Number of electrion pairs in outer shell surrounding CENTRAL atom
• Electron pair repulsion theory points - shape is determined by..?: (3)

  - Number of e- pairs- electron pairs repel to become as far apart as possible-lone pairsof electronsrepel more stronglythanbonding pairs
• Using a dot and cross diagram, what 3 factors can be used to predict the shape of molecules and ions?

  - Number of pairs of outershell e- on central atom

  - Number of bonding pairs of e-

  - Number of ione pairs of e-
• Why do Ione pairs of electrons repel more than a bonded pair?

  - lone pair isslightly more electron densethan a bonding pair
• Non linear features:

  - No. of bonding pairs?

  - No. Ione pairs?

  - Bond angle?


  - BP = 2

  - IP = 2

  - Bond Angle = 104.5
• Pyramidal features:

  - No. of bonding pairs?

  - No. Ione pairs?

  - Bond angle?


  - BP = 3

  - IP = 1

  - Bond angle = 107
• Trigonal planar features:

  - No. of bonding pairs?

  - No. Ione pairs?

  - Bond angle?


  - BP = 3

  - IP = 0

  - Bond Angle = 120 degrees
• Tetrahedral features:

  - No. of bonding pairs?

  - No. Ione pairs?

  - Bond angle?


  - BP = 4

  - IP = 0

  - BA = 109.5
• Octahedral features:

  - No. of bonding pairs?

  - Bond angle?


  - BP = 6

  - Bond angle = 90
• How to determine shapes by counting electrons?

  Step one:Work out how many electrons on the central atom using the periodic table.

  Step two:Add one electron for each single covalent bond formed to the central atom.

  Step three:If the molecule is charged, add one electron for each negative charge. Subtract oneelectron for each positive charge.

  Step four:Divide this number of electrons by 2 to give the number of electron pairs; this givesthe basic shape.

  2 pair = linear 180o3 pairs = trigonal planar 120 o4 pairs = tetrahedral 109.5o6 pairs = octahedral 90 o

  Step five:Modify this basic shape if lone pairs are present (by comparing step 2 and 4),reducing the bond angle by 2.5ofor each lone pair.
• If a question asks to:

  - name the shape

  - state the bond angles

  - explain the shape of a molecules

  
  

  How should you structure your answer? especiallly if there is an ione pair


  NAME OF SHAPE- Has this shape because...- Has [x] bonding pairs- Has [y] electrons pairs to become as fair apart as possible, forming a bond angle of [w degrees]- (IF IONE PAIR)"Lone pairs of electrons repel more strongly than bonding pairs"