3.1.3 Bonding - Physical

Question 1

3.1.3 Bonding

Question 2

Ionic bonding

Answer 2

• electrostatic attraction between oppositely charged ions in a lattice( giant )
• most ionic compounds dissolve in water - molecules water polar - attract +/- ions
• conduct electricity molten / dissolved - ions are free to move
• high melting points - strong electrostatic forces - lots energy required to overcome forces
• The formulas of compound ions, eg sulfate ( S04 2- , hydroxide ( OH) , nitrate( NO3 ) , carbonate ( CO3 2- ) and ammonium( NH4 + ) .

Question 3

construct formulas for ionic compounds.

Answer 3

1. Write the 2 ions - e.g. Ca2+ / NO3-
2. swap charges - Ca - , NO3 2+
3. Drop charges Ca , (NO3)2
4. Simplify to lowest whole number ratio

Question 4

Nature of covalent and dative covalent bonds

Answer 4

A single covalent bond - has a shared pair of electrons.- electrostatic attraction shared electrons, + nucleus

Multiple bonds contain multiple pairs of electrons.

• A co-ordinate (dative covalent) bond contains a shared pair of electrons with both electrons supplied by one atom.( 1 atom donates 2 electrons )
• represent with lines ( covalent) or arrows ( co-ordinate )

Question 5

Giant covalent structures

Answer 5

• Graphite - each carbon bond 3 times , 4th delocalised - layers slide , weak forces - delocalised electrons between layers, conduct electricity carry charge , low density , layers far apart - insoluble, strong covalent bonds - high melting point
• diamond- each carbon bonded 4 times - tetrahedral - conduct heat ( tightly packed / rigid ) , gemstones, high mp (strong c bonds ) , insoluble, no electricity conduct (no delocalised electrons )

Question 6

Shapes of simple molecules and ions- rules ‘

Answer 6

• Bonding pairs and lone (non-bonding) pairs of electrons , charge clouds that repel each other.
• minimise repulsion - pairs electrons in outer shell - arrange themselves far apart
• greatest ( lone - lone ) - (lone - bond ) - ( bond - bond ) repulsion
• add up bp and lp to find shape number / add electrons then divide by 2

Question 7

Shapes of simple molecules and ions- no lone pairs

Answer 7

• linear - e.g. BeCl2 - 2 bond pairs - 180 degrees
• Trigonal planar - e.g. BF3 - 3 bond pairs - 120
• Tetrahedral - e.g. CH4 - 4 bond pairs - 109.5
• Trigonal Bipyramidal - e.g. PCL3 - 5 bond pairs - 90,120
• Octahedral- SF6 - 6 bond pairs, 90

Question 8

Shapes of simple molecules and ions- with lone pairs

Answer 8

• Pyramidal - e.g.NH3 - 3 bp , 1Lp , 107
• Bent - e.g. H20 - 2bp , 2lp , 104.5
• Trigonal planar - 3 bp , 2lp , 120
• square planar - e.g. XeF4 - 90
• bond angles unchanged as 2 lone pairs repel equally from both sides

Question 9

Bond polarity- electronegativity

Answer 9

• Electronegativity as the power of an atom to attract the pair of electrons in a covalent bond.- use Pauling scale
• fluorine is most electronegative- further up/ right - the more electronegative

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Question 10

Bond polarity- polar bonds

Answer 10

• bigger difference in electronegativity - more polar bond is
• uneven distribution of charge leads to polarity (h20 , 2 delta + , 1 delta - )
• shared electrons with atoms of similar electronegative sit in middle - not polar , if polar electrons drawn to delta - atom
• if polar bonds arranged symmetrical, no polarity ( e.g. C02 - double bond , 2 delta -)

Question 11

Intermolecular Forces - van der waals

Answer 11

• induced dipole-dipole , weakest bonds , electrons move from one end to another of molecule- create temporary dipole
• 2 molecules are near by - s+ attract to s- - force of attraction
• iodine example , weak van der waals hold I2 , bigger atom ( e.g . Hydrocarbons) more van der waals , break forces when boiling liquid not covalent
• branched hydrocarbons weak van. der waals , lower bp , not close

Question 12

Intermolecular forces - dipole - dipole

Answer 12

• 2 weakest - involve interactions with permanent dipole - stronger - molecules have both dipole - dipole / van der waals
• exists between molecules with polarity - weak electrostatic forces
• tested using charged rod near polar liquid
• s+ attract to s-

Question 13

Intermolecular forces- hydrogen bonding

Answer 13

• strongest force, N, C , O, F only - e.g. ice - molecules further apart - less dense than water
  -HF higher bp than HCL - h bonding , more energy to overcome electrostatic forces
  Increase bp - hcl and hI , INCREASE mass molecule, bigger electron cloud , mor van der waals

Question 14

Metallic bonding

Answer 14

• metals giant metallic lattice
• • metal ions form , metals donate electrons, sea of delocalised
    -electrostatic force of attraction between + metal ion & - delocalised electrons
• good electrical / thermal conducts - delocalised electrons - carry charge (e) , KE (t)
• insoluble ( solid metal) - h mp

Question 15

The particle model

Answer 15

• solids - tightly packed , regular arrangement, high density , particles vibrate ,no compression
• liquids - tightly packed - random arrangements- high density - particle move freely , more energy , difficult to compress
• gases - random arrangements, low density , particles move freely , easy compressed, most energy