4.3 Covalent structures

Question 1

Creating Lewis structure

Answer 1

Question 2

Define coordinate/dative bond

Answer 2

COORDINATE/DATIVE BOND: bond formed between two atoms where both the e in bond originate from the same atom (donates e pair for a bond)

Question 3

Exceptions to the octet rule

Answer 3

Be and B - stable without octet - incomplete octet - electron deficient molecules

Question 4

Coordinate compound formation

Answer 4

Electron deficient molecules - likely to accept an e pair - formation of coordinate compound

Question 5

VSEPR theory

Answer 5

VSEPR: used for predicting molecule geometry - because e in the same e pair carry the same charge they repel each other, so they spread tehmselves as far as possible

electron pair => electron domain (lone pairs and in bonds)

• repulsion applies to electron domains
• total number of e domains around the central atom dtermines geometetrical arrangement of e domains
• shape of molecule is dteermined by bond angles
• non-bonding e pairs are of higher conc of charge - cause higher repulsion than bonding e

Question 6

geometrical shapes of molecules

Answer 6

• linear
• trigonal planar
• bent/v-shaped
• tetrahedral
• trigonal pyramidal
• see - saw
• T-shaped
• square planar
• square pyramidal
• octahedral

Question 7

Overall molecule polarity

Answer 7

Question 8

Define delecolaised e

Answer 8

DELOCALISED e: bonding e which are not confined to one location, they are shared between several bonding positions

Delocalisation of e provides stability for molecules

Question 9

Define resonance structure

Answer 9

RESONANCE: ability of a molecule to move delocalised e between different bonding places

Resonance structure - resonance hybrid

Question 10

Resonance in benzene

Answer 10

Question 11

Giant covalent structures

Answer 11

Allotropes of carbon: diamond, graphite, fullerene

Question 12

Define allotropy

Answer 12

ALLOTROPY: property of an element to come in different froms in the same physical state

O₂ and O₃ - both gas, different compounds

Question 13

Graphene

Answer 13

Graphene: new from of C:

• new conductive materials
• graphene transistors better than Si transistors
• touch screen - flexible but unbreakable
• toring charge - replace batteries
• solar panels - light and flexible but strong

Question 14

Define nanotechnology

Answer 14

NANOTECHNOLOGY: study which deals with atomic scale manipulations of matter

development of graphone - adding H to graphene

Question 15

Si bonding specialty

Answer 15

Si also forms 4 bonds like C - SiO₂ - similar structure to diamond - tetrahedrals

• strong
• insoluble in water
• high melting point
• non-conductor