Bonding

1
Bonding

• Controls hardness, cleavage, conductivity etc.

2
Types of bonds

• Those that
• Involve valence electrons
• Those that dont
• Valence bonds
• Never with nobel gases since the valence shell is
  full
• Other elements want to be like nobel gases

3
Ionic bonds

• TRANSFER of electrons so both elements have nobel
  gas configuration
• i.e. NaCl

4
characteristics

• Very symmetric structure (NaCl)
• Strong bonds
• High melting T
• Brittle
• Soluable
• Poor conductors

5

• How does ion charge affect bond strength?
• How does bond length affect bond strength?
• How does bond length determine hardness?

6
Covalent bonds (the socialist bond)

• Sharing of electrons between two atoms
• Consider 2 Cl atoms each trying to steal each
  other's e- 1s2 2s2 2 p6 3s2 3p5
• Can't do, but if draw close until overlap an
  outer orbital, perhaps can share whereby 2 e-
  "fill" the remaining 3p shell of each Cl
• Actually fill it only 1/2 the time for each, but
  better than nothing
• Double bonds when 2 orbitals shared
• Triple bonds when 3 orbitals shared

7
Carbon Lewis dot structure
8
Covalent bond properties

• Insoluable
• Very high melting T
• Very stable
• Non-conductor (no e- readily available)

9
Metallic bonds (free electron love)

• Metal nuclei are positively charged spheres with
  valence electrons forming a mobile glue
• Type of covalent bond but between like atoms and
  electrons are free to move from atom to atom
• Difference electronegativity

10
Electronegativity

• How easily an element gains or looses valence
  electrons

11
Low electronegativity looses electrons easily
12
Metallic bonds

• Also occurs if you need large s of electrons to
  get noble gas configuration
• Na needs how many e-?

13
Metallic bonds

• Not sharing between specific orbitals but sea of
  mobile electrons
• Characteristics
• Soft and malleable
• High conductivity

14
Predicting bond types

• Bonds between columns 1 and 7 and 2 and 6 are?
• Bonds between like elements are?

15
(No Transcript)
16
Non-valence electron bonds

• Weak electrostatic forces
• Types
• Van der waals
• hydrogen

17
Hydrogen bonds

• In H2O
• Weak polarity of by H atoms and - by O atoms
• Weak attraction between molecules

18
Van der Waals force

• Weakest bond
• Usually between neutral molecules (even large
  ones like graphite sheets)
• Ties neutral structures and molecules into a
  cohesive structure

19

• Over time, charges are neutral but at any one
  time more electrons are on one side than the
  other.
• Net positive charge attracts electrons from
  neighboring sheet

20
Graphite bonding
21
Properites of van der Waals

• Weak bonds
• Soft and greasy feeling
• Talc, graphite, clay minerals, micas, kaolinite
• Low hardness
• Low melting T
• Easy cleavage

22
Atomic and ionic radii

• Can't absolutely determine e- cloud is nebulous
  based on probability of encountering an e-
• In crystalline solids the center-to-center
  distance bond length is accepted to sum of
  ionic radii
• How get ionic radius of X Y in XY compound??

23
Atomic and ionic radii

• Need one pure element first
• Native Cu. Atomic radius 1/2 bond length

Ionic radius
24
Atomic and ionic radii

• With anions and cations of different size
  compare and estimate

25
Atomic radii trends

• In columns, higher atomic , larger radius

26
Atomic radii trends

• In rows, radii decreases as atomic up.

27
Atomic radii trends

• What happens to radius as charge (oxidation
  state)?
• Fe2 or Fe3?

28
Atomic radii trends

• What happens to radius as an atom touches more
  and more other atoms
• Coordination number
• Higher coordination number, larger radious