Joule Centre courses in Power System Protection

Ellis Cbu

Description

• cours - matière potentielle : speakers
• cours - matière potentielle : content
• cours - matière potentielle : modules

North West Higher Level Skills Partnership Joule Centre courses in Power System Protection

• electrical power systems
• protection relays
• centre eligibility criteria
• substation communication standards for power system automation
• circuit faults
• distribution networks
• power system protection
• protection
• control
• course

Sujets

• Content
• Module
• Crossley
• University of Manchester
• Siemens
• National Grid
• Protection
• Course
• Fault

Informations

• Publié par: thaut
• Nombre de lectures: 18
• Langue: English

Extrait

Lecture 19

CHE 131 Lecture 19, 3/5/2007

Working with Molecular Models(9.1) Predicting Molecular Shapes: VSEPR(9.2)

Benjamin S. Hsiao Department of Chemistry Stony Brook University

Molecular Models

The Water Molecule

1

Lecture 19, Knowledge and Skills

 Be aware of some of the limitations of molecular models  Predict the structures of simple molecules using the VSEPR model  Know the basic geometries of the arrangement of electron pairs about central atoms  Estimate the relative spatial demands of different types of electron pairs lone pairs, bonding pairs, single bonds, multiple bonds, bonds involving elements of different electronegativity

Fig. 918, p.410

CHE 131 Lecture 19, 3/5/2007

Perspective Structure

Fig. 92, p.385

2

Determine and represent the structure of a (simple) molecule

Molecular structure

(trigonal pyramidal)

p.394a

Model of molecular structure

p.390a

CHE 131 Lecture 19, 3/5/2007

VSEPR, Valence Shell Electron Pair Repulsion

Electrons in molecules are organized in pairs. Types of electron pairs: Bonding electron pairs (BP) Single or combined into multiple bonds Lone electron pairs (LP)

Electron pairs repel each other. They move away from each other as far as possible. The electron pairs emanating from a central atom point towards the corners of regular geometric shapes. The regular geometric shapes may have to be modified in order to account for the relative magnitudes of repulsion between different types of electron pairs.

Balloon VSEPR Models

3

1.

2.

3.

Number of electron pairs 2

3

4

5

6

Geometric arrangement

linear

trigonal

tetrahedral

trigonal bipyramidal (square pyramidal)

octahedral

VSEPR Basic Geometries

VSEPR Procedure and Rules

Write the Lewis structure of a molecule.

.

.

Count the number of electron pairs. Bundle the electron pairs of multiple bonds into one group. Determine the basic geometry.

Refine the basic geometry. Identify the preferred sites for the more strongly repelling electron pairs and adjust angles.

Relative magnitudes of repulsions: LPLP > LPBP > BPBP triple bond > double bond > single bond

Preferred sites for the more strongly repelling electron pairs: Linear, trigonal, and tetrahedral: All sites are equivalent. Trigonal bipyramidal: Equatorial sites Octahedral: All first sites are equivalent. Preferred second site is opposite to first site.

CHE 131 Lecture 19, 3/5/2007

Relative magnitudes of repulsions Illustrative Example: Conversion of lone pair to bonding pair

B B

. .

A

B

add proton

B B

H . .

A

Three and Four Electron Pairs

B

Distinction between electronpair geometry and molecular geometry!

+

4

Idealized VSEPR Geometries

Five and Six Electron Pairs

1. Lewis Structure: on P atom: 5 bond pairs 0 lone pair→

2. Basic geometry: trigonal bipyramidal

AX 5

3. Refined geometry: No refinement required.

4. Molecular structure: Identical with VSEPR structure.

1. Lewis Structure:

on I atom: 4 bond pairs 2 lone pairs→

Cl

F

AX E 4 2

3. Refined geometry: arrangement of lone pairs correct

PCl 5 Cl Cl P Cl l

 [IF ] 4

F .. .. I F

F

Cl

Cl

Cl

P

l

CHE 131 Lecture 19, 3/5/2007

Cl

2. Basic geometry: octahedral . . F F I F F . .

4. Molecular structure: F F I F F

square planar

5

Molecule of the Week: Iodine Heptafluoride, IF 7 F F F 1. Lewis Structure: F I F on I atom: F F 7 bond pairs F 0 lone pair→AX 7 F F 2. Basic geometry: I pentagonal bipyramidal F F The geometry of this molecule is indeed pentagonal F bipyramidal, but the congestion of the five equatorial fluorine atoms is so severe that they move in and out of that plane readily. So the molecule changes shape very rapidly. This molecule exhibits “fluxional” structural behavior. J. Am. Chem. Soc.1993,115, 1520.

Refinement of the Basic VSEPR Geometry Influence of electron lone pairs

F

p.390b

4. Molecular structure:

on S atom: 3 bond pairs 2 lone pair

→

2. Basic geometry:

 [SF ] 3

CHE 131 Lecture 19, 3/5/2007

2. Basic geometry:

1. Lewis Structure: on N atom: 3 bond pairs (between double and single, all equal) 0 lone pair→AX 3 . . . . : O : : O : : O : + + + . . . . . . . . N N N : : O O : : O O : : O O . . . . . . . . . . . .

F

.. .. S

F

IF 5 F 1. Lewis Structure: .. F F I on I atom: F F 5 bond pairs 1 lone pair→AX E 5

3. Refined geometry:

4. Molecular structure:

3. Refined geometry:

6

SOCl 2 .. 1. Lewis Structure: Cl S Cl on S atom: 3 bond pairs (1 double, 2 single) 1 lone pair→AX YE 2

with resonance: 3 equivalent bond pairs

1. Lewis Structure:

F

AX E 3 2

3. Refined geometry:

4. Molecular structure:

 Nitrate, NO 3

2. Basic geometry:

2. Basic geometry:

4. Molecular structure:

3. Refined geometry:

ICl F 2 2 F 1. Lewis Structure: .. F I on I atom: Cl 4 bond pairs l to 2 different elements 1 lone pair→AX Y E 2 2

3. Refined geometry:

CHE 131 Lecture 19, 3/5/2007

2. Basic geometry:

4. Molecular structure:

7

p.398b