Lewis Structures - Chapter 3 Molecular Shape and Structure...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 3 Molecular Shape and Structure The VSEPR Model (Sections 3.1–3.3) Key Concepts molecular formula, structural formula, space-filling model, ball-and-stick model, bond angle, valence-shell electron-pair repulsion (VSEPR) model, bonding pairs, lone pairs, central atom, electron arrangement about central atom, multiple versus single bonds, polar bond, nonpolar bond, polar molecule, nonpolar molecule; molecular shapes: linear, angular (bent), trigonal planar, trigonal pyramidal, tetrahedral, square pyramidal, trigonal bipyramidal, octahedral, T-shaped, seesaw, square pyramidal, square planar Representation of Molecules Molecular formula Number and types of atoms present in the molecule or ion Structural formula Atoms represented by chemical symbols, linked by lines Lewis structure Atoms represented by chemical symbols, valence electrons shown as lines ( bonds ) or dots ( lone pairs ) Space-filling model Shaded or colored shapes (atoms) that fit into one another Ball-and-stick model Shaded or colored balls (atoms) linked by sticks (bonds) Examples for Ammonia Type Example Advantage(s) Disadvantage(s) Molecular formula NH 3 Shows chemical omposition c No structural information Structural formula N H H H Shows chemical connectivity (which atoms re bonded together) a Little three-dimensional structural information Lewis structure N H H H Shows chemical connectivity and all valence electrons involved in onding, reactivity b Little three-dimensional structural information Space-filling model Three-dimensional contour of molecule clearly visible Bonds difficult to see, particularly for interior atoms Ball-and-stick model Atoms, connectivity, and eneral shape visible g Poor representation of actual bonds and atoms 1
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Chapter 3 3.1 The Basic VSEPR (Valence-Shell Electron-Pair Repulsion) Model Example 3.1a Use the VSEPR model to predict the shape of (1) fluoromethane, CH 3 F ; (2) the phosphate anion, PO 3 3 ; (3) sulfur hexafluoride, SF 6 ; and (4) tetrafluoroethene (tetrafluorethylene), C 2 F 4 . All are molecules with no lone pairs ( m = 0). Solution For each molecule, follow the general procedure outlined above. Answer (1) The Lewis structure of CH 3 F (C is the central atom) is C H H F H The molecule has 14 valence electrons. There are four bonding electron pairs around carbon. The shape is tetrahedral . The bond angles will not be exactly 109.5 ° because the terminal atoms are not all identical. The molecule CH 3 F is an AX 4 species. The lone pairs on the fluorine atom are not considered because it is a terminal atom. (2) One Lewis structure of PO 4 3 is PO O O O 3 The molecule has 32 valence electrons. Because the multiple bond is counted as one electron pair (a single unit of high electron density), there are then four bonding electron pairs around phosphorus. The shape is again tetrahedral . The terminal atoms are identical. The bond angles are exactly 109.5 ° . The anion PO 4 3 is an AX 4 species. The Lewis structure is an example of octet expansion on the central P atom. An equally acceptable Lewis structure with four single bonds between P and O gives the same answer.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 05/30/2008 for the course CHEM 2070 taught by Professor Chirik,p during the Fall '05 term at Cornell University (Engineering School).

Page1 / 11

Lewis Structures - Chapter 3 Molecular Shape and Structure...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online