CHAPTER Molecular Geometry and Lewis Dot Structures Bonding

2 7.3 Molecular Geometry and Lewis Dot Structures Each water molecule contains one oxygen atom and two hydrogen atoms. One central oxygen atom One hydrogen atom on either side

3 7.3 Molecular Geometry and Lewis Dot Structures Each water molecule contains one oxygen atom and two hydrogen atoms. One central oxygen atom One hydrogen atom on either side Why can’t a water molecule be like this?

4 7.3 Molecular Geometry and Lewis Dot Structures Why can’t a water molecule be like this? The oxygen forms one bond One hydrogen forms two bonds One hydrogen forms one bond The Lewis structures indicate that it is not possible

5 7.3 Molecular Geometry and Lewis Dot Structures Lewis structures for individual atoms are like puzzle pieces. Put them together to form molecules.

6 7.3 Molecular Geometry and Lewis Dot Structures Use Lewis structures to predict: 1) the chemical formula The chemical formula for water is H 2 O (2 hydrogen atoms for every 1 oxygen atom)

7 7.3 Molecular Geometry and Lewis Dot Structures Use Lewis structures to predict: 1) the chemical formula 2) the bonding pattern Oxygen must be the central atom

8 7.3 Molecular Geometry and Lewis Dot Structures Use Lewis structures to predict: 1) the chemical formula 2) the bonding pattern 3) the shape of the molecule H 2 O is flat and bent

9 7.3 Molecular Geometry and Lewis Dot Structures Use Lewis structures to predict: 1) the chemical formula 2) the bonding pattern 3) the shape of the molecule H 2 O is flat and bent To be discussed later in this section

Molecular Geometry and Lewis Dot Structures Consider the chemical formula C 2 H 6 O Does this look right?

Molecular Geometry and Lewis Dot Structures Ethanol Consider the chemical formula C 2 H 6 O

Molecular Geometry and Lewis Dot Structures Consider the chemical formula C 2 H 6 O Could this be right too?

Molecular Geometry and Lewis Dot Structures Consider the chemical formula C 2 H 6 O Dimethyl ether

Molecular Geometry and Lewis Dot Structures isomer: a specific structure of a molecule, only used when a chemical formula could represent more than one molecule. Dimethyl etherEthanol Two isomers of C 2 H 6 O

Molecular Geometry and Lewis Dot Structures Give three isomers for the formula C 3 H 8 O. Show the Lewis dot diagram and the structural formula for each molecule.

Molecular Geometry and Lewis Dot Structures Give three isomers for the formula C 3 H 8 O. Show the Lewis dot diagram and the structural formula for each molecule. Asked:The Lewis dot diagrams and structural formulas for the three molecules represented by the formula C 3 H 8 O Given:Carbon has four unpaired electrons, hydrogen has one, and oxygen has two. Three carbons, eight hydrogens and one oxygen form each molecule. Relationships:The atoms will bond together such that all unpaired electrons will be paired up with electrons from other atoms.

Molecular Geometry and Lewis Dot Structures Give three isomers for the formula C 3 H 8 O. Show the Lewis dot diagram and the structural formula for each molecule. Asked:The Lewis dot diagrams and structural formulas for the three molecules represented by the formula C 3 H 8 O Given:Carbon has four unpaired electrons, hydrogen has one, and oxygen has two. Three carbons, eight hydrogens and one oxygen form each molecule. Relationships:The atoms will bond together such that all unpaired electrons will be paired up with electrons from other atoms. Solve:

Molecular Geometry and Lewis Dot Structures EtheneEthyne Multiple bonds Carbon, nitrogen and oxygen commonly form double and triple bonds. Double bond (2 pairs of electrons) Sharing a pair of electrons is called a single bond. Triple bond (3 pairs of electrons)

Molecular Geometry and Lewis Dot Structures Bond atoms together, forming single bonds. Acetonitrile (C 2 H 3 N)

Molecular Geometry and Lewis Dot Structures Bond atoms together, forming single bonds. Form double bonds by bringing together single electrons from atoms that are already bonded. Acetonitrile (C 2 H 3 N)

Molecular Geometry and Lewis Dot Structures Bond atoms together, forming single bonds. Form double bonds by bringing together single electrons from atoms that are already bonded. Form triple bonds with any remaining single electrons. Acetonitrile (C 2 H 3 N)

Molecular Geometry and Lewis Dot Structures Bond atoms together, forming single bonds. Form double bonds by bringing together single electrons from atoms that are already bonded. Form triple bonds with any remaining single electrons. Write final Lewis dot structure and structural formula. Acetonitrile (C 2 H 3 N)

Molecular Geometry and Lewis Dot Structures Bond atoms together, forming single bonds. Formaldehyde (CH 2 O)

Molecular Geometry and Lewis Dot Structures Bond atoms together, forming single bonds. Form double bonds by bringing together single electrons from atoms that are already bonded. Formaldehyde (CH 2 O)

Molecular Geometry and Lewis Dot Structures Bond atoms together, forming single bonds. Form double bonds by bringing together single electrons from atoms that are already bonded. Form triple bonds with any remaining single electrons. Write final Lewis dot structure and structural formula. Formaldehyde (CH 2 O)

Molecular Geometry and Lewis Dot Structures Use Lewis structures to predict: 1) the chemical formula 2) the bonding pattern 3) the shape of the molecule H 2 O is flat and bent To be discussed later in this section

Molecular Geometry and Lewis Dot Structures The lone pairs of electrons are not involved in bonding, but affect the shape of the molecule. V alence S hell E lectron P air R epulsion H 2 O is flat and bent

Molecular Geometry and Lewis Dot Structures V alence S hell E lectron P air R epulsion H 2 O is flat and bent VSEPR: a theory that states that the shapes of molecules are dictated, in part, by the repulsion of the shared electrons and the unshared pairs of electrons.

Molecular Geometry and Lewis Dot Structures Similar charges repel each other. Identify regions of electron density to predict the molecular geometry. Carbon dioxide 2 REGIONS

Molecular Geometry and Lewis Dot Structures Similar charges repel each other. Identify regions of electron density to predict the molecular geometry. Carbon dioxide 2 REGIONS Formaldehyde 3 REGIONS

Molecular Geometry and Lewis Dot Structures Similar charges repel each other. Identify regions of electron density to predict the molecular geometry. Carbon dioxide FormaldehydeMethane 2 REGIONS3 REGIONS4 REGIONS

Molecular Geometry and Lewis Dot Structures Two regions Two charged balloons repel in opposite directions Two areas of electron density repel to form linear shapes

Molecular Geometry and Lewis Dot Structures Two regions Two charged balloons repel in opposite directions Two areas of electron density repel to form linear shapes These two regions of electron density repel each other, forming a 180 o angle

Molecular Geometry and Lewis Dot Structures Two regions Two charged balloons repel in opposite directions Two areas of electron density repel to form linear shapes These two regions of electron density repel each other, forming a 180 o angle

Molecular Geometry and Lewis Dot Structures Two areas of electron density repel to form linear shapes The two 180 o angles formed around each carbon make the entire molecule straight. Two regions

Molecular Geometry and Lewis Dot Structures Two regions There are two isomers for the formula C 3 H 4. Show the Lewis dot diagram for each molecule, and indicate which atoms are at the center of a linear part of the molecules.

Molecular Geometry and Lewis Dot Structures Two regions There are two isomers for the formula C 3 H 4. Show the Lewis dot diagram for each molecule, and indicate which atoms are at the center of a linear part of the molecules. Asked:The linear parts of each isomer of C 3 H 4 Given:There are two different isomers. Part of each molecule will be linear. The molecules are made from three carbons and four hydrogens. Relationships:Each atom that has two regions of electron density around it will form a linear part of the molecule.

Molecular Geometry and Lewis Dot Structures Two regions There are two isomers for the formula C 3 H 4. Show the Lewis dot diagram for each molecule, and indicate which atoms are at the center of a linear part of the molecules. Asked:The linear parts of each isomer of C 3 H 4 Given:There are two different isomers. Part of each molecule will be linear. The molecules are made from three carbons and four hydrogens. Relationships:Each atom that has two regions of electron density around it will form a linear part of the molecule. Solve:

Molecular Geometry and Lewis Dot Structures Three regions Three charged balloons repel into the corners of a triangle Three areas of electron density repel to form trigonal planar shapes

Molecular Geometry and Lewis Dot Structures Three regions Three charged balloons repel into the corners of a triangle Three areas of electron density repel to form trigonal planar shapes These three regions of electron density repel, forming 120 o angles between the three atoms bonded to each carbon atom

Molecular Geometry and Lewis Dot Structures Three regions Three charged balloons repel into the corners of a triangle Three areas of electron density repel to form trigonal planar shapes These three regions of electron density repel, forming 120 o angles between the three atoms bonded to each carbon atom

Molecular Geometry and Lewis Dot Structures Three areas of electron density repel to form trigonal planar shapes Three regions These three regions of electron density repel, forming 120 o angles between the three atoms bonded to each carbon atom

Molecular Geometry and Lewis Dot Structures Acetic acid when mixed with water is commonly known as vinegar and has the formula C 2 H 4 O 2. The correct isomer has both oxygens bonded to the same carbon. Draw the Lewis dot structure for this isomer and indicate where the molecule will be trigonal planar. Three regions

Molecular Geometry and Lewis Dot Structures Acetic acid when mixed with water is commonly known as vinegar and has the formula C 2 H 4 O 2. The correct isomer has both oxygens bonded to the same carbon. Draw the Lewis dot structure for this isomer and indicate where the molecule will be trigonal planar. Three regions Asked:The trigonal planar parts of acetic acid Given:The formula for acetic acid is C 3 H 4 O 2 and both oxygens are bonded to the same carbon. Relationships:Each atom that has three regions of electron density around it will form a trigonal planar part of the molecule.

Molecular Geometry and Lewis Dot Structures Acetic acid when mixed with water is commonly known as vinegar and has the formula C 2 H 4 O 2. The correct isomer has both oxygens bonded to the same carbon. Draw the Lewis dot structure for this isomer and indicate where the molecule will be trigonal planar. Three regions Asked:The trigonal planar parts of acetic acid Given:The formula for acetic acid is C 3 H 4 O 2 and both oxygens are bonded to the same carbon. Relationships:Each atom that has three regions of electron density around it will form a trigonal planar part of the molecule. Solve:

Molecular Geometry and Lewis Dot Structures Four regions Four charged balloon repel into the corners of a tetrahedron, rather than lying flat in a plane The four regions of electron density around the carbon repel, forming angles of o.

Molecular Geometry and Lewis Dot Structures Four regions The four regions of electron density around the carbon repel, forming angles of o.

Molecular Geometry and Lewis Dot Structures Four regions Ammonia (NH 3 ) forms a trigonal pyramidal shape Lone pair of electrons The lone pair of electrons repels the shared electrons in the H–N bonds, pushing the hydrogens away from the lone pair Lone pairs of electrons repel just like shared pairs

Molecular Geometry and Lewis Dot Structures Four regions Different geometries formed by atoms with four regions of electron density Trigonal pyramidal Tetrahedral Bent

Molecular Geometry and Lewis Dot Structures What shapes are formed within the isomer of C 4 H 5 NO, which has a triple bond connecting nitrogen?

Molecular Geometry and Lewis Dot Structures Four regions What shapes are formed within the isomer of C 4 H 5 NO, which has a triple bond connecting nitrogen? Solve:

Molecular Geometry and Lewis Dot Structures Use Lewis structures to predict: 1) the chemical formula 2) the bonding pattern 3) the shape of the molecule