Chapter 1: Organic Chemistry and Chemical Bonding

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Chapter 1 Organic Chemistry and Chemical Bonding

• Outline
• 1.1 Introduction 1.7 Hybrid Orbitals
• 1.2 Chemical Bonds 1.8 Sources of Organic
• 1.3 Ionic Bonds Compounds
• 1.4 Covalent Bonds 1.9 Structure of Organic
• 1.5 Coordinate Covalent Compounds
• Bonds
• 1.6 The Shapes of Molecules

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Introduction

• Organic chemistry is the study of compounds that
  contain carbon.
• In general, bonds in organic compounds are
  covalent while bonds in inorganic compounds are
  ionic.
• Table 1.1 Comparison of properties of organic
  and inorganic compounds

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Table 1.1

• Organic Compounds Inorganic Compounds
• Bonding is mostly covalent Bonding is mostly
  ionic
• May be liquids, solids, or gases Mostly high
  melting
• with low melting points solids
• Mostly insoluble in water Often soluble in water
• Solutions do not conduct Water solutions usually
  
• electricity conduct electricity
• Almost all burn Very few flammable

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Introduction (Contd)

• Organic-living organisms
• Inorganic-rocks, minerals, etc.
• Wöhler NH4Cl AgNCO ? NH2CONH2 AgCl
• Modern definition of organic chemistry suggested
  by Kekulé study of the chemistry of living
  organisms is biochemistry.

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Chemical Bonds

• Chemical Bonds are the powerful attractions that
  hold atoms together. The two types of bonds are
  covalent and ionic.
• Ionic bonds are bonds between ions ions are
  particles with an unequal number of protons and
  neutrons, that is they are charged.

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Ionic Bonds

• Atoms can often lose one or more electrons from
  the valence electrons that surround nucleus.
• An atom that loses one or more electrons becomes
  positively charged and is called a cation.
• e.g. K ? e- K Mg ? 2e- Mg2

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Ions (Contd)

• If an atom gains one or more electrons, it
  becomes negatively charged and is referred to as
  an anion.
• e.g. Br e- ? Br- N 3e- ? N3-
• Metals (left side of the periodic table)
  generally form cations, while non-metals (right
  side of the periodic table) generall form anions.

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The Octet Rule

• The cation, K is stable, however, K2, K3, and
  K1- are unstable and therefore do not exist.
  Why?
• Atoms and ions are most stable when they have a
  complete outer shell of electrons (The Octet
  Rule).

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Imperfections in the Octet Rule

• I. Concentrated charges are unstable (e.g. B does
  not form B3, Cl does not form Cl7).
• II. The octet rule cannot be applied to
  transition metal elements because they are too
  far removed from the noble gas structure (Fe can
  form either Fe2 or Fe3).

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Ionic Bonds

• An ionic bond is the attraction between positive
  and negatively charged ions.

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Ionic Bonds (Contd)

• The strength of an ionic bond depends on the
  distance between the centers of the ions.
• Matter we deal with every day is electrically
  neutral nature does not allow a large build up
  of positive or negative charge.

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Covalent Bonds

• A covalent bond is one in which two atoms share
  a pair of electrons.

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Orbitals

• Orbital Picture of Fluorine (draw on board)
• Fluorine has the electron configuration
• 1s22s22px22py22pz1
• The lone electron is found in a 2p orbital. 2 2p
  orbitals overlap to form a covalent bond. This
  is called a molecular orbital because it binds to
  atoms together to form a molecule.

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Orbitals (Contd)

• A covalent bond is called a sigma (?) orbital.
• Each nonmetallic atom has a tendency to form a
  particular number of covalent bonds.
• This number is equal to the number of electrons
  that must be shared to achieve a noble-gas
  electronic configuration.

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Covalent Bonds to Carbon
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Double and Triple Bonds

• The four covalent bonds that carbon needs to make
  to fulfill the octet rule can be 4 sigma bonds or
  a combinations of sigma and pi (double and triple
  bonds).
• The previous illustrations are called structural
  formulas . A structural formula shows all the
  atoms in a molecule and all the bonds connecting
  them.
• A molecular formula gives less information since
  it shows only the number of atoms but not the
  bonds.

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Lewis Structures

• A Lewis Structure shows not only all atoms and
  covalent bonds but also all other outer-shell
  electrons, including unshared.

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Examples of Lewis Dot Structures

• Draw Lewis Dot Structures on the board.

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Rules for Drawing Lewis Dot Structures

• I. Count the number of valence electrons.
• II. Draw a skeleton structure for the species,
  joining atoms by single bonds.
• III. Determine the number of valence electrons
  still available for distribution.
• IV. Determine the number of valence electrons
  required to fill an octet for each atom in the
  skeleton.

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Exceptions to the Octet Rule

• The second row of elements , particularly Sulfur
  and Phosphorous, can hold more than 8 electrons
  in their outer most shell.

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Coordinate Covalent Bonds

• Covalent bonds can form in which one atoms
  supplies both electrons and the other supplies
  none. This type of bond is called a coordinate
  covalent bond.

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Coordinate Covalent Bonds (Contd)

• A coordinate covalent bond has the same
  characteristics as any other covalent bond once
  it is formed.
• Certain metal ions, such as transition metals,
  form many compounds that contain coordinate
  covalent bonds (coordination compounds).

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The Shapes of Molecules

• Molecules have definite 3-D shapes. The geometry
  of a molecule determines the properties,
  including reactivity, of that compound.
• The theory that allows us to predict the shape or
  geometry or shape of molecules is known as VSEPR
  (Valence Shell Electron Pair Repulsion).

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VSEPR

• The theory simply put states that electrons pairs
  in the outer shell of an atom try to get as far
  away from each other as possible.
• Do several examples of various geometries.

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Hybrid Orbitals

• Lewis dot structures and VSEPR provide insight
  into bonding and allow for the prediction of
  molecular geometries, however, there are
  limitations to these concepts.
• I. They do not explain why a double bond is more
  reactive than a single bond.
• II. Why carbon forms 4 equal bonds with 4
  hydrogens in methane.

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Hybrid Orbitals (Contd)

• Do several examples on board.

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Sources of Organic Compounds

• There are currently more than 8 million known
  organic compounds compared to 200,000-300,000
  inorganic compounds.
• What is unique about carbon?
• I. Carbon atoms form stable bonds with other
  carbon atoms, so that both short and long chains
  as well as whole networks can form.

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Sources (Contd)

• II. Carbon can form stable bonds with other
  elements such as N, O, S, H, and the halogens.
• III. Carbon forms 4 bonds which allows for a wide
  variety of combinations.