Bonding

Introduction to Bonding: Chemical bond: the force that holds two atoms together Bonds may be formed by the attraction of a cation to an anion Bonds may be formed by the attraction of a cation to an anion ionic bond Bonds may be formed by sharing electrons Bonds may be formed by sharing electrons covalent bond

Significance of Bonding Formation of bonds (or breaking bonds) is a chemical change. Formation of bonds (or breaking bonds) is a type of reactivity.

Octet Rule Octet Rule: atoms will gain, lose, or share electrons in order to acquire the stable electron configuration of a noble gas. Try to have 8 electrons around each atom Li + F Li F : : : :: : : This is an example of an ionic compound

Octet Rule Since C only has 4 valence electrons, it can form more than one bond: Note that C achieves an octet of electrons This is an example of a covalent compound

Learning Check Draw the Lewis dot structure for H 2 Draw the Lewis dot structure for H 2 Draw the Lewis dot structure for F 2 Draw the Lewis dot structure for F 2 Draw the Lewis dot structure for a water molecule, H 2 O Draw the Lewis dot structure for a water molecule, H 2 O

Practice Work with your partner to draw the following compounds: NF 3 CCl 4 NF 3 H 2 S SiH 4 CO SiH 4 O 2 CO SO 2 CO 2 SO 2 NO 2

Ionic versus Covalent Bonding

Ionic: electrical force of attraction between a cation and anion; the anion donates both electrons for the bond cation anion

Each cation in the solid ionic compound is surrounded by anions, and each anion is surrounded by cations. Solid ionic compounds form a crystal lattice. Na Cl

Endlessly repeating Lattice of Ions All ionic compounds form, in which the positive and negative ions alternate. All ionic compounds form crystal lattices, in which the positive and negative ions alternate. stress If the ion layers shift slightly ions with the same charge are brought side-by-side causing If the ion layers shift slightly ions with the same charge are brought side-by-side causing repulsion.

Ionic compounds have This is due to the strong attraction of the oppositely charged ions. It takes a lot of heat energy to overcome these Ionic compounds have high melting and boiling points. This is due to the strong attraction of the oppositely charged ions. It takes a lot of heat energy to overcome these strong attractions. Attractions are strongest for smaller ions or ions with greater charge (Mg 2+ O 2- vs. Na + Cl - ). These ionic compounds will have the highest melting and boiling points.

Characteristics of ionic compounds: (usually solid at room temp)  High melting points and boiling points (usually solid at room temp)  Very hard and crystal-like;  Very hard and crystal-like; interactions between molecules are strong (requires atoms to have very different electronegativity)  Occurs between metals and nonmetals (requires atoms to have very different electronegativity)  High polarity  Conduct electricity when melted  Typically dissolve in water

Formation of Ionic Compounds Reacting Compound Example GroupsGeneral Formula Simple Binary Ionic Compounds Table

Covalent: sharing electrons to form a bond; each atom contributes an electron to the bond C O C + O

Representing Covalent Bonds Covalent bonds are shown by a line, representing the shared pair of electrons C H H H H

Multiple Bonds Covalent compounds sometimes form multiple bonds between 2 atoms: a a double bond: O O a a triple bond: N N

Multiple Bonds Double bonds are shorter and stronger than single bonds Triple bonds are shorter and stronger than double bonds It takes more energy to break a double or triple bond

Characteristics of covalent compounds: (usually liquid or gas at room temp)  Low melting points and boiling points (usually liquid or gas at room temp)  Relatively soft and even flexible;  Relatively soft and even flexible; interactions between molecules are weak, allowing the molecules to move (requires atoms to have similar electronegativity)  Occurs between 2 nonmetals (requires atoms to have similar electronegativity)  Nonpolar or low polarity  Poor conductors of electricity but dissolve in nonpolar liquids  Often do not dissolve in water, but dissolve in nonpolar liquids

Ionic, Covalent, or Ionic, Covalent, or Polar Covalent  Ionic bonds form between metals and nonmetals with large differences in electronegativity  Covalent bonds form between nonmetals with smaller differences in electronegativity  Some covalent bonds are The bonding atoms have different electronegativity, causing one atom to pull the shared electrons towards it.  Some covalent bonds are polar. The bonding atoms have different electronegativity, causing one atom to pull the shared electrons towards it.

Polar Covalent Bonds Polar covalent bonds Polar covalent bonds share electrons unequally

Polarity of Bonds

Comparison of ionic solid and covalently bonded solid Na Cl Ionic solid: strong electrostatic interactions Molecular solid: weak intermolecular forces Covalent bonds CH 4

Summary