Chemical Bonding

Chemical Bond The forces that hold groups of atoms together and make them function as a unit Bonding involves only the valence electrons There are 2 types of bonds: Ionic: Transfer of electrons from a metal and to a nonmetal Covalent: Sharing of electrons between 2 nonmetals Note: When 2 metals bond an alloy is formed Electrons are transferred or shared to give each atom a noble gas configuration (stable octet) This is known as the octet rule

Lewis Diagrams Valence electrons involved in bonding can be represented by Lewis dot diagrams A chemical symbol represents the nucleus and the core electrons (not involved in bonding). Dots around the symbol represent valence electrons.

Drawing Lewis Diagrams Cl Write the element symbol. Draw dots, one for each valence electron Dots should be spread over 4 sides It does not matter what side the dots are placed, but do not start to pair dots until there is one on each side The number of valence electrons is equal to the group number. With one exception.

Lewis diagrams for the first 20 elements

Ionic Bonding

Ionic Bonding Metals Nonmetals Electron donors Donate their valence electrons to become a positive ion (cation) Nonmetals Electron acceptors Accept valence electrons to become a negative ion (anion)

Ionic Bonding

Ionic Bonding The two oppositely charged ions are attracted to each other by a force called an ionic bond

Monatomic Cations Name H+ Hydrogen Li+ Lithium Na+ Sodium K+ Potassium Mg2+ Magnesium Ca2+ Calcium Ba2+ Barium Al3+ Aluminum

Monatomic Anions Name F- Fluoride Cl- Chloride Br- Bromide I- Iodide O2- Oxide S2- Sulfide N3- Nitride P3- Phosphide

Properties of Ionic Compounds Structure: Crystalline solids Melting point: Generally high Boiling Point: Electrical Conductivity: Excellent conductors, molten and aqueous Solubility in water: Generally soluble

NaCl Crystal Lattice Ionic compounds form solids at SATP. Ionic compounds organize in a characteristic crystal lattice of alternating positive and negative ions. All lattices are arranged so that each ion has the greatest possible number of oppositely charged ions close by, while keeping similarly charged ions as far away as possible

Representing Ionic Compounds Lewis Diagrams Formation of sodium chloride: Cl · · · ® Na+ [ ] Cl · · Na · +

Lewis Structures for Ionic Compounds Ba • O •• •• O Ba 2+ 2- Ba and O BaO Mg • Cl •• •• Cl Mg 2+ - 2 Mg and Cl Binary ionic compounds. Note the types of arrows used to move electrons – fishhooks for single e-. Write the Lewis symbol for each atom Determine how many e- each atom must gain or lose. Use multiples of one or both ions to balance the number of electrons. MgCl2

Covalent Bonding

Covalent Bonding Electrons are shared between two nonmetals Weaker attractive force than ionic bonding

Properties of Molecular Compounds State at SATP Typically gases & liquids, but some solids Structure Variable (waxy to brittle) Melting & Boiling Points Low Electrical Conductivity Nonelectrolyte Solubility in Water Variable (low to high) Confused?? Don’t worry…more answers to come

Covalent Bonding Formation of hydrogen chloride: Cl ® Cl H H + Lone pairs, valence electrons not involved in covalent bond Formation of hydrogen chloride: · · Cl · · · ® Cl · · H H · + ® H - Cl · · · · Covalent bond, shared electrons Structural Formula: H-Cl (lone pairs are not drawn)

+ Lewis Structures H H2: ® H H or H H Cl + ® Cl Cl Cl2: or Cl Cl · + H2: ® H H or H H Cl · · · + ® Cl Cl · · Cl2: or Cl Cl · · Structural Formula: Cl-Cl

Double and Triple Bonds Atoms can share 4 electrons to form a double bond or 6 electrons to form a triple bond. = O O · · O2: · · N N  N2: E.g. H, C, N, O, F The number of shared electron pairs (covalent bonds) that an atom can form is the bonding capacity.

Multiple Covalent Bonds • • N • •• •• N • • N •• • • N • •• N ••

Multiple Covalent Bonds • • • C O • •• • • O • C • • • O • • • • • • • • C O •• C O ••

Drawing Lewis Structures Arrange the element symbols. Central atoms are generally those with the highest bonding capacity. Carbon atoms are always central atoms Hydrogen atoms are always peripheral atoms Add up the number of valence electrons from all atoms. For polyatomic ions, add one electron for each negative charge and subtract one for each positive charge. Draw a skeleton structure with atoms attached by single bonds. Complete the octets of peripheral atoms. Place extra electrons on the central atom. If the central atom doesn’t have an octet, try forming multiple bonds by moving lone pairs.