Chemical Bonding

1
Chemical Bonding

• An Introduction

2
Chemical Bonds

• A mutual electrical attraction between the nuclei
  and valence electrons of different atoms that
  bonds the atoms together to
• Lower potential energy
• Increase stability

3
Octet Rule

• Atoms will gain, lose or share electrons to have
  eight valence electrons
• A full outer shell means the outermost s and p
  sublevels are full

4
Types of Bonds

• Three general types of bonds
• Ionic
• Covalent
• Metallic
• Type of bond is determined using the
  electronegativities of the atoms involved
• Most compounds have bonds that are partially
  ionic and partially covalent

5
Ionic Bonds

• Electrostatic attraction between ions with
  opposite electrical charges
• No molecules are formed huge numbers of cations
  are bonded to huge numbers of anions
• Formulas are written as the lowest whole number
  ratio of ions

6
Covalent Bonds

• Two atoms share two or more electrons
• Two electrons (1 pair) single bond
• Four electrons (2 pairs) double bond
• Six electrons (3 pairs) triple bond
• The electrons may not be shared evenly, which
  would result in a polar covalent bond

7
Metallic Bonds

• Metals have delocalized electrons, which means
  the electrons are free to move around
• Metallic bonds are the attraction between metal
  atoms and the surrounding sea of electrons
• Metallic bonds are formed when you have only
  metallic elements present

8
Electronegativity

• Tendency of an atom to attract electrons to
  itself
• Values are on your formula chart
• Fluorine is the highest
• Francium is the lowest
• Use the difference in electronegativity to
  classify the bond by type

9
Polar Covalent Bonds

• Some atoms dont share the electrons evenly
• Polar bonds are formed when one atom hogs the
  electrons more than the other
• Non-polar electrons are shared evenly
• Mildly polar electrons are pulled slightly to
  one side
• Very polar electrons are pulled a lot to one side

10
Determining Bond Type

• Find the difference in electronegativity and
  match it to the values shown below

Electronegativity Difference Type of Bond
0.0 0.3 Non-polar covalent
0.3 1.7 Polar covalent
1.7 or more Ionic
11
Determining Bond Type - Example

• What type of bond will be formed between aluminum
  and phosphorus?
• Electronegativity of aluminum 1.5
• Electronegativity of phosphorus 2.1
• Difference 2.1 1.5 0.6
• Mildly polar covalent bond will be formed

12
Wrap-Up 1

• Predict the bond type that will form between the
  following elements
• Oxygen and boron
• 3.5-1.52.0 Ionic
• Lithium and silicon
• 1.8-1.00.8 mildly covalent
• Platinum and gold
• Two metals metallic
• Fluorine and carbon
• 4.0-2.51.5 very polar covalent
• Hydrogen and boron
• 2.1-2.00.1 non-polar covalent

13
Properties of Compounds

• Most properties are determined by the kind of
  bond holding the atoms together
• We can generalize properties using the type of
  bond

14
Properties of Ionic Bonds

• Very strong bond, which leads to
• Crystalline solid at room temperature
• Brittle rather than malleable
• High boiling point
• The ions are locked in place when a solid, so the
  ionic compounds dont conduct electricity or heat
• The ions separate when dissolved in water, so
  solutions of ionic compounds are good conductors

15
Properties of Covalent Bonds

• Weak forces holding the molecules together
  (intermolecular forces), which leads to
• Soft solids, liquids or gases at room temperature
• Low boiling points
• Non-conductive (no ions and the electrons are
  locked into place)

16
Properties of Metallic Bonds

• Sea of electrons leads to
• Good conductivity of electricity
• Good conductivity of heat
• Malleable and ductile
• Shininess

17
Wrap-Up 2

• A new compound has been discovered that is a
  brittle solid at room temperature. It is further
  found to allow a current to pass through a sample
  when it is dissolved into water. What are the
  most likely kind of bonds in this compound?
• Ionic bond

18
Intermolecular Forces

• Hydrogen bonds attraction between hydrogen
  atoms and the negative side of very polar bonds
  (form in water)
• Dipole-dipole forces attractive forces between
  the partial charges on polar molecules
• London dispersion forces (aka van der Waals
  forces) forces created by the motion of
  electrons making temporary polar molecules

19
Ionic bonding Copy This

• metal atom transfers electrons to nonmetal atom
• They do to get stable octets of 8 valence
  electrons on outside
• The metal loses electrons to form positive ion
• The nonmetal gains these electrons and becomes a
  negative ion
• The newly formed positive and negative ions
  attract each other to form the ionic bond

20

• Covalent bonding
• Non-metal atoms share electrons with non-metal
  atoms
• Non-metals dont lose electrons easily they are
  gainers
• They share electrons to form balanced valence
  energy levels
• Metallic bonding
• Metal atoms form a sea of moving electrons
• Metals give up electrons easily
• Electrons move from atom to atom
• Moving electrons form a common electron cloud