1. Introduction to Bonding
Key Terms:
Chemical Bond
Ionic Bond
Covalent Bond
Electronegativity
Metallic Bond

2. Why Form Bonds?
Single atoms are not how most of the elements in nature exist
Atoms “seek” the lowest energy state possible
In the dissociated stated, aka individual atom state, most atoms are at a higher energy
When the atoms combine it lowers the total energy of the system, which means it is more favorable

3. Chemical Bonds
A chemical bond forms when 2 or more atoms rearrange valence electrons to increase stability
Remember the term valence electron, what was considered a “magic number” of valence electrons?
Most atoms prefer 8 valence electrons to fill their s- and p- orbitals
Two ways for atoms to share electrons:
Completely transfer
Share the electron(s)

4. Octet Rule
A chemical rule of thumb in which atoms that combine seek to have 8 electrons as their valence electrons
An atom that is surrounded by 8 electrons that only contain s- and p-orbitals as valence orbitals will be stable

5. Ionic Bonding
Ionic bonding forms when valence electrons are transferred from one atom to another
When an ionic bond is present the compound is considered an ionic compound
One of the most common examples of an ionic compound is that of common table salt, NaCl

6. Ionic Bonding

7. Anions and Cations Ionic compounds are comprised of: Cations- Anions-
An atom or molecule that loses an electron to become positively charged
Anions-
An atom or molecule that gains an electron to become negatively charged

8. Properties of Ionic Compounds
Ionic Compounds are arranged in crystal lattice structures to put the atoms in the lowest energy state possible
Strong forces hold the ions together
High melting and boiling points
Hard- not easily crushed
Conduct electricity when melted or dissolved because ions are free to move

9. Pure Water vs Salt Water
If you are sitting in a pool of pure water and someone drops a plugged in toaster in with you. What will happen to you?
Nothing
Now, if someone adds salt to the pool before you get in what would happen once the plugged in toaster is added?
Zap!

10. Covalent Bond
A covalent bond occurs when electrons are shared when forming molecules
Formation of molecules causes increased stability
Covalent compound have weaker forces holding them together compared to that of ionic bonds

11. Properties of Covalent Bonds
Covalent compounds have:
Lower melting and boiling points
Many covalent compounds are volatile liquids or gases
Soft- easier to crush
Are not conductors of electricity
Ex.
Methane is a covalently bound molecule that is a gas or a volatile liquid

12. Electronegativity
Electronegativity is a property that tells how strong an atom’s attraction is for electrons
Electronegativity is a property of an atom that can be found using a chart or table
What do you think happens when one atom has a stronger pull on an electron than another?
Think of a large dog and a smaller dog playing tug of war
Unequal sharing

13. Polar Covalent Bonds
Polar covalent bonds occur when electrons are shared unequally giving these molecules charged ends or poles
Since oxygen has a higher electronegativity than hydrogen, oxygen holds onto shared electrons more, giving the oxygen a partial negative charge and the hydrogen a partial positive charge
This type of unequal sharing is denoted by a ∂+ or ∂- to say slightly more positive or negative at that atom

14. Nonpolar Covalent Bonds
Nonpolar covalent bonds occur when electrons are shared equally because the atoms have the same or close electronegativities
Nonpolar compounds tend to have weaker interactions between molecules while polar compounds have stronger interaction between molecules
This idea of molecules interacting with each other will be covered in a later lesson

15. Determining Bond Type Electronegativity Difference Type of Bond
Greater than or equal to 1.7
Ionic bond
Between 1.7 and 0.3
Polar Covalent
Less than or equal to 0.3
Nonpolar covalent

16. Metallic Bond
Metallic Bonds form in metals because the electrons are delocalized, giving metals a “sea of electrons”
Due to this “sea” metals have the following properties
Luster
Conductors
Malleable
Ductile

17. Practice Problems
Determine the type of bonds for the following compounds:
Mg and F
4.0 – 1.2 = ionic
S and O
3.5 – 2.5 = polar covalent
Na and Cl
3.0 – 0.9 = 2.1 ionic
N and O
3.5 – 3.0 = 0.5 (slightly) polar covalent
B and F
4.0 – 2.0 = 2.0 ionic