1. Chemical Bonding
Mr. Tsigaridis

2. Chemical Bonding
Of all the elements in the universe, that either occur naturally or synthetically, only the elements known as the Nobel gases exist as uncombined atoms
The rest of the elements in the universe are held together by chemical bonds in molecules or compounds
These bonds exists because of a difference in electrostatic forces in the molecules

3. Chemical Bonding
If you recall from your previous classes, the electrostatic forces are created when electrons move from one atom to another and by doing so, change the charges associated to those atoms
This is a process known as Ionization, where some atoms become cations, and others become anions

4. Chemical Bonding The reason that bonding occurs is becasue of energy
We saw that when you take an object and give it some energy (ex. holding an apple in the air), and then allowing the apple to do as it will, it reconfigures itself in the most energy efficient way
In nature, lower energy systems are favoured over higher energy systems (they are more favourable)

5. Chemical Bonding
We have also seen this characteristic dropping in overall energy in the electrons within atoms (lowest electron configuration)
There are even shapes that are more energy efficient
Think about the shape of every planet in the universe, or indeed the shapes of the very building blocks of everything, the atoms, they are all relatively spherical because a sphere is the most energy efficient shape

6. Lewis Structures
Later in this course we will be using Lewis structures to determine the 3D conformational shape of specific molecules and compounds, but for now we will use them in an attempt to explain chemical bonding
Lewis structures, as many of you already know express pictorially what the valence shell (outer shell) of an atoms is like in terms of its electrons and their configuration

7. Lewis Structures
The reason that we want to represent the valence shell is that the valence electrons are the only ones that take place in chemical bonding
They can either be shared between atoms or they can be donated completely
When we represent Lewis structures in this course we will represent them using dots to represent the lone pairs of electrons and lines between atoms to represent bonding pairs of electrons

8. Lewis Structures

9. Lewis Structures

10. Ionic Bonding
When an ionic bond occurs, it is the attraction between oppositely charged atoms (cations and anions) that constitute an ionic bond
This occurs between elements with large differences in electronegativity
Usually a metal with a low electronegativity and a non-metal with a high electronegativity
These compounds are usually arranged in an crystalline structure much like an array which makes them form crystals

11. Ionic Bonding
As you can see from the diagram below, salt crystals are formed when you have an alternating atoms of chlorine and sodium
This alternating pattern makes the ionic bonds very strong and difficult to break apart from simply heating

12. Ionic Bonds
If we take another compound, using Lewis structures we can see how bonds start to form

13. Ionic Bonds
Similarly, if we use the electron configurations we see that after the bonding occurs, there is a reconfiguration of the electrons into the most energy favourable state
Sodium
Fluoride 3s 2s 2p 1s

14. Properties of Ionic Solids
Ionic Solids have the following properties
Crystals with smooth shiny surfaces
Hard
Brittle
Non-conductors of electricity and heat
High melting points

15. Covalent Bonding
The word covalent when broken down means to share the valence shell or valence electrons
Atoms will do this with other atoms in order to achieve noble gas electron configuration
When a bond is made, a pair of electrons fills the valence level for both atoms
The areas where there is overlap represent areas of increased electron density
Increased Electron Density

16. Covalent Bonding
Covalent bonding involves a delicate balance of attractive and repulsive forces between electrons and the nuclei of atoms
Electrons and electrons naturally repel one another and similarly two nuclei
Electrons and the nucleus, have an attractive force between them due to the opposite charges they posses

17. Covalent Bonds
When you have studied covalent bonding, and ionic bonding for that fact, you have learned that they must follow a rule called the octet rule (noble gas configuration) and bonding at the 2p level must still obey this rule

18. Covalent Bonding
The previous example of fluorine gas shows that covalent bonds form single bonds within molecules, but they may also form double and triple bonds as well
Single Bond
Double Bond
Triple Bond