1. IONS

2. Objectives
Determine the number of valence electrons in an atom of a representative element
Explain how the octet rule applies to atoms of metallic and nonmetallic elements
Describe how cations form
Explain how anions form

3. Key Vocabulary
Octet rule
Ion
Cations
Anions
Halide ions

4. Octet Rule
In 1916, chemist Gilbert Lewis used the fact that noble gases are unreactive in chemical reactions to explain why atoms form certain kinds of ions and molecules
He called his explanation the octet rule
An octet is a set of 8 and each noble gas, except for helium, has 8 electrons in the highest energy level and a general electron configuration of ns2np6

5. The Octet Rule
When atoms form compounds, they tend to achieve the electron configuration of a noble gas

6. Octet Rule Applied
Atoms of the metallic elements tend to lose their valence electrons leaving a complete octet in the next lowest energy level
Atoms of nonmetallic elements tend to gain electrons or to share electrons with another nonmetallic element to achieve a complete octet
Most elements follow the octet rule, but there are some exceptions

7. Ion Formation
Ion is an atom that has lost or gained a valence electron, resulting in a positive or negative charge
Cation is a positively charged ion
Anion is a negatively charged ion
Both have an electron configuration like a noble gas

8. Formation of Cations
A cation forms when an atom loses 1 or more valence electrons
For metallic elements the name of the cation is the same as the element
For example, a sodium atom forms a sodium cation Na+
Calcium forms a calcium cation Ca2+

9. Formation of Cations Cont.
Although the name is the same, there are chemical differences between an between metals and their cations
For example: Sodium metal reacts explosively with water however sodium cations are quite unreactive
This is why table salt doesn’t explode in your mouth

10. Producers of Cations
The most common cations of the periodic table are produced by metal atoms
Most metal atoms have 1 to 3 valence electrons that can be easily removed
We can represent the electron loss or ionization by drawing the complete electron configuration of the atom and of the ion formed

11. Representing Ionization
Both the sodium ion and the neon atom have 8 electrons in their valence shells
So it is easier to represent the process using electron dot structures

12. Ionization Practice Write an ionization equation for the calcium ion.
Write an ionization equation for the potassium ion.

13. Characteristics of Stable Cations
The name for the cation of a neutral atom is the same as the neutral atom
Both the atom and the ion have the same number of protons and neutrons
An atom and its ion have different chemical properties
Ions have an electrical charge, they form compounds, and conduct electricity when dissolved in water

14. Stable Ions Cont. Many stable ions have noble-gas configurations
Some stable ions do not have noble-gas configuration
For example:
Transition metals often form ions without complete octets
They are also all cations

17. Exceptions to the Rules
Ions with charges higher than 3 are rare
So, some element have to form pseudo noble-gas configurations
Silver, copper, gold, cadmium and mercury are elements with a pseudo noble-gas configuration

18. Pseudo Noble-Gas Configuration

19. Formation of Anions
An anion is a negatively charged ion that is formed by the gaining of electrons
The name of anion of a nonmetallic element is not the same as the element name
The name of the anion typically ends in –ide
For example:
the chlorine atom becomes the chloride ion
The oxygen atom becomes the oxide ion

21. Representing Ionization
The elements that form anions have relatively full valence shells, so it is easier for them to attain noble-gas configurations by gaining electrons

22. Halide Ions
Ions that are produced when atoms of halogens gain electrons are called halide ions
All halogen atoms have 7 valence electrons and only need 1 electron to achieve a noble gas configuration
All halide ions have a charge of 1-

24. Ionization Practice Write an ionization equation for the fluoride ion.
Write an ionization equation for the oxide ion.