1. Chapter 5
Section 1 Simple Ions
Objectives
Relate the electron configuration of an atom to its chemical reactivity.
Determine an atom’s number of valence electrons, and use the octet rule to predict what stable ions the atom is likely to form.
Explain why the properties of ions differ from those of their parent atoms.

2. Chapter 5 Chemical Reactivity
Section 1 Simple Ions
Chemical Reactivity
How much an element reacts depends on the electron configuration of its atoms.
For example, oxygen will react with magnesium. In the electron configuration for oxygen, the 2p orbitals, which can hold six electrons, have only four:
[O] = 1s22s22p4
Neon has no reactivity. Its 2p orbitals are full:
[Ne] = 1s22s22p6

3. Chemical Reactivity, continued
Chapter 5
Section 1 Simple Ions
Chemical Reactivity, continued
Noble Gases Are the Least Reactive Elements
Neon is a noble gas.
The noble gases, which are found in Group 18 of the periodic table, show almost no chemical reactivity.
The noble gases have filled outer energy levels.
This electron configuration can be written as ns2np6 where n represents the outer energy level.

4. Chemical Reactivity, continued
Chapter 5
Section 1 Simple Ions
Chemical Reactivity, continued
Noble Gases Are the Least Reactive Elements, continued
The eight electrons in the outer energy level fill the s and p orbitals, making these noble gases stable.
In most chemical reactions, atoms tend to match the s and p electron configurations of the noble gases.
This tendency to have either empty outer energy levels or full outer energy levels of eight electrons is called the octet rule.

5. Chapter 5
Visual Concepts
The Octet Rule

6. Chemical Reactivity, continued
Chapter 5
Section 1 Simple Ions
Chemical Reactivity, continued
Alkali Metals and Halogens Are the Most Reactive Elements
An atom whose outer s and p orbitals do not match the electron configurations of a noble gas will react to lose or gain electrons so the outer orbitals will be full.
When added to water, an atom of potassium (an alkali metal) gives up one electron in its outer energy level.
Then, it has the s and p configuration of a noble gas.
1s22s22p63s23p64s1 1s22s22p63s23p6

7. Chemical Reactivity, continued
Chapter 5
Section 1 Simple Ions
Chemical Reactivity, continued
Alkali Metals and Halogens Are the Most Reactive Elements, continued
Calcium, a halogen, is also very reactive.
An atom of calcium has seven electrons in its outer energy level.
By gaining just one electron, it will have the s and p configuration of a noble gas.
1s22s22p63s23p s22s22p63s23p6

8. Chapter 5 Valence Electrons
Section 1 Simple Ions
Valence Electrons
Potassium after it loses one electron has the same electron configuration as chlorine after it gains one.
Both are the same as that of the noble gas argon.
[Ar] = 1s22s22p63s23p6
The atoms of many elements become stable by achieving the electron configuration of a noble gas.
The electrons in the outer energy level are known as valence electrons.

9. Chapter 5
Visual Concepts
Valence Electrons

10. Valence Electrons, continued
Chapter 5
Section 1 Simple Ions
Valence Electrons, continued
Periodic Table Reveals an Atom’s Number of Valence Electrons
To find out how many valence electrons an atom has, check the periodic table.
For example, the element magnesium, Mg, has the following electron configuration:
[Mg] = [Ne]3s2
This configuration shows that a magnesium atom has two valence electrons in the 3s orbital.

11. Valence Electrons, continued
Chapter 5
Section 1 Simple Ions
Valence Electrons, continued
Periodic Table Reveals an Atom’s Number of Valence Electrons, continued
The electron configuration of phosphorus, P, is [Ne]3s23p3.
Each P atom has five valence electrons: two in the 3s orbital and three in the 3p orbital.

12. Valence Electrons, continued
Chapter 5
Section 1 Simple Ions
Valence Electrons, continued
Atoms Gain Or Lose Electrons to Form Stable Ions
All atoms are uncharged because they have equal numbers of protons and electrons.
For example, a potassium atom has 19 protons and 19 electrons.
After giving up one electron, potassium still has 19 protons but only 18 electrons.
Because the numbers are not the same, there is a net electrical charge.

13. Valence Electrons, continued
Chapter 5
Section 1 Simple Ions
Valence Electrons, continued
Atoms Gain Or Lose Electrons to Form Stable Ions,
continued
An ion is an atom, radical, or molecule that has gained or lost one or more electrons and has a negative or positive charge.
The following equation shows how a potassium atom forms an ion with a 1+ charge.
K  K+ + e
An ion with a positive charge is called a cation.

14. Chapter 5
Visual Concepts
Ion

15. Valence Electrons, continued
Chapter 5
Section 1 Simple Ions
Valence Electrons, continued
Atoms Gain Or Lose Electrons to Form Stable Ions,
continued
In the case of chlorine, far less energy is required for an atom to gain one electron rather than give up its seven valence electrons to be more stable.
The following equation shows how a chlorine atom forms an ion with a 1− charge.
Cl + e → Cl
An ion with a negative charge is called an anion.

16. Comparing Cations and Anions
Chapter 5
Visual Concepts
Comparing Cations and Anions

17. Valence Electrons, continued
Chapter 5
Section 1 Simple Ions
Valence Electrons, continued
Characteristics of Stable Ions
Both an atom and its ion have the same number of protons and neutrons, so the nuclei are the same.
The chemical properties of an atom depend on the number and configuration of its electrons.
Therefore, an atom and its ion have different chemical properties.

18. Valence Electrons, continued
Chapter 5
Section 1 Simple Ions
Valence Electrons, continued
Many Stable Ions Have Noble-Gas Configurations
Many atoms can form stable ions with a full octet. For example, Ca, forms a stable ion.
The electron configuration of a calcium atom is:
[Ca] = 1s22s22p63s23p64s2
By giving up its two valence electrons in the 4s orbital, it forms a stable cation with a 2+ charge:
[Ca2+] = 1s22s22p63s23p6
This electron configuration is like that of argon.

19. Some Ions with Noble-Gas Configurations
Chapter 5
Section 1 Simple Ions
Some Ions with Noble-Gas Configurations

20. Valence Electrons, continued
Chapter 5
Section 1 Simple Ions
Valence Electrons, continued
Some Stable Ions Do Not Have Noble-Gas Configurations
Not all stable ions have an electron configuration like those of noble gases. Transition metals often form ions without complete octets.
With the lone exception of rhenium, Re, the stable transition metal ions are all cations.
Also, some elements, mostly transition metals, form stable ions with more than one charge.

21. Stable Ions Formed by the Transition Elements and Some Other Metals
Chapter 5
Section 1 Simple Ions
Stable Ions Formed by the Transition Elements and Some Other Metals

22. Chapter 5
Section 1 Simple Ions
Atoms and Ions
Having identical electron configurations does not mean that a sodium cation is a neon atom.
They still have different numbers of protons and neutrons.
Ions and Their Parent Atoms Have Different Properties
Both sodium and chlorine are very reactive.
When they are mixed, a violent reaction takes place, producing a white solid—table salt (sodium chloride).
It is made from sodium cations and chloride anions.

23. Atoms and Ions, continued
Chapter 5
Section 1 Simple Ions
Atoms and Ions, continued
Atoms of Metals and Nonmetal Elements Form Ions Differently
Nearly all metals form cations. For example, magnesium metal, Mg, has the electron configuration:
[Mg] = 1s22s22p63s2
To have a noble-gas configuration, the atom must either gain six electrons or lose two.
Losing two electrons requires less energy than gaining six.

24. Atoms and Ions, continued
Chapter 5
Section 1 Simple Ions
Atoms and Ions, continued
Atoms of Metals and Nonmetal Elements Form Ions Differently, continued
The atoms of all nonmetal elements form anions. For example, oxygen, O, has the electron configuration:
[O] = 1s22s22p4
To have a noble-gas configuration, an oxygen atom must either gain two electrons or lose six.
Acquiring two electrons requires less energy than losing six.