Lewis Structure

Learning Competency:
 Draw the Lewis Structure of Ions.
1
Learning objectives:
To learn more about the topic we will attain these objectives:

1. Draw the Lewis electron dot structure of atoms and ions.
2. Determine the charge of the ions based from their group
number and valence electrons.
3. Identify elements that will form cations and anions based
on their ionization energy and electron affinity.
4. Explain the formation of ionic compounds.
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Lewis Structure of
Ions
Quiz Game
Let’s start with…
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Concept in a BOX
gain
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Lewis Dot Structure
▸ Ions - atom or group of atoms that has an electric charge.
▸ Cations - ion with positive charge.
▸ Anions - ion with negative charge.
▸ Lewis Electron Dot Symbols (LEDS) - a representation of
the valence electrons of an atom that uses dots around the
symbol of the element.
▸ Ionic compounds - form when an atom gains or loses
electrons.
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Lewis Dot Structure
▸ Gilbert N. Lewis developed a system of representing
valence electrons in an atom known as Lewis electron-dot
structure (LEDS) or simply Lewis Structure.
▸ A Lewis structure is composed of a symbol of an element
represents the nucleus and inner electrons surrounded by
dots which represent the valence electrons.
▸ Valence electrons are atoms in the outermost shell used to
form chemical bonds. They are better represented with the
Lewis dot symbols.
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Lewis Dot Structure
▸ According to Lewis, atoms combine in order to achieve a
more stable electron configuration. And this maximum
stability is attained when an atom is isoelectronic with a
noble gas.
▸ The Octet Rule states that when atoms of elements
combine to form compounds, they tend to lose, gain, or
share electrons to achieve the same electron arrangement
as the noble gas nearest them in the periodic table.
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Lewis Dot Structure
For representative elements, the group number corresponds

to the number of valence electrons.
▸ Place one dot at a time on the four sides (top, right,
bottom, left) of the element symbol.
▸ Keep adding dots, pairing the dots until all are used up.
▸ The specific placement of dots is not important.
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Lewis Dot Structure
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Lewis Dot Structure for Ions
▸ Ions are formed when there is unequal number of protons and
electrons. When a neutral atom loses electron, it becomes a
cation. If an atom gains an electron it will become an anion.
▸ Ionization Energy (IE) is the amount of energy required to
remove an electron.
▸ Elements under Group 1A have the lowest ionization energy in
every period while elements under Group 8A have the highest
ionization energy in every period.
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▸ For a metal, the total number of dots is the maximum number of
electrons an atom loses to form a cation with a positive (+)
charge.
▸ Steps in drawing the Lewis structures of ions:
Step 1. Determine the valence electrons of every atom.
Step 2. Determine how many electrons are lost or gained.
Assign a positive (+) charge for ion which loses electrons
and negative (-) charge for ion which gains electrons.
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▸ Example: Let’s consider Sodium atom.
Step 1. Determine the valence electrons of every atom.
Sodium is under group 1A (1 valence electron)
Sodium is a metal that will lose one valence electron in
order to become stable.
-e-
Na • Na +
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▸ Electron Affinity (EA) is the energy released when an atom

accepts an electron.
▸ Elements on the right side of the periodic table which are mostly
nonmetals have a higher tendency to accept electrons forming
anions with a negative (-) charge.
▸ Generally, ionization energy measures the energy change when
an atom loses an electron while electron affinity measures the
energy change when an atom gains an electron.
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▸ For a nonmetal, the number of unpaired dots is the number

of electrons that become paired either through electron
gain or through electron sharing to form an anion with a
negative (-) charge.
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▸ Example: Let’s consider Chlorine atom.
Step 1. Determine the valence electrons of every atom. Chlorine

is under group 7A (7 valence electrons).
Chlorine is a nonmetal that will gain one valence electron in order
to become stable.
+e-
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Sample Problem.
What you need: Periodic table
What to do: Complete the table with the information required.
Number of
Lewis Structure
Group Valence Metal/ Electrons
Element Electrons Nonmetal
Number Neutral
Ion Gained Lost
Atom
Potassium 1A 1 Metals K• K+ 1
Carbon
Magnesium
Oxygen
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Ionic Compounds and Lewis Structures
▸ Ionic bonding generally exists between a metal and a

nonmetal as a result of their high electronegativity
difference. Recall that electronegativity is a measure of an
atom’s ability to attract electrons.
▸ Compounds formed as a result of ionic bonding are

classified as ionic compounds.
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▸ The formation of ionic compounds may be represented

using Lewis Structures. For example, one sodium atom
with one valence electron is enough to complete the octet of
one chlorine atom and form a formula unit of sodium
chloride (NaCl).
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▸ In forming a compound between magnesium and chlorine,
the magnesium atom needs to lose its two valence electrons
to form an octet. Thus, it needs two chlorine atoms, each
accommodating only one additional electron to complete an
octet, to form a formula unit of magnesium chloride
(MgCl2).
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Properties of Ionic Compounds
The ionic charge present on the atoms or polyatomic ions
present in an ionic compound holds the atoms in place
strongly in the compound. This ionic bond is so strong that
ionic compounds typically have the following properties:
▸ High melting points
▸ High boiling points
▸ A crystal lattice structure
▸ Solids break easily into sheets
▸ Solids do not conduct electricity and are good insulators
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Reflection
1. How are ions formed?

2. If you were an element, which group would you choose?
Do you want to be a giver or a receiver? Why? And how
can you relate it to your relationship with your family,
friends and loved ones?
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Generalizations
1. Which type of elements will likely to form a

cation? Anion?
2. How are cations and anions formed?
3. What did you notice about the charge of the ion?
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Thank
You!
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Lewis Structure

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Learning Competency:

 Draw the Lewis Structure of Ions.

To learn more about the topic we will attain these objectives:

For representative elements, the group number corresponds

▸ Electron Affinity (EA) is the energy released when an atom

▸ For a nonmetal, the number of unpaired dots is the number

Step 1. Determine the valence electrons of every atom. Chlorine

▸ Ionic bonding generally exists between a metal and a

▸ Compounds formed as a result of ionic bonding are

▸ The formation of ionic compounds may be represented

1. How are ions formed?

1. Which type of elements will likely to form a

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