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B2.5 · Predict bond type using electronegativity

Learn to predict bond type using electronegativity through clear examples and targeted practice.

Ontario Grade 11 Chemistry

Matter, Chemical Trends, and Chemical Bonding

Ontario Grade 11 Chemistry — Study topic B2.5

Some substances conduct electricity when dissolved in water, while others do not. These observations can be related to the way particles are joined, but an observation alone does not identify a bond type. Electronegativity gives a way to make a prediction: compare how strongly the two bonded atoms attract shared electrons. This lesson uses that comparison to predict a bond type. It does not claim that the prediction alone explains every property of a substance.

What you will learn

Define electronegativity as an atom’s pull on shared bonding electrons.
Use electronegativity values to find the difference between two bonded atoms.
Use the difference to predict whether a bond is non-polar covalent, polar covalent, or ionic.
Explain what the prediction means and recognize that course-level cut-offs are approximate.

1. From atoms to a bond prediction

Atoms can join to form particles. In this lesson, focus on a bond between two atoms. A prerequisite idea is that electrons are negatively charged particles found around an atom’s nucleus. A bond is a connection between atoms that results from their interactions with electrons.

Electronegativity describes how strongly an atom attracts electrons that are shared in a bond. It is a relative value from a reference scale, not a charge and not a count of electrons. A higher electronegativity value means a stronger attraction for shared bonding electrons.

When two bonded atoms have the same or nearly the same electronegativity, neither attracts the shared electrons much more strongly. When their values differ, the more electronegative atom attracts the shared electrons more strongly. The size of the difference is used to predict the bond type.

Electronegativity is an atom’s attraction for electrons shared in a bond.
Compare the two bonded atoms, not unrelated atoms in the substance.
A difference in electronegativity indicates unequal attraction for shared electrons.

2. Use the difference to predict bond type

A course-level electronegativity table gives values for elements. To compare two atoms, subtract the lower value from the higher value. The result is the absolute difference, so it is never negative. Electronegativity values and their difference have no units.

Use the cut-offs supplied by your class or reference table if they differ. A common Grade 11 guide is: a difference from zero to about

0.4

suggests a non-polar covalent bond; a difference above about

0.4

and below about

1.7

suggests a polar covalent bond; and a difference around

1.7

or greater suggests an ionic bond. These boundaries are approximate conventions, not sharp lines in nature.

A covalent bond is a bond in which atoms share electrons. In a non-polar covalent bond, the sharing is approximately even because the atoms attract the shared electrons similarly. In a polar covalent bond, the sharing is uneven because one atom attracts them more strongly. In the course-level model, an ionic bond is predicted when the attraction difference is large enough that the bond is treated as involving electron transfer and oppositely charged ions.

These categories describe a model for predicting bond type. Values close to a boundary can be classified differently by different course tables. Use the cut-offs your teacher or table specifies, and identify the result as a prediction based on that convention.

\Delta EN = |EN_1 - EN_2|

Find the absolute difference between the two electronegativity values.
A small difference predicts non-polar covalent; a middle difference predicts polar covalent; a large difference predicts ionic.
Check the course table’s cut-offs when a value is near a boundary.

3. Read the prediction at the particle level

The difference tells you whether one atom attracts the shared electrons more than the other. For a non-polar covalent prediction, the course model shows the shared electrons as nearly evenly shared. For a polar covalent prediction, the shared electrons are drawn closer to the more electronegative atom. The atoms remain joined by a covalent bond in this model.

For an ionic prediction, the large difference is used to predict that electrons are transferred rather than shared evenly. The resulting particles are ions: atoms or groups of atoms with a net charge. The more electronegative atom is associated with gaining electron density, while the other is associated with losing it. Do not calculate or assign an ion’s charge from the electronegativity difference; use the appropriate course formula information for that.

A bond prediction concerns the pair of atoms being compared. If a substance contains more than one kind of bond, compare each relevant pair separately. The bond-type label is not a claim that every bond is perfectly described by one simple category.

Unequal attraction in a covalent bond means unequal sharing.
A large difference supports an ionic prediction in the Grade 11 model.
Do not use the difference to invent an ion charge or a chemical formula.

4. A careful comparison routine

First, identify the two atoms in the bond. Next, find each atom’s electronegativity in the course reference table. Subtract the lower value from the higher value. Finally, compare the result with the cut-offs and state the predicted bond type.

Keep the calculation separate from the explanation. The number gives the size of the difference; the explanation connects that number to the relative attraction for shared electrons. If you are asked to justify a prediction, name which atom is more electronegative and describe how the electrons are shared or transferred in the course model.

Electronegativity values are usually given to a set number of decimal places. Use the values as printed in the table, and do not add unnecessary digits to the difference. A difference such as

0.3

is a table-based comparison, not a measurement with a physical unit.

Identify, look up, subtract, and classify.
State both the numerical difference and the particle-level reason.
Electronegativity difference has no units.

Common Grade 11 bond-type guide

Electronegativity difference	Predicted bond type	Course-level description
About $0$ to $0.4$	Non-polar covalent	Approximately even sharing
Above about $0.4$ and below about $1.7$	Polar covalent	Uneven sharing
About $1.7$ or greater	Ionic	Electron transfer is used in the model

Worked example

Predicting the bond in hydrogen chloride

A course reference table lists electronegativity values of

2.1

for hydrogen and

3.0

for chlorine. Use the common Grade 11 cut-offs in this lesson to predict the bond type in hydrogen chloride.

Identify the comparison
The bond joins hydrogen and chlorine, so compare the electronegativity values for those two atoms.
Calculate the difference
Subtract the lower table value from the higher one. Electronegativity has no units, so the difference has no units either.
$\Delta EN = |3.0 - 2.1| = 0.9$
Classify and explain
The difference, $0.9$ , is above about $0.4$ and below about $1.7$ . The bond is therefore predicted to be polar covalent using these cut-offs. Chlorine attracts the shared electrons more strongly than hydrogen, so the sharing is uneven in the course-level model.

Answer: The hydrogen–chlorine bond is predicted to be polar covalent.

Check: The calculation uses the two table values, gives a non-negative difference, and places it in the stated polar covalent range.

Common mistakes and how to avoid them

Subtracting in an order that gives a negative difference.

Correction: Subtract the smaller electronegativity from the larger one, or use the absolute difference.

Calling a bond ionic simply because the two atoms have different electronegativities.

Correction: All comparisons may show some difference. Use the size of the difference and the course cut-offs to make the prediction.

Treating the cut-offs as exact laws.

Correction: They are approximate course conventions. Follow the table used in class, especially near a boundary.

Saying that a polar covalent bond has transferred electrons and formed ions.

Correction: In the course model, polar covalent means electrons are shared unevenly. A large difference is used to predict an ionic bond.

Treating electronegativity as an atom’s charge or as the number of electrons it has.

Correction: Electronegativity describes attraction for shared bonding electrons. It is not a charge or an electron count.

Lesson summary

Electronegativity describes an atom’s attraction for electrons shared in a bond.
Find the absolute difference between the two bonded atoms’ values.
Use the course cut-offs to predict non-polar covalent, polar covalent, or ionic bonding.
Explain the prediction by describing whether the electrons are shared approximately evenly, shared unevenly, or treated as transferred.
The cut-offs are approximate, and electronegativity differences have no units.

Check your understanding

Question 1

A bond has an electronegativity difference of

0.2

. What bond type is predicted using the guide in this lesson?

Non-polar covalent
Polar covalent
Ionic
correctIndex":0,"explanation":"A difference of $0.2$ is in the approximate zero-to- $0.4$ range, so the guide predicts a non-polar covalent bond."

Show answer and explanation

Non-polar covalent

A difference of

0.2

is in the approximate zero-to-

0.4

range, so the guide predicts a non-polar covalent bond.

Question 2

Atom

A

has electronegativity

1.8

and atom

B

has electronegativity

2.6

. What is the difference?

$0.8$
$-0.8$
$4.4$
correctIndex":0,"explanation":"Subtract the smaller value from the larger: $|2.6 - 1.8| = 0.8$ . The difference is non-negative."},{

Show answer and explanation

0.8

Subtract the smaller value from the larger:

|2.6 - 1.8| = 0.8

. The difference is non-negative.

Question 3

A difference is well above the approximate ionic cut-off. Which statement best matches the course-level prediction?

The bond is predicted to be ionic, with electron transfer represented in the model.
The bond is predicted to be non-polar covalent, with equal attraction.
The electronegativity values show the exact charge of each atom.
correctIndex":0,"explanation":"A large difference supports an ionic prediction. The difference itself does not give exact ion charges."},{

Show answer and explanation

The bond is predicted to be ionic, with electron transfer represented in the model.

A large difference supports an ionic prediction. The difference itself does not give exact ion charges.

Key terms

Electronegativity: A relative value describing how strongly an atom attracts electrons shared in a bond.
Electronegativity difference: The non-negative result found by subtracting the lower electronegativity value from the higher one.
Covalent bond: A bond in which atoms share electrons.
Non-polar covalent bond: A covalent bond with approximately even sharing of electrons in the course-level model.
Polar covalent bond: A covalent bond with uneven sharing of electrons because one atom attracts them more strongly.
Ionic bond: A bond predicted from a large electronegativity difference, represented in the course model through electron transfer and oppositely charged ions.
Ion: An atom or group of atoms with a net electric charge.

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About this lesson and its review

Published by DoAssignment. This reviewed lesson follows Ontario Grade 11 Chemistry (SCH3U), expectation B2.5. It is a study resource, not an official curriculum publication.

Before publication, content is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability. Errors can still occur, so corrections are welcomed.

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