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B2.1 · Use periodic-trend and chemical-bonding terminology

Learn to use periodic-trend and chemical-bonding terminology through clear examples and targeted practice.

Ontario Grade 11 Chemistry

Matter, Chemical Trends, and Chemical Bonding

Using Grade 11 language to describe patterns in atoms and bonds

A metal can be shaped into a wire, while a salt crystal is brittle and table sugar can dissolve in water. These observations are linked to how particles are arranged and held together. Before describing those links, it helps to know how the periodic table organizes elements and how chemists name patterns in their properties. This lesson focuses on using that terminology accurately, not on explaining every property of every substance.

What you will learn

Define and use key terms for periodic trends.
Describe how selected properties change across a period and down a group.
Use electronegativity and element type to describe chemical bonding.
Distinguish ionic, covalent, and metallic bonding using course-level terminology.

1. Prerequisite bridge: reading the periodic table

The periodic table arranges elements by atomic number. An element’s atomic number is the number of protons in its atoms. A horizontal row is called a period. A vertical column is called a group. Elements in the same group have similar chemical properties, so a group is a useful place to compare elements.

An atom has a small, positively charged nucleus and negatively charged electrons around it. For this course-level model, electrons occupy energy levels, sometimes called shells. The outermost occupied energy level contains the valence electrons. Valence electrons are important when describing how atoms bond.

A periodic trend is a pattern in a property as you move across a period or down a group. A trend describes a general pattern. It does not mean that every element has exactly the same change as its neighbour.

A period is a row; a group is a column.
Valence electrons are the electrons in the outermost occupied energy level.
A periodic trend is a general pattern across a period or down a group.

2. Describing periodic trends

Atomic radius is a measure of the size of an atom. For elements in the same period, atomic radius generally decreases from left to right. The atoms gain protons while electrons are added to the same main energy level. The stronger attraction between the nucleus and the electrons in that level draws the electron cloud closer overall. Down a group, atomic radius generally increases because each step adds another occupied energy level.

Ionization energy is the energy needed to remove an electron from a gaseous atom. In general, it increases from left to right across a period and decreases down a group. Across a period, the attraction between the nucleus and the outer electrons tends to increase. Down a group, the outer electrons are farther from the nucleus and are more shielded by inner electrons, so they are generally easier to remove. Shielding means that inner electrons reduce the nucleus’s pull on outer electrons.

Electronegativity describes how strongly an atom attracts shared electrons in a chemical bond. It generally increases from left to right across a period and decreases down a group. It is a relative value used to compare atoms in bonds. It is not the same as ionization energy: ionization energy concerns removing an electron from a gaseous atom, while electronegativity concerns attraction for shared electrons in a bond.

Metallic character describes how strongly an element shows the usual properties of metals. It generally increases down a group and toward the left side of the periodic table. Non-metallic character generally increases toward the upper right. These are broad trends. Use the periodic table and course reference materials when a question asks about a specific element.

Across a period: atomic radius decreases; ionization energy and electronegativity increase

Atomic radius generally decreases across a period and increases down a group.
Ionization energy generally increases across a period and decreases down a group.
Electronegativity generally increases across a period and decreases down a group.
Metallic character generally increases down and toward the left.

3. From atoms to bonding terms

A chemical bond is an attraction that holds particles together in a substance. The periodic table helps describe the kinds of bonding that are commonly found. The terms name useful models; real substances can have details that are more complex than a short label suggests.

An ionic bond is the attraction between oppositely charged ions. Ions are particles with a net charge because they have gained or lost electrons. In the Grade 11 model, ionic bonding commonly occurs between a metal and a non-metal. The metal forms a positive ion and the non-metal forms a negative ion. For example, in sodium chloride, the particles are represented as sodium ions and chloride ions, not as separate neutral sodium and chlorine atoms joined in pairs.

A covalent bond forms when atoms share electrons. Covalent bonding commonly occurs between non-metal atoms. A molecule is a discrete group of atoms joined by covalent bonds; water molecules are one example. In a polar covalent bond, the shared electrons are attracted more strongly to one atom than to the other. In a non-polar covalent bond, they are shared more evenly. Electronegativity is useful language for describing this difference.

A metallic bond is the attraction between positive metal ions and mobile, shared valence electrons in a metal. This course-level model helps describe why metals can conduct electricity and can be shaped without breaking into separate molecules. Do not describe metallic bonding as a set of covalent molecules.

Bond type and substance properties are connected, but one observation alone may not identify a bond. For instance, many ionic compounds are crystalline solids, but identifying a substance requires more evidence than appearance alone.

Ionic bonding involves attraction between oppositely charged ions.
Covalent bonding involves shared electrons between atoms.
Metallic bonding involves positive metal ions and mobile valence electrons.
Electronegativity helps describe how evenly shared electrons are attracted in a covalent bond.

4. Choosing precise terminology

When describing a trend, state the direction of movement and the property. For example, say that atomic radius generally increases down a group. Avoid saying only that an element is “bigger” without naming the property or the comparison.

When describing bonding, identify the particles and the attraction or sharing involved. For an ionic substance, name positive and negative ions and their attraction. For a covalent substance, say that atoms share electrons. For a metal, describe positive metal ions and mobile valence electrons.

These models use different language because they describe different particle arrangements. A chemical formula can show the kinds and ratios of atoms or ions, but the formula alone does not always show every detail of bonding. Choose terminology that matches the type of substance and the question.

Name the property and direction when stating a periodic trend.
Name the particles and how they interact when describing a bond.
Do not use “share” as a substitute for describing ionic attraction.

Worked example

Comparing sodium and chlorine

Use periodic-trend and bonding terminology to compare sodium and chlorine in sodium chloride.

Locate the elements
Sodium is a metal on the left side of Period 3. Chlorine is a non-metal farther to the right in the same period. This lets us use across-a-period trends for a general comparison.
Apply the trend terms
Across Period 3, atomic radius generally decreases, while ionization energy and electronegativity generally increase. Therefore, chlorine has a smaller atomic radius and a higher electronegativity than sodium in this course-level comparison.
$r_{\mathrm{Na}} > r_{\mathrm{Cl}},\quad \chi_{\mathrm{Na}} < \chi_{\mathrm{Cl}}$
Describe the bonding
Sodium is a metal and chlorine is a non-metal. Sodium chloride is described as an ionic compound. Use the terms positive sodium ions, negative chloride ions, and attraction between oppositely charged ions. This description uses the ionic-bonding model rather than describing sodium and chlorine atoms as sharing electrons.
$\mathrm{Na^+},\ \mathrm{Cl^-}$

Answer: Chlorine has a smaller atomic radius and higher electronegativity than sodium in this same-period comparison. Sodium chloride is described as an ionic compound, with attraction between positive sodium ions and negative chloride ions.

Check: The comparison uses trends in the correct directions. The bonding description names ions and their attraction, rather than shared electrons.

Common mistakes and how to avoid them

Saying that atomic radius increases from left to right across a period.

Correction: The general trend is that atomic radius decreases from left to right and increases down a group.

Calling electronegativity the energy needed to remove an electron.

Correction: That definition is ionization energy. Electronegativity describes attraction for shared electrons in a bond.

Describing ionic bonding as atoms sharing electrons.

Correction: Use “sharing” for covalent bonding. Describe ionic bonding as attraction between oppositely charged ions.

Describing metallic bonding as positive metal ions joined into separate molecules.

Correction: Use the course-level model of positive metal ions attracted to mobile, shared valence electrons.

Lesson summary

A period is a row, and a group is a column of the periodic table.
Atomic radius generally decreases across a period and increases down a group.
Ionization energy and electronegativity generally increase across a period and decrease down a group.
Ionic bonding describes attraction between oppositely charged ions; covalent bonding describes shared electrons; metallic bonding describes positive metal ions and mobile valence electrons.
Precise descriptions name the property, direction, particles, and type of interaction.

Check your understanding

Question 1

Which statement gives the general trend in atomic radius?

It increases across a period and decreases down a group.
It decreases across a period and increases down a group.
It increases both across a period and down a group.
It does not change across periods or down groups.

Show answer and explanation

It decreases across a period and increases down a group.

The general pattern is a decrease from left to right across a period and an increase down a group.

Question 2

Which phrase best describes covalent bonding?

Attraction between oppositely charged ions
Attraction between positive metal ions and mobile electrons
Sharing of electrons between atoms
Removal of an electron from a gaseous atom

Show answer and explanation

Sharing of electrons between atoms

Covalent bonds involve atoms sharing electrons. The other choices describe ionic bonding, metallic bonding, and ionization energy.

Question 3

What does electronegativity describe?

An atom’s size
An atom’s attraction for shared electrons in a bond
The energy needed to remove an electron from a gaseous atom
The number of protons in an atom

Show answer and explanation

An atom’s attraction for shared electrons in a bond

Electronegativity describes attraction for shared electrons in a bond. The energy needed to remove an electron is ionization energy.

Key terms

Atomic radius: A measure of the size of an atom.
Chemical bond: An attraction that holds particles together in a substance.
Electronegativity: A measure of how strongly an atom attracts shared electrons in a chemical bond.
Group: A vertical column in the periodic table.
Ion: A particle with a net charge because it has gained or lost electrons.
Ionization energy: The energy needed to remove an electron from a gaseous atom.
Metallic character: The degree to which an element shows the usual properties of metals.
Period: A horizontal row in the periodic table.

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Published by DoAssignment. This AI-assisted lesson follows Ontario Grade 11 Chemistry (SCH3U), expectation B2.1. It is a study resource, not an official curriculum publication.

Before publication, the draft is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability, and then requires administrator approval. Errors can still occur, so corrections are welcomed.

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