Ions And Ionic Bonds

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Notes

Formation of Ions

An **ion** is an electrically charged atom or group of atoms formed by loss or gain of **electrons**.
Atoms gain or lose electrons to obtain a **full outer shell** (noble gas configuration).
**Positive ions (cations)** form when atoms lose electrons (more protons than electrons). Metals form cations.
**Negative ions (anions)** form when atoms gain electrons (more electrons than protons). Non-metals form anions.
Group 1 elements form 1+ ions; Group 2 form 2+ ions; Group 6 form 2– ions; Group 7 form 1– ions.

Ionic Bonding

Ionic bonds form between **metal** and **non-metal** atoms via electron transfer.
Metal atoms lose electrons to become positive ions; non-metal atoms gain electrons to become negative ions.
The oppositely charged ions are held together by strong **electrostatic forces of attraction** – this is the **ionic bond**.
Ionic compounds have no overall charge (total positive charge = total negative charge).
Example: NaCl – Na loses one electron to form Na⁺, Cl gains one electron to form Cl⁻.

Dot-and-Cross Diagrams

Dot-and-cross diagrams show outer-shell electrons only (dots for one atom, crosses for the other).
Each ion is enclosed in **square brackets** with the charge written at the top right.
Example: NaCl – Na⁺ has no outer electrons; Cl⁻ has eight outer electrons.
Example: MgO – Mg loses two electrons to form Mg²⁺; O gains two electrons to form O²⁻.

Lattice Structure (Extended Tier)

Ionic compounds form a **giant lattice structure** – a regular, repeating 3D arrangement of alternating positive and negative ions.
The lattice is held together by strong electrostatic forces in all directions.
Example: NaCl lattice consists of Na⁺ and Cl⁻ ions arranged alternately.

Properties of Ionic Compounds

Ionic compounds are **solid at room temperature** and have **high melting and boiling points**.
High melting/boiling points are due to strong electrostatic forces in the giant lattice requiring much energy to overcome.
**Solid state**: poor electrical conductors because ions are fixed in the lattice and cannot move.
**Molten or aqueous state**: good conductors because ions are free to move and carry charge.
Greater ion charges (e.g., Mg²⁺ and O²⁻) lead to stronger forces and higher melting points than singly charged ions (e.g., Na⁺ and Cl⁻).

Bohr model of a sodium atom (Na) showing electron configuration 2,8,1. Loss of the outer electron forms Na⁺ with configuration 2,8 (like neon).

Bohr model of a chlorine atom (Cl) showing electron configuration 2,8,7. Gain of one electron forms Cl⁻ with configuration 2,8,8 (like argon).

Practice questions

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1.What is an ion?
Easy
- AAn atom with a full outer shell
- BAn electrically charged atom or group of atoms
- CA neutral atom
- DA molecule
2.What is the name for a positive ion?
Easy
3.What is the name for a negative ion?
Easy
4.Complete the sentence:
Easy
An atom that loses electrons becomes $a ____ ion$ .
5.All metals lose electrons to become positively charged ions.
Easy
True or false?
6.What is the charge on an ion formed from a Group 2 element?
Medium
- A3
- B4
- C1
- D2
7.Match each group to the charge on its ion.
Medium
- Group 1
- Group 2
- Group 6
- Group 7
- 1+
- 2+
- 2−
- 1−
8.Which of the following describes the structure of an ionic compound?
Medium
- AA giant lattice of alternating positive and negative ions
- BA simple molecular structure
- CA giant covalent structure
- DA lattice of atoms held by metallic bonds

Slides

What is an Ion?

An ion is an atom or group of atoms that has an electric charge because it has lost or gained electrons.
Atoms form ions to achieve a full outer shell of electrons, like a noble gas.
Positive ions (cations) form when atoms lose electrons; negative ions (anions) form when atoms gain electrons.

What is an ion?

An atom with a full outer shell
An electrically charged atom or group of atoms
A neutral atom
A molecule

Formation of Cations and Anions

Metals lose electrons to form positive ions (cations). For example, sodium (Na) loses one electron to become Na⁺.
Non-metals gain electrons to form negative ions (anions). For example, chlorine (Cl) gains one electron to become Cl⁻.
The charge on an ion can be predicted from the group number: Group 1 → 1⁺, Group 2 → 2⁺, Group 6 → 2⁻, Group 7 → 1⁻.

A sodium atom loses one electron to form $a ____ ion$ with a charge $of ____$ . A chlorine atom gains one electron to form $a ____ ion$ with a charge $of ____$ .

Ionic Bonding

Ionic bonds form between metal and non-metal atoms.
The metal atom loses electrons to become a positive ion; the non-metal gains electrons to become a negative ion.
The oppositely charged ions are held together by strong electrostatic forces of attraction – this is the ionic bond.

Which statement describes ionic bonding?

Sharing of electrons between atoms
Transfer of electrons from a metal to a non-metal
Transfer of electrons from a non-metal to a metal
Strong forces between molecules

Dot-and-Cross Diagrams

Dot-and-cross diagrams show the arrangement of outer-shell electrons in ionic compounds.
Only outer electrons are usually shown; the charge is written at the top right, and square brackets enclose each ion.
Example: NaCl – sodium loses its outer electron to chlorine, forming Na⁺ and Cl⁻.

In a dot-and-cross diagram, the charge is written at $the ____ right-hand$ corner, and the ion is enclosed $in ____$ .

Ionic Compounds and Lattice Structure

Ionic compounds form a giant lattice structure: a regular 3D arrangement of alternating positive and negative ions.
The lattice is held together by strong electrostatic forces in all directions.
The overall charge of an ionic compound is zero because the total positive charge equals the total negative charge.

What holds the ions together in an ionic lattice?

Covalent bonds
Electrostatic forces between oppositely charged ions
Hydrogen bonds
Van der Waals forces

Properties of Ionic Compounds

Ionic compounds have high melting and boiling points due to strong electrostatic forces in the lattice.
They conduct electricity when molten or dissolved in water because ions are free to move.
They do not conduct electricity in the solid state because ions are fixed in position.

Which of these are true about ionic compounds?

They have low melting points.
They conduct electricity when molten.
They conduct electricity in the solid state.
They are usually solid at room temperature.

Explaining Conductivity

In the solid state, ions are held in fixed positions in the lattice and cannot move, so no conduction occurs.
When melted or dissolved, the lattice breaks down and ions become free to move, allowing conduction.
The greater the charge on the ions, the stronger the forces and the higher the melting point (e.g., MgO has a higher melting point than NaCl).

Why do ionic compounds not conduct electricity when solid?

The ions are not charged
The ions are fixed in position and cannot move
The lattice is too small
Electrons are shared

Example: Magnesium Oxide (MgO)

Magnesium (Group 2) loses two electrons to form Mg²⁺.
Oxygen (Group 6) gains two electrons to form O²⁻.
The formula MgO shows a 1:1 ratio because the charges balance: 2⁺ and 2⁻.

In magnesium oxide, the magnesium ion has a charge $of ____ and$ the oxide ion has a charge $of ____$ . The overall charge of the compound $is ____$ .

Which compound would you expect to have a higher melting point: NaCl or MgO?

NaCl
MgO
They are the same
Cannot tell

Summary: Ions and Ionic Bonds

Ions form when atoms lose or gain electrons to achieve a full outer shell.
Metals form positive ions; non-metals form negative ions.
Ionic bonds are strong electrostatic attractions between oppositely charged ions in a giant lattice.
Ionic compounds have high melting points and conduct electricity when molten or dissolved.

Flashcards

What is an ion?

An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons.

Why do atoms form ions?

Atoms form ions to obtain a full outer shell of electrons, like a noble gas.

What is a cation?

A cation is a positively charged ion formed when an atom loses electrons.

What is an anion?

An anion is a negatively charged ion formed when an atom gains electrons.

What type of elements form cations?

Metals lose electrons to form cations (positive ions).

What type of elements form anions?

Non-metals gain electrons to form anions (negative ions).

What is the charge on ions formed by Group 1 elements?

Group 1 elements form ions with a 1+ charge.

What is the charge on ions formed by Group 2 elements?

Group 2 elements form ions with a 2+ charge.

What is the charge on ions formed by Group 6 elements?

Group 6 elements form ions with a 2− charge.

What is the charge on ions formed by Group 7 elements?

Group 7 elements form ions with a 1− charge.

What is an ionic bond?

An ionic bond is the strong electrostatic force of attraction between oppositely charged ions.

Between which types of elements does ionic bonding occur?

Ionic bonding occurs between metal atoms and non-metal atoms.

What is a dot-and-cross diagram?

A dot-and-cross diagram shows the arrangement of outer-shell electrons in an ionic or covalent compound, using dots and crosses.

How is the charge shown in a dot-and-cross diagram for an ion?

The ion is enclosed in square brackets with the charge written at the top right-hand corner.

What is the formula of sodium chloride?

NaCl

Describe the lattice structure of ionic compounds.

Ionic compounds have a giant lattice structure with a regular arrangement of alternating positive and negative ions in 3D.

What is the overall charge of an ionic compound?

An ionic compound has no overall charge; positive and negative charges balance.

What are the typical physical properties of ionic compounds?

Ionic compounds are usually solid at room temperature, have high melting and boiling points, and conduct electricity when molten or in solution but not in solid state.

Why do ionic compounds have high melting points?

They have strong electrostatic forces between oppositely charged ions in a giant lattice, requiring lots of energy to overcome.

Why are ionic compounds poor conductors in the solid state?

In the solid state, ions are in fixed positions and cannot move to carry charge.

Why do ionic compounds conduct electricity when molten or dissolved?

When molten or dissolved, ions are free to move and carry charge.

Which has a higher melting point: NaCl or MgO? Why?

MgO has a higher melting point because Mg²⁺ and O²⁻ have greater charges than Na⁺ and Cl⁻, leading to stronger electrostatic forces.

Write the dot-and-cross diagram for NaCl (outer electrons only).

Na loses its outer electron to Cl; Na⁺ has no outer electrons (shown as [Na]⁺), Cl⁻ has 8 outer electrons (shown as [Cl]⁻ with 8 dots/crosses).

Write the dot-and-cross diagram for MgO.

Mg loses two outer electrons to O; Mg²⁺ has no outer electrons, O²⁻ has 8 outer electrons; formula MgO.

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