Ions & 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 lose or gain electrons to obtain a **full outer shell** (noble gas configuration).
**Cations** are positive ions formed when atoms **lose** electrons (metals).
**Anions** are negative ions formed when atoms **gain** electrons (non-metals).
Group 1 elements form 1+ ions; Group 2 form 2+ ions.
Group 6 elements form 2– ions; Group 7 form 1– ions.

Ionic Bonding

Ionic bonding occurs between **metal** and **non-metal** atoms.
Metal atoms lose electrons to non-metal atoms, forming positive and negative ions.
The oppositely charged ions are held together by **strong electrostatic forces of attraction**.
This electrostatic attraction is the **ionic bond**.
The overall charge of an ionic compound is **zero**.

Dot-and-Cross Diagrams

Dot-and-cross diagrams show the arrangement of **outer-shell electrons** only.
Electrons from one atom are shown as **dots**, from the other as **crosses**.
Each ion is enclosed in **square brackets** with the charge written at the top right.
Example: NaCl – Na loses one electron (becomes Na⁺), Cl gains one electron (becomes Cl⁻).

Ionic Lattice Structure (Extended)

Ionic compounds form a **giant lattice structure**.
The lattice consists of a **regular arrangement** of alternating positive and negative ions.
Strong electrostatic forces act in **all directions** between oppositely charged ions.
Example: NaCl lattice – each Na⁺ is surrounded by Cl⁻ and vice versa.

Properties of Ionic Compounds

Ionic compounds are **solid at room temperature**.
They have **high melting and boiling points** due to strong electrostatic forces.
They **conduct electricity** when **molten or in aqueous solution** (ions free to move).
They do **not conduct electricity** when **solid** (ions fixed in lattice).
Higher charge on ions leads to **stronger forces** and higher melting point (e.g., MgO > NaCl).

Bohr model of a sodium atom (2.8.1). It loses one electron to form Na⁺ (2.8).

Bohr model of a chlorine atom (2.8.7). It gains one electron to form Cl⁻ (2.8.8).

Practice questions

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1.What change occurs to an atom when it forms a negative ion?
Easy
- AIt loses electrons.
- BIt gains protons.
- CIt gains electrons.
- DIt loses protons.
2.Which of the statements describes ionic bonding?
Easy
- AElectrostatic attraction between atoms
- BElectrostatic attraction between positively charged particles and delocalised electrons
- CElectrostatic attraction between oppositely charged ions
- DElectrostatic attraction between the nuclei of two atoms and a shared pair of electrons
3.The electronic configuration of an ion was determined to be 2.8.8. What could the identity of the ion be?
Medium
- ACa²⁺
- BS²⁻
- CBoth Ca²⁺ and S²⁻
- DNeither Ca²⁺ nor S²⁻
4.Calcium reacts with fluorine to form calcium fluoride. Which statement describes what happens to calcium atoms in this reaction?
Medium
- ACalcium ions lose electrons to form positive charges.
- BCalcium atoms gain 3 electrons to form positive ions.
- CCalcium ions gain 2 electrons to form positive ions.
- DCalcium atoms lose 2 electrons to form positive ions.
5.Three statements about sodium chloride are shown. 1. Sodium chloride has a low melting point because the attractive forces between the ions in the lattice are weak. 2. Sodium chloride conducts electricity in aqueous solution because the ions are free to move. 3. Sodium chloride conducts electricity when solid because the ions can carry an electric current through the lattice. Which statements are correct?
Medium
- A1 and 2
- B2 only
- C2 and 3
- D3 only
6.Ionic compounds are formed when a metal reacts with a nonmetal. Which two elements combine to form this kind of compound? Element Q: electronic structure 2.4 Element R: electronic structure 2.8 Element S: electronic structure 2.8.1 Element T: electronic structure 2.8.7
Hard
- AS and T
- BR and S
- CQ and R
- DQ and T
7.Ionic compounds are formed when metals react with nonmetals. Which row correctly describes the electron transfer when an ionic bond is formed and the nature of the bond?
Hard
- AMetal to nonmetal; Opposite ions attract
- BMetal to nonmetal; Opposite ions repel
- CMetal to metal; Same ions repel
- DNonmetal to metal; Opposite ions attract
8.Potassium and bromine chemically combine to form the compound potassium bromide. During formation, each bromine atom …..1….. one electron which is completely …..2….. from the outer shell of the potassium atom. The …..3….. force of attraction is formed from the attraction between the opposite charges on each ion. What words correctly fill gaps 1, 2 and 3?
Hard
- Aloses; shared; electrical
- Bloses; transferred; intermolecular
- Cgains; shared; electrostatic
- Dgains; transferred; electrostatic

More questions

9.The bonding present in a substance determines the structure and properties of that substance. Which of the following statements is a correct description of the structure of an ionic compound?
Hard
- AA lattice structure with an irregular arrangement of alternating positive and negative ions
- BA lattice structure with a regular arrangement of alternating positive and negative ions
- CA random structure with a regular arrangement of alternating positive and negative ions
- DA random structure with an irregular arrangement of alternating positive and negative ions
10.Extended Only: The ionic lattice structure of potassium chloride is shown below. Which of the following statements best describes the bonding and structure of KCl?
Hard
- AA small lattice structure held together by electrostatic forces between oppositely charged ions which act in all directions.
- BA small lattice structure held together by electrostatic forces between like charged ions which act in all directions.
- CA giant lattice structure held together by electrostatic forces between oppositely charged ions which act in all directions.
- DA giant lattice structure held together by electrostatic forces between oppositely charged ions which act in one direction only.
11.What is an ion?
Easy
- AAn atom that has gained or lost protons
- BAn atom that has gained or lost neutrons
- CAn electrically charged atom or group of atoms formed by the loss or gain of electrons
- DA neutral atom with a full outer shell
12.What is the charge on an ion formed from a Group 2 element?
Easy
- A1+
- B2+
- C1-
- D2-
13.The table shows the melting points and electrical conductivities of four substances. Which substance is most likely an ionic compound? | Substance | Melting point (°C) | Conducts electricity when solid | Conducts electricity when molten | |-----------|--------------------|--------------------------------|----------------------------------| | W | 3550 | no | no | | X | 801 | no | yes | | Y | -91 | no | no | | Z | 3410 | yes | yes |
Medium
- AW
- BX
- CY
- DZ
14.An atom of element X has electronic configuration 2.8.2. An atom of element Y has electronic configuration 2.8.7. What is the formula of the ionic compound formed when X and Y react?
Medium
- AXY
- BXY2
- CX2Y
- DX2Y3
15.The electronic configurations of atoms P and Q are shown. P: 2.8.1 Q: 2.8.7 P and Q combine by ionic bonding. What is the formula of the compound produced?
Hard
- AP2Q
- BPQ2
- CPQ
- DP2Q3
16.Which statement explains why ionic compounds have high melting points?
Medium
- AThey have weak intermolecular forces between molecules.
- BThey have strong electrostatic forces between oppositely charged ions in a giant lattice.
- CThey have strong covalent bonds between atoms.
- DThey have weak forces between ions that require little energy to overcome.
17.A student tests the electrical conductivity of an ionic compound in three states: solid, molten, and dissolved in water. Which row shows the correct results? | State | Conducts electricity? | |-------|----------------------| | Solid | no | | Molten| yes | | Aqueous| yes |
Hard
- ASolid: no, Molten: yes, Aqueous: yes
- BSolid: yes, Molten: yes, Aqueous: yes
- CSolid: no, Molten: no, Aqueous: yes
- DSolid: yes, Molten: no, Aqueous: no
18.Which two elements are most likely to form an ionic compound? Element A: electronic configuration 2.8.1 Element B: electronic configuration 2.8.7 Element C: electronic configuration 2.8.8 Element D: electronic configuration 2.4
Easy
- AA and B
- BA and C
- CB and D
- DC and D
19.The diagram shows the electronic configurations of two atoms. Which dot-and-cross diagram correctly represents the ionic compound formed? (Assume the outer shells are shown: Atom X: 2.8.2, Atom Y: 2.8.6)
Hard
- AX loses 2 electrons to Y, forming X2+ and Y2-, with both ions having full outer shells.
- BX gains 2 electrons from Y, forming X2- and Y2+.
- CX loses 1 electron to Y, forming X+ and Y-.
- DX shares 2 electrons with Y, forming a covalent bond.
20.Which statement about the lattice structure of an ionic compound is correct?
Medium
- AIt consists of a regular arrangement of alternating positive and negative ions.
- BIt consists of a random arrangement of positive and negative ions.
- CIt consists of a regular arrangement of molecules held by intermolecular forces.
- DIt consists of a giant covalent network of atoms.
21.What is the charge on an ion formed from a Group 6 element?
Easy
- A1+
- B2+
- C1-
- D2-
22.A student measures the electrical conductivity of an ionic compound at different temperatures. The results show no conductivity at 25°C, but conductivity increases sharply at 800°C. What is the most likely explanation?
Hard
- AAt 25°C the ions are fixed in the lattice; at 800°C the compound has melted and ions are free to move.
- BAt 25°C the compound is a gas; at 800°C it becomes a liquid.
- CAt 25°C the electrons are delocalised; at 800°C they become localised.
- DAt 25°C the compound is covalent; at 800°C it becomes ionic.
23.Which statement describes what happens to a chlorine atom when it forms a chloride ion?
Medium
- AIt loses one electron.
- BIt gains one electron.
- CIt loses one proton.
- DIt gains one proton.
24.What is the formula of the ionic compound formed between calcium and oxygen?
Easy
- ACaO
- BCaO2
- CCa2O
- DCa2O3
25.A student tests the electrical conductivity of an ionic compound in three states: solid, molten, and dissolved in water. Which row shows the correct results?
Easy
- ASolid: no, Molten: yes, Dissolved: yes
- BSolid: yes, Molten: no, Dissolved: no
- CSolid: no, Molten: no, Dissolved: yes
- DSolid: yes, Molten: yes, Dissolved: no
26.Which of the following dot-and-cross diagrams correctly shows the arrangement of electrons in lithium sulfide?
Medium
- ATwo Li atoms each lose one electron to a S atom, forming Li⁺ and S²⁻, with S showing 8 outer electrons.
- BOne Li atom loses one electron to a S atom, forming Li⁺ and S⁻.
- CTwo Li atoms each gain one electron from a S atom, forming Li⁻ and S²⁺.
- DOne Li atom gains one electron from a S atom, forming Li⁻ and S⁺.
27.The table shows the melting points and electrical conductivities of four substances. Which substance is most likely an ionic compound? Substance Melting point (°C) Conducts electricity when solid Conducts electricity when liquid W 3410 yes yes X 801 no yes Y 3550 no no Z -91 no no
Medium
- AW
- BX
- CY
- DZ
28.A student measures the electrical conductivity of an ionic compound at different temperatures. The results show no conductivity at 25°C, but conductivity increases as temperature rises above the melting point. Which statement explains this?
Medium
- AAt 25°C the ions are fixed in the lattice; when molten, the ions are free to move and carry charge.
- BAt 25°C the ions are free to move; when molten, the ions become fixed.
- CAt 25°C the electrons are delocalised; when molten, the electrons are localised.
- DAt 25°C the compound is covalent; when molten, it becomes ionic.
29.Extended Only: A student analysed an ionic compound and a covalent compound using a melting point apparatus. She found the ionic compound had a much higher melting point than the covalent compound. Which statement explains this observation?
Hard
- AIonic compounds are formed from metals only.
- BIonic compounds are formed from nonmetals and nonmetals.
- CThere are strong electrostatic forces of attraction in ionic compounds.
- DThere are strong intermolecular forces in ionic compounds.
30.Extended Only: The diagram shows the electronic configurations of two atoms. Which dot-and-cross diagram correctly represents the ionic compound formed? (Assume the outer shell electrons only are shown.)
Hard
- AThe metal atom (Group 2) loses two electrons, shown as dots, to the non-metal atom (Group 6), shown as crosses, resulting in a 2+ metal ion and a 2- non-metal ion, each with full outer shells.
- BThe metal atom gains two electrons from the non-metal atom, forming a 2- metal ion and a 2+ non-metal ion.
- CThe metal atom shares two electrons with the non-metal atom, forming a covalent bond.
- DThe metal atom loses one electron to the non-metal atom, forming a 1+ metal ion and a 1- non-metal ion.
31.Which of the following describes the formation of a positive ion?
Easy
- AAn atom gains electrons
- BAn atom loses electrons
- CAn atom gains protons
- DAn atom loses protons
32.Which of the following is the correct definition of an ionic bond?
Easy
- AThe sharing of electrons between atoms
- BThe electrostatic attraction between oppositely charged ions
- CThe attraction between a positive ion and delocalised electrons
- DThe force between molecules
33.Which of the following ions has the same electronic configuration as neon?
Medium
- ANa+
- BCl-
- CMg2+
- DAll of the above
34.An atom of element X has electronic configuration 2,8,2. An atom of element Y has electronic configuration 2,8,7. What is the formula of the ionic compound formed between X and Y?
Medium
- AXY
- BXY2
- CX2Y
- DX2Y3
35.Extended Only: Which of the following statements about the electrical conductivity of ionic compounds is correct?
Hard
- AIonic compounds conduct electricity in solid state because ions are free to move
- BIonic compounds conduct electricity in molten state because ions are free to move
- CIonic compounds do not conduct electricity in any state
- DIonic compounds conduct electricity only when dissolved in water, not when molten
36.Extended Only: Magnesium oxide has a higher melting point than sodium chloride. Which statement explains this?
Hard
- AMagnesium oxide has stronger electrostatic forces because the ions have higher charges
- BSodium chloride has stronger electrostatic forces because the ions are smaller
- CMagnesium oxide has weaker electrostatic forces because the ions are larger
- DSodium chloride has a giant lattice structure while magnesium oxide does not
37.Extended Only: In a dot-and-cross diagram for lithium sulfide (Li2S), which of the following is correct?
Hard
- AEach lithium atom loses one electron and sulfur gains two electrons; lithium ions are shown as Li+ and sulfide ion as S2-
- BEach lithium atom gains one electron and sulfur loses two electrons
- CLithium atoms share electrons with sulfur atoms
- DLithium atoms gain two electrons and sulfur loses two electrons
38.Which of the following pairs of elements is most likely to form an ionic compound?
Medium
- ACarbon and oxygen
- BSodium and chlorine
- CNitrogen and hydrogen
- DSilicon and carbon
39.A student measures the electrical conductivity of an ionic compound at different temperatures. The results show no conductivity at 25°C, but conductivity increases as the temperature rises above 800°C. Which statement explains this observation?
Medium
- AAt 25°C the ions are fixed in the lattice and cannot move; above 800°C the compound melts and ions are free to move.
- BAt 25°C the ions are fixed in the lattice and cannot move; above 800°C the electrons become delocalised.
- CAt 25°C the ions can move freely; above 800°C they become fixed.
- DAt 25°C the compound is a liquid; above 800°C it becomes a gas.
40.The table shows the properties of four substances. Which substance is most likely an ionic compound? | Substance | Melting point (°C) | Boiling point (°C) | Conducts electricity when solid | Conducts electricity when liquid | |-----------|-------------------|-------------------|-------------------------------|--------------------------------| | W | 3410 | 5930 | yes | yes | | X | 801 | 1413 | no | yes | | Y | 3550 | 4830 | no | no | | Z | -91 | 98 | no | no |
Hard
- AW
- BX
- CY
- DZ

Slides

What is an Ion?

An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons.
Atoms gain or lose electrons to obtain a full outer shell (like a noble gas).
Positive ions (cations) form when atoms lose electrons.
Negative ions (anions) form when atoms gain electrons.

What change occurs to an atom when it forms a negative ion?

It loses electrons.
It gains protons.
It gains electrons.
It loses protons.

Ionic Bonding

Ionic compounds form when metal atoms react with non-metal atoms.
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 an ionic bond.

Ionic bonding is the electrostatic attraction between ____ charged ions.

Predicting Ion Charges from Groups

Group 1 elements form 1+ ions (e.g., Na⁺).
Group 2 elements form 2+ ions (e.g., Mg²⁺).
Group 6 elements form 2− ions (e.g., O²⁻).
Group 7 elements form 1− ions (e.g., Cl⁻).

Which element does not form a stable ion with the same electronic configuration as neon?

Magnesium
Fluorine
Sodium
Chlorine

Dot-and-Cross Diagrams

Dot-and-cross diagrams show outer-shell electrons only.
Electrons from one atom are shown as dots, the other as crosses.
Square brackets enclose each ion, with the charge written at the top right.
Example: NaCl – Na loses one electron to Cl, forming Na⁺ and Cl⁻.

Which of these are true about dot-and-cross diagrams?

They show all electrons in the atom.
Only outer-shell electrons are usually shown.
The charge is written inside the brackets.
Brackets and charge are shown for each ion.

Ionic Lattice Structure (Extended)

Ionic compounds have a giant lattice structure.
The lattice consists of a regular, repeating arrangement of alternating positive and negative ions.
Strong electrostatic forces act in all directions between oppositely charged ions.

Which statement about an ionic lattice structure is not true?

There is a regular arrangement of ions in the lattice.
The layers of ions slide over each other easily in the lattice.
The ions are arranged with alternating anions and cations.
Strong electrostatic forces of attraction occur between oppositely charged ions.

Properties of Ionic Compounds

Solid at room temperature.
High melting and boiling points.
Conduct electricity when molten or in aqueous solution, but not when solid.
The greater the charge on the ions, the stronger the forces and the higher the melting point.

Ionic compounds conduct electricity when molten because the ions are free to ____.

Why Ionic Compounds Have High Melting Points

They have giant structures with strong electrostatic forces between oppositely charged ions.
These forces require a lot of energy to overcome.
Example: MgO (Mg²⁺ and O²⁻) has a higher melting point than NaCl (Na⁺ and Cl⁻) because of higher charges.

Which statement explains why ionic compounds have high melting points?

They are formed from metals only.
They are formed from non-metals and non-metals.
There are strong electrostatic forces of attraction in ionic compounds.
There are strong intermolecular forces in ionic compounds.

Conductivity of Ionic Compounds

Solid: ions are fixed in the lattice and cannot move → no conduction.
Molten or dissolved: ions are free to move → conduct electricity.

Which of these are correct about sodium chloride?

Sodium chloride has a low melting point.
Sodium chloride conducts electricity in aqueous solution because ions are free to move.
Sodium chloride conducts electricity when solid because ions can carry current through the lattice.

Formation of Magnesium Oxide (Extended)

Mg (Group 2) loses 2 electrons to form Mg²⁺.
O (Group 6) gains 2 electrons to form O²⁻.
The formula is MgO (charges cancel: 2+ and 2−).
Dot-and-cross diagram shows transfer of two electrons.

Magnesium and chlorine react to form MgCl₂. Which row is correct for the electron change and formula of the magnesium ion?

Mg loses 2 electrons, Mg²⁺
Mg gains 2 electrons, Mg²⁺
Mg loses 1 electron, Mg⁺
Mg gains 1 electron, Mg⁺

Summary: Ions & Ionic Bonds

Ions form by electron loss/gain to achieve full outer shells.
Ionic bonds are electrostatic attractions between oppositely charged ions.
Ionic compounds have giant lattices, high melting points, and conduct when molten/dissolved.

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