Ionic Bonding in Edexcel IGCSE Chemistry

chemistry

Ion

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

Anion

Negative ions that form when atoms gain electrons, meaning they have more electrons than protons.

Cation

Positive ions that form when atoms lose electrons, meaning they have more protons than electrons.

Formation of Cations

All metals lose electrons to other atoms to become positively charged ions.

Formation of Anions

All non-metals gain electrons from other atoms to become negatively charged ions.

Charge of an Ion

The number of electrons that an atom gains or loses is the same as the charge.

Common Ions with Positive Charge

Includes Group 1 metals (1+), Group 2 metals (2+), Group 3 metals (3+), Silver (Ag), Copper(II) (Cu), Iron(II) (Fe), Iron(III) (Fe), Lead(II) (Pb), Zinc(II) (Zn), and Hydrogen (H).

Common Ions with Negative Charge

Includes Group 5 non-metals (3-), Group 6 non-metals (2-), Group 7 non-metals (1-), Hydroxide (OH), Carbonate (CO3 2-), Nitrate (NO3 -), and Sulfate (SO4 2-).

Outer Electron Shell

The electrons in the outermost shell of an atom that determine its ability to gain or lose electrons.

Compound Ions

Ions made from more than one element.

Group 1 Metals

Metals that typically form 1+ ions (e.g., Sodium - Na).

Group 2 Metals

Metals that typically form 2+ ions (e.g., Magnesium - Mg).

Group 3 Metals

Metals that typically form 3+ ions (e.g., Aluminum - Al).

Silver Ion

A common ion with a positive charge represented as Ag.

Copper(II) Ion

A common ion with a positive charge represented as Cu 2+.

Iron(II) Ion

A common ion with a positive charge represented as Fe 2+.

Iron(III) Ion

A common ion with a positive charge represented as Fe 3+.

Lead(II) Ion

A common ion with a positive charge represented as Pb 2+.

Zinc(II) Ion

A common ion with a positive charge represented as Zn 2+.

Hydrogen Ion

A common ion with a positive charge represented as H.

Ammonium Ion

A common ion with a positive charge represented as NH4+.

Group 5 Non-metals

Non-metals that typically form 3- ions (e.g., Nitrogen - N).

Group 6 Non-metals

Non-metals that typically form 2- ions (e.g., Oxygen - O).

Group 7 Non-metals

Non-metals that typically form 1- ions (e.g., Chlorine - Cl).

Ionic compounds

Typically have no overall charge.

Charge cancellation

The size of any positively charged ion is cancelled by the size of any negatively charged ion.

Iron(II) ion

Fe, which has a 2+ or +2 charge.

Sulfate ion

SO, which has a 2- or -2 charge.

Formula of iron(II) sulfate

FeSO4.

Swap-and-drop method

A method used when ions have different charges to determine the formula of an ionic compound.

Copper(II) ion

Cu, which has a 2+ or +2 charge.

Chloride ion

Cl, which has a 1- or -1 charge.

Formula of copper(II) chloride

CuCl2.

Worked example of iron chloride

The compound produced from iron wool and chlorine is FeCl3.

Complex ions

Ions such as carbonate, hydroxide, or sulfate that may require brackets in their formula.

Magnesium ion

Forms ions with a 2+ charge.

Hydroxide ion

Has a 1- charge.

Formula of magnesium hydroxide

Mg(OH)2.

Direct comparison method

A method to determine the formula of an ionic compound by comparing the charges of the ions.

Overall charge of ionic compounds

The overall charge is zero when the charges of the ions cancel each other out.

Number of chloride ions in FeCl3

Three chloride ions are needed to cancel the +3 charge on Fe.

Naming ionic compounds

The metal retains its name and the non-metal changes to its corresponding anion name.

Charge of iron ion in FeCl3

The iron ion has a 3+ or +3 charge.

Charge of chloride ion in FeCl3

The chloride ion has a 1- or -1 charge.

Mathematical representation of charge cancellation

Mathematically, (+3) + (-1) ≠ 0.

Ionic Bonds

Ionic bonds can be represented diagrammatically using dot-and-cross diagrams.

Dot-and-Cross Diagrams

The electrons from each atom should be represented by using solid dots and crosses.

Sodium Ion

A positive sodium ion with the charge 1+ is formed when sodium loses one outer electron.

Chloride Ion

A chlorine atom will gain an electron to form a negatively charged chloride ion with a charge of 1-.

Sodium Chloride Formula

The formula of sodium chloride is NaCl.

Magnesium Ion

A positive ion with the charge 2+ is formed when magnesium loses two outer electrons.

Oxygen Ion

Oxygen atom will gain two electrons to form a negative ion with charge 2-.

Magnesium Oxide Formula

The formula of magnesium oxide is MgO.

Ionic Compounds

An ionic compound consists of a regular arrangement of alternating positive and negative ions.

Electrostatic Forces

Strong electrostatic forces of attraction exist between the oppositely charged ions.

Giant Ionic Lattice

Thousands of positive and negative ions in an ionic compound form a giant lattice structure.

Melting Points of Ionic Compounds

Compounds with giant ionic lattices have high melting points.

Conductivity in Solid State

Ionic compounds are poor conductors in the solid state because the ions are in fixed positions.

Conductivity in Molten State

Ionic compounds are good conductors of electricity in the molten state or in solution.

Energy to Overcome Forces

The strong electrostatic forces need lots of energy to overcome them.

Higher Melting Point

The greater the charge on the ions, the stronger the electrostatic forces and the higher the melting point will be.

Common Mistake in Exams

A common mistake is to say that ionic compounds conduct electricity because 'electrons' move, when it should be the ions that can move and carry a charge.

Fixed Positions of Ions

In the solid state, the ions are unable to move and carry a charge.

Movement of Particles

Molten or aqueous particles move and conduct electricity but cannot in the solid state.

Exam Drawing Requirement

For exam purposes, you need only show the outer electrons in dot & cross diagrams.

Groups for Dot & Cross Diagrams

You should be able to draw dot & cross diagrams for combinations of ions from groups 1, 2, 3, 5, 6, and 7.