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Edexcel IGCSE Chemistry 复习笔记 1.6 4 Ionic Bonds: Dot & Cross Diagrams

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Edexcel IGCSE Chemistry 复习笔记 1.6 4 Ionic Bonds: Dot & Cross Diagrams

Ionic Bonds: Dot & Cross Diagrams

Deducing Dot & Cross Diagrams for Ionic Compounds

Sodium is a group 1 metal so will lose one outer electron to another atom to gain a full outer shell of electrons
A positive sodium ion with the charge 1+ is formed
Chlorine is a group 7 non-metal so will need to gain an electron to have a full outer shell of electrons
One electron will be transferred from the outer shell of the sodium atom to the outer shell of the chlorine atom
A chlorine atom will gain an electron to form a negatively charged chloride ion with a charge of 1-

Formula of ionic compound: NaCl

Sodium chloride ionic bonding

Exam Tip

For exam purposes you need only show the outer electrons in 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.

Magnesium Oxide Dot & Cross Diagram

Magnesium is a group 2 metal so will lose two outer electrons to another atom to have a full outer shell of electrons
A positive ion with the charge 2+ is formed
Oxygen is a group 6 non-metal so will need to gain two electrons to have a full outer shell of electrons
Two electrons will be transferred from the outer shell of the magnesium atom to the outer shell of the oxygen atom
Oxygen atom will gain two electrons to form a negative ion with charge 2-

Formula of ionic compound: MgO

Diagram showing the dot-and-cross diagram of magnesium oxide

Exam Tip

When writing about ions, we use the notation 1-, 2+ etc. to describe the charge of the ion, with the number first followed by the sign (+/-). It is incorrect to write them the other way around as this refers to the oxidation state, not the charge.

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