Dots-And-Cross Diagrams

Dot-and-Cross Diagrams

Dot-and-cross diagrams can show electrons being transferred and ions being formed. Dots represent electrons from 1 atom and crosses represent electrons from the other atom. Square brackets and a charge (e.g. 2+) represent ions.

How is sodium fluoride formed?

The sodium atom transfers its outer electron to the fluorine atom, creating Na⁺ and F^- ions. Both of these ions have full outer shells.

How is calcium oxide formed?

The calcium atom transfers its 2 outer electrons to the oxygen atom, creating Ca²⁺ and O^2- ions which both have full outer shells.

Dot-and-Cross Diagrams

Dot-and-cross diagrams can be used to represent covalent bonds and to show the sharing of electron pairs.

Illustrative background for Chlorine (Cl<sub>2</sub>)

Illustrative background for Chlorine (Cl<sub>2</sub>) ?? "content

Chlorine (Cl₂)

Each chlorine (Cl) atom begins with 7 electrons in its outer shell.
By sharing 1 pair of electrons in a single covalent bond, each Cl atom obtains a full outer shell with 8 electrons.

Illustrative background for Water (H<sub>2</sub>O)

Illustrative background for Water (H<sub>2</sub>O) ?? "content

Water (H₂O)

Because oxygen has 6 electrons in its outer shell, it needs to have 2 extra electrons shared with it to get a full outer electron shell.
To do this, it forms a single covalent bond with 2 hydrogen atoms.

Double and triple bonds

The earlier examples show single covalent bonds (1 shared pair of electrons between atoms), but it is also possible to form double (2 shared pairs) and even triple covalent bonds (3 shared pairs).
Double and triple bonds are normally stronger and require more energy to break.

Illustrative background for Oxygen (O<sub>2</sub>)

Illustrative background for Oxygen (O<sub>2</sub>) ?? "content

Oxygen (O₂)

Each oxygen needs 2 electrons to get a full outer shell.
So, each oxygen atom shares 2 electrons with the other, leaving 2 pairs of electrons in the shared space between the atoms.
This is an example of a double covalent bond.

1Atomic Structure

2Chemical Bonding

2.1Chemical Bonds

2.1.1Types of Bonds

2.1.2Ionic Bonds

2.1.3Ionic Compounds

2.1.4Covalent & Metallic Bonds

2.1.5Representing Covalent Bonds

2.1.6Dots-And-Cross Diagrams

2.1.7Exam-Style Questions - Chemical Bonds

2.2States of Matter

2.2.1States of Matter

2.2.2Changing State

2.2.3Changing State HyperLearning

2.2.4State Symbols

2.2.5Exam-Style Questions - States of Matter

2.3Chemical Properties

2.3.1Chemical Properties of Ionic Compounds

2.3.2Chemical Properties of Small Molecules

2.3.3Molecular Forces & Polymers

2.3.4Metals & Giant Covalent Structures

2.3.5Alloys & Conductors

2.3.6Carbon Structures - Diamond & Graphite

2.3.7Carbon Structures - Graphene & Fullerenes

2.3.8Carbon Structures - Summary

2.3.9Nanoparticles

2.3.10Nanotechnology

2.3.11Surface Area to Volume Ratio & Nanotechnology Uses

2.3.12End of Topic Test - Chemical Bonding

2.3.13Grade 9 - Bonding & Structure

2.3.14Exam-Style Questions - Allotropes of Carbon

3Quantitative Chemistry

4Chemical Changes

5Energy Changes

5.1Exothermic & Endothermic Reactions

5.1.1Energy Conservation

5.1.2Exothermic & Endothermic Reactions

5.1.3Reaction Profiles

5.1.4Reaction Profiles 2

5.2Chemical Cells & Fuel Cells

5.2.1Chemical Cells

5.2.2Batteries & Charging of Cells

5.2.3Fuel Cells

5.2.4Hydrogen Fuel Cell

5.2.5End of Topic Test - Energy Changes

5.2.6Grade 9 - Energy Changes

5.2.7Exam-Style Questions - Fuel Cells

6The Rate & Extent of Chemical Change

6.1Rate of Reaction

6.1.1Chemical Reactions

6.1.2Collision Theory

6.1.3Catalysts

6.1.4Catalysts in Industry

6.2Reversible Reactions

6.2.1Reversible Reactions

6.2.2Equilibrium

6.2.3Equilibrium Position

6.2.4Equilibrium Position 2

6.2.5End of Topic Test - Rates of Reaction

6.2.6Grade 9 - Rate & Extent of Chemical Change

6.2.7Exam-Style Questions - Reversible Reactions

7Organic Chemistry

8Chemical Analysis

8.1Purity, Formulations & Chromatography

8.1.1Purity & Formulations

8.1.2Chromatography

8.1.3Paper Chromatography 1

8.1.4Paper Chromatography 2

8.1.5Required Practical - Paper Chromatography

8.2Identification of Common Gases

8.2.1Identification of Hydrogen & Oxygen

8.2.2Identification of Carbon Dioxide & Chlorine

8.3Identifying Ions

8.3.1Flame Tests

8.3.2Required Practical: Flame Tests

8.3.3Metal Hydroxides

8.3.4Carbonates

8.3.5Halides, Sulfates

8.3.6Methodology for Chemical Analysis

8.3.7Flame Emission Spectroscopy

8.3.8End of Topic Test - Chemical Analysis

8.3.9Grade 9 - Chemical Analysis

8.3.10Exam-Style Questions - Identification of ions

9Chemistry of the Atmosphere

9.1The Earth's Atmosphere

9.1.1Proportions of Gases in the Atmosphere

9.1.2Oxygen & Carbon Dioxide in the Atmosphere

9.1.3Greenhouse Gases & Human Activities

9.1.4Greenhouse Gases & Human Activities

9.1.5Greenhouse Gases & Climate Change

9.1.6Carbon Footprints

9.1.7Common Atmospheric Pollutants & Their Properties

9.1.8End of Topic Test - The Earth

9.1.9Grade 9 - Chemistry of the Atmosphere

9.1.10Exam-Style Questions - Earth's Atmosphere

10Using Resources

10.1Using the Earth's Resources

10.1.1Potable Water & its Sources

10.1.2Potable Water in the UK & in Saudi Arabia

10.1.3Natural Resources

10.1.4Waste Water

10.1.5Metal Ore Extraction & the Properties of Copper

10.1.6Overexploitation & Alternative Extraction Methods

10.2Life Cycle Assessments & Recycling

10.2.1Life Cycle Assessments

10.2.2Difficulties with LCA

10.2.3Reducing Resource Usage

10.2.4Reducing Use of Metal and Glass

10.2.5Exam-Style Questions - Life Cycle Assessments

10.3Using Materials

10.3.1Corrosion

10.3.2Alloys

10.3.3Ceramics

10.3.4Polymers & Composites

10.4The Haber Process & NPK Fertilisers

10.4.1The Haber Process

10.4.2The Haber Process - Equation & Trade-Offs

10.4.3Formulated vs Manure Fertilisers

10.4.4NPK Fertilisers 1

10.4.5NPK Fertilisers 2

10.4.6End of Topic Test - Resources

10.4.7Grade 9 - Using Resources

10.4.8Exam-Style Questions - The Haber Process

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