Chemical Bonding and Structure

Why atoms join up

Atoms bond because it makes them more stable, and the WAY they bond decides almost everything about the substance that forms. There are three types of bonding to know. - Ionic bonding happens between a metal and a non-metal. The metal gives electrons away and the non-metal takes them, so both become charged particles called ions, and the opposite charges pull together. - Covalent bonding happens between non-metals, which share pairs of electrons instead. - Metallic bonding holds a metal together as a lattice of positive ions in a shared sea of loose, delocalised electrons. The big idea of this unit is that STRUCTURE decides PROPERTIES. Once you know how a substance is bonded and built, you can predict whether it melts easily, whether it conducts electricity, and whether it is hard or soft. This module works through each type and its properties.

Words for bonding

Five terms you need before you use them. Learn what each one means.

Match the bonding or structure to its description

Ionic against simple molecular

Two very common kinds of substance behave in almost opposite ways, and the reason is their structure.

Explain the property

Graphite is a form of carbon that can conduct electricity, which is unusual for a non-metal. Why can it conduct?

• It has delocalised electrons that are free to move and carry charge
• It is made of ions that move even when solid
• It is secretly a metal
• Because it is soft and slippery

Spot the true bonding facts

Tap the TWO statements that are true.

• Ionic bonding forms between a metal and a non-metal
• Metals conduct electricity because of their delocalised electrons
• Covalent bonding works by transferring electrons from one atom to another
• Simple molecular substances have very high melting points

Predict properties from structure

You do not have to memorise the properties of every substance. If you know how it is bonded and built, you can work them out. Ask what holds it together, and how strongly. Giant structures, whether ionic, covalent or metallic, have strong bonds throughout, so they need a lot of heat to melt. Simple molecular substances only have weak forces BETWEEN their molecules, so they melt easily. Ask whether any charged particle is free to move. If charges can move, the substance conducts. That is why molten or dissolved ionic compounds conduct, why metals and graphite conduct through free electrons, and why most simple molecular substances do not conduct at all. ⚠️ Two questions, structure first, then movement of charge, will explain almost any property you are given.

Why metals behave as they do

Select the TWO properties of metals that their delocalised electrons help to explain.

• They conduct electricity
• They can be bent and shaped without shattering
• They all melt at very low temperatures
• They are usually gases at room temperature

Order how an ionic bond forms

Put the steps of forming an ionic bond between a metal and a non-metal in order.

• A metal atom loses one or more electrons
• The metal atom becomes a positive ion
• A non-metal atom gains those electrons and becomes a negative ion
• The oppositely charged ions attract one another
• Many ions build up into a giant lattice

One element, two materials

Here is a worked example that shows how structure decides properties. Diamond and graphite are both made of nothing but carbon, yet they could hardly be more different. Diamond: every carbon atom is joined to four others in a rigid, three-dimensional network. There are no free electrons and nothing can slide, so diamond is extremely hard and does not conduct electricity. Graphite: every carbon atom is joined to only three others, forming flat layers. The layers are held to each other only weakly, so they slide, which makes graphite soft and slippery. Each atom also has one loose electron free to move, so graphite conducts electricity. Same element, different arrangement, opposite properties. That is the whole idea of this unit in a single example.

Complete the bonding facts

A bond made by transferring electrons from a metal to a non-metal is _____ bonding. A bond made by sharing electrons between non-metals is _____ bonding. Metals conduct electricity because they have _____ electrons that are free to move. A charged particle formed when an atom loses or gains electrons is an _____.

Build the bonding rule

Choose the words that complete this statement about ionic compounds.

The bonding run

Five questions on bonding and structure. Three lives.

Explain the substance

Read each case and choose the best answer, then think about why.

• A white solid has a very high melting point and conducts electricity only when it is melted or dissolved in water. What kind of substance is it most likely to be?
• A substance is a gas at room temperature and does not conduct electricity. What does this suggest about its structure?
• You are asked why copper is used for electrical wiring. What is the best explanation?

Explain bonding and structure

A student in the year below cannot see why different substances behave so differently. Explain bonding and structure using what this module has covered.

• Explain the difference between ionic, covalent and metallic bonding
• Explain why an ionic compound conducts electricity only when molten or dissolved
• Explain why simple molecular substances have low melting points
• Explain why metals conduct electricity and can be bent into shape
• Finish by explaining how diamond and graphite can be so different when both are carbon