The Bonding Workshop

One question, three answers

Most people learn three definitions here and can still not say which bonding a given substance has. The definitions are not the problem. The problem is that they are usually taught as three unrelated things, when in fact they are all the same atoms doing the same thing for the same reason. Every atom in this topic wants one thing: a full outer shell of electrons. All three kinds of bonding are ways of getting there, and the only thing that differs between them is who ends up owning the outer electrons. That gives you a test you can apply before measuring anything at all. Is a metal meeting a non-metal, are two non-metals meeting each other, or is a metal on its own? Answer that and the bonding names itself. What the resulting structure then does, how hard it is or what it melts at, is a separate question and a separate module on this topic.

Five words, and what each one is really saying

Read each of these as a description of where the electrons have gone. That is the only thing any of them is about.

Watch the electrons change hands

A piece of sodium is dropped into chlorine gas. Put what happens to the electrons into order.

• A sodium atom has one electron in its outer shell; a chlorine atom is one short of a full one
• The sodium atom hands that outer electron over to the chlorine atom
• Both now have a full outer shell, which is what each of them needed
• The sodium is left positive and the chlorine is left negative, because the electron count no longer matches the proton count
• The opposite charges attract one another strongly, in every direction at once
• Enormous numbers of them pack into a regular giant arrangement rather than staying in pairs

Two unlabelled jars

Two solids sit on a bench. The first is a compound of potassium and bromine. The second is a single element, nickel. Nothing else is known about either. What bonding does each have, and how can you tell?

• The first is ionic and the second metallic, because potassium and nickel are both metals while bromine is not, and what settles it is whether a metal is meeting a non-metal or only other metals
• Both are ionic, because both contain a metal
• The first is covalent and the second ionic, because two different elements always share and a single element always transfers
• Neither can be worked out without first measuring how well each one conducts electricity

The same four questions, three times over

Ask every kind of bonding the same four things and the differences stop being a list to memorise and start being consequences of one decision.

Five bench jars, five different reasons

Balance the charges

An ionic compound carries no overall charge, so the total positive charge must exactly cancel the total negative charge. Aluminium forms ions carrying three positive charges each, and oxygen forms ions carrying two negative charges each. How many oxide ions are needed to balance 10 aluminium ions?

Two sentences to strike out

Five statements from a set of revision notes. Tap the TWO that are wrong.

• In ionic bonding electrons are transferred rather than shared
• A covalent bond is a pair of electrons shared between two atoms
• In metallic bonding the metal atoms are left negatively charged
• A noble gas bonds covalently with itself because its outer shell is already full
• An ionic compound is a giant lattice rather than a collection of separate molecules

States, and the letters after every formula

The same substance can be solid, liquid or gas, and nothing about its bonding changes when it moves between them. What changes is how tightly the particles are held against each other: fixed in place in a solid, touching but free to move past one another in a liquid, far apart in a gas. This matters for one thing in particular. Melting and boiling overcome the forces holding particles together. They do not break the bonds inside a molecule. Working out what temperature that happens at is a question about structure, and the other module on this topic is the one that answers it. What you need here is the notation. Every formula in a balanced equation carries a state symbol: s for solid, l for a pure liquid, g for gas, and aq for a substance dissolved in water. The last two are the ones that cost marks, because dissolved is not the same as melted.

Name the bonding, five in a row

Each description or pairing points to one answer. Three lives.

Three reading groups and one problem

Three reading groups in one town, each facing the same question: who ends up holding the books. In the first group, one member has a spare copy she will never open and another has none and badly wants one. She hands it over for good. From that moment one of them is a person with a book and the other is a person who owes a favour, and that difference between them is exactly what keeps them in touch. Neither is neutral any more. The second group has two people who both want the same single copy and neither will part with it, so they read it together, at the same table, at the same time. Nothing changes hands and nobody ends up owing anybody anything. What holds those two together is the thing they are both holding. The third group does something else entirely. Everybody drops their copies into one pile in the middle of the room, and from then on nobody owns any particular book. Anyone can pick up anything and put it down anywhere. That pile belongs to the whole room rather than to any person in it, which is what keeps the group together and also what makes it so easy for anything to move about.

Put the proper words back

When a metal meets a non-metal the metal hands its outer electrons over. Both atoms end up charged, and a charged atom is called an _____. The attraction between those opposite charges is an _____ bond, and huge numbers of them pack into a giant regular arrangement called a _____. When two non-metals meet, neither will give anything up, so they share a pair of electrons instead, which is a _____ bond. In a metal on its own the outer electrons are released into a pool belonging to the whole piece, where they are described as _____, and the attraction between that pool and the positive ions is a _____ bond.

The letters that cost marks

State symbols are written after each formula in a balanced equation. Select every statement that is correct.

• The symbol s means the substance is present as a solid
• The symbol aq means the substance is dissolved in water
• The symbol l is used for a pure liquid, not for something dissolved in water
• The symbol g means the substance is a gas, and also tells you it is an element
• Anything written aq could equally be written l, since both describe something runny

Four jars on a technician bench

Four jars, each labelled only with what is inside. Decide the bonding in each, and why.

• The first jar is labelled as a compound of potassium and iodine, and nothing else. Decide what is holding it together.
• The second jar holds a compound of nitrogen and hydrogen only. Decide what is holding that one together.
• The third jar holds a single element, zinc, as one solid lump. Decide what is holding the lump together.
• The last jar holds argon. Like the zinc, it is a single element and nothing else. Decide what is holding it together.

Build the answer an examiner wants

Assemble the sentence that gets the marks when a question asks you to explain the bonding in a substance.

Explain all three, from the electrons out

Explain the three kinds of bonding, saying in each case what happens to the outer electrons and what is left holding the substance together. Do not write about melting points or conductivity: this answer is about the bonding itself.

• Say what all three have in common, in terms of what every atom is trying to achieve
• Explain ionic bonding, saying what is transferred and what is left attracting what
• Explain covalent bonding, saying what is shared and why nothing ends up charged
• Explain metallic bonding, saying what is released and what the atoms left behind become
• Finish by explaining how you can tell which of the three a substance has, using only the elements it is made from