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Period 3 Oxides

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Period 3 Oxides

Manufactured glass contains about 70% silicon dioxide and 15% sodium oxide. These two oxides are common examples of period 3 oxides, which are made in a reaction between a period 3 element and oxygen.

  • This article is about period 3 oxides in inorganic chemistry.
  • Well start by considering the bonding in period 3 oxides.
  • Well then see how this affects some of their properties, such as the melting point and electrical conductivity, as well as the oxidation state.
  • After that, well look at their reactions with water, acids, and bases. This will involve considering their acid-base behaviour.
  • Finally, well also explore some other period 3 compounds, namely, period 3 hydroxides and chlorides.

Bonding in period 3 oxides

To begin with, lets look at the bonding within period 3 oxides. This will help with our understanding when we investigate the properties and reactions of period 3 oxides later on.

There are many different period 3 oxides, but in this article, we will limit our exploration to just Na2O, MgO, Al2O3, SiO2, P4O10, SO2 and SO3. To make life easier, weve split them into two groups: the metal oxides (Na2O, MgO and Al2O3) and the non-metal oxides (SiO2, P4O10, SO2 and SO3).

If you want to find out how these oxides are made, check out Period 3 Elements for a look at the different reactions.

In general, as you move from left to right across the period, the bonding in period 3 oxides changes from ionic to covalent. This has to do with the electronegativity difference between the period 3 element and oxygen.

Metal oxides

Na2O and MgO are ionic compounds. This is because there is a large electronegativity difference between the metal and oxygen. They consist of a giant lattice of alternating positive metal ions and negative oxygen ions.

Al2O3 is also ionic but displays a covalent character. Although the electronegativity difference between aluminium and oxygen is large enough for a transfer of electrons, forming an ionic bond, the aluminium ion is quite small and has a high charge density. This means that it is partially able to attract one of the oxygen ions pairs of electrons, distorting the oxygen ions electron cloud. The electron pair starts acting a little like a shared pair of electrons.

Non-metal oxides

SiO2 is a giant covalent macromolecule. The electronegativity difference between silicon and oxygen isnt that large, and so SiO2 bonds covalently. It consists of a giant lattice of silicon and oxygen atoms joined by covalent bonds.

P4O10, SO2 and SO3 also bond covalently. However, they form simple covalent molecules instead of a giant covalent macromolecule.

Period 3 Oxides, electronegativity periodic table, StudySmarterElectronegativity in the periodic table. Image credits: commons.wikimedia.org.

The properties of period 3 oxides

Next, lets see how the structure and bonding of period 3 oxides affect their properties. In particular, well focus on the melting point and electrical conductivity. Well also look at the oxidation state.

Melting point of period 3 oxides

The period 3 metal oxides have high melting points, while the simple covalent oxides have low melting points. However, the giant macromolecule SiO2 has a very high melting point.

Metal oxides

Na2O, MgO and Al2O3 have high melting points. This is because they are ionic compounds, held together as a solid by strong electrostatic attraction between their positive metal ions and the negative oxygen ions. MgO and Al2O3 have higher melting points than Na2O because they contain metal ions with a higher charge.

Non-metal oxides

SiO2 has a very high melting point because it is a giant covalent macromolecule. It consists of a lattice of silicon and oxygen atoms stretching in all directions, held together by strong covalent bonds. Melting SiO2 involves overcoming these covalent bonds, which requires a lot of energy.

P4O10, SO2 and SO3 have low melting points. This is because they are simple covalent molecules. Although there are strong covalent bonds within the molecules, the only forces holding the molecules together as a solid are weak intermolecular forces, which dont require much energy to overcome. P4O10 has a higher melting point than SO3, which in turn has a higher melting point than SO2 due to the fact that it is a larger molecule.

Check out Physical Properties of Bonding for more on this topic.

Electrical conductivity

In their solid state, none of the period 3 oxides can conduct electricity. However, this changes in other states.

Metal oxides

Period 3 metal oxides (Na2O, MgO and Al2O3) can conduct electricity when molten or aqueous. Remember that metal oxides are made up of an ionic lattice of positive metal ions and negative oxygen ions. As a solid, these ions are fixed firmly in place by strong electrostatic attraction, and so there are no charged particles free to move about. However, when molten or aqueous, some of the electrostatic attraction is overcome, and the ions are able to move around and carry a charge.

Non-metal oxides

Period 3 non-metal oxides (SiO2, P4O10, SO2 and SO3) cant conduct electricity in any state. This is because they dont contain any charged particles that can carry a charge.

Oxidation state

Now lets have a go at working out the oxidation states of period 3 oxides.

Oxidation states, also known as oxidation numbers, show the number of electrons an element needs to lose or gain compared to its un-combined state.

Earlier in this article, we looked at the relative electronegativities of oxygen and the period 3 elements. Oxygen is more electronegative than all of them. This means that when it comes to period 3 oxides, oxygen always takes the lower oxidation state. In particular, it always takes an oxidation state of -2. The sum of the oxidation states in a neutral compound is always zero, and so using this knowledge, we can work out the oxidation states of the period 3 element involved. This table should help:

Period 3 oxides, oxidation state table, StudySmarterThe oxidation states of period 3 oxides. Anna Brewer, StudySmarter Original

Reactions of period 3 oxides

Period 3 oxides have one thing in common: they all contain oxygen. However, this doesnt mean that they react in the same way. In this next section, well look at how period 3 oxides react with oxygen, acids, and bases. This involves considering their acid-base nature.

An acid is a proton donor, while a base is a proton acceptor.

Head over to Acids and Bases if this is your first time covering these sorts of compounds.

Metal oxides on the left of period 3 tend to be basic in nature, while non-metal oxides are acidic. Al2O3 sits in the middle and is amphoteric.

Period 3 oxide reactions with water

In general, period 3 metal oxides are basic in nature. This means that they react with water to produce a hydroxide, forming a basic solution. On the other hand, period 3 non-metal oxides are acidic in nature. They react with water to form an acid.

Metal oxides

Na2O and MgO react with water to form hydroxides. They do this because of their ionic bonding. They contain strongly basic oxide ions (O2-) thanks to the large electronegativity difference between the metal and oxygen. The oxygen ion can accept a hydrogen ion from the solution, acting as a base.

  • Na2O reacts with water to form NaOH, which dissociates into Na+ and OH- ions.
  • MgO reacts with water to form Mg(OH)2, which is sparingly soluble and partially dissociates into Mg2+ and OH- ions.

Here are the equations:

On the other hand, Al2O3 is insoluble in water and thus wont react at all.

Non-metal oxides

P4O10, SO2 and SO3 react with water to form acids. Because they bond covalently, they dont contain any oxygen ions and so cant act as bases. Instead, theyre able to donate a hydrogen ion in solution, meaning they act as an acid.

  • P4O10 reacts with water to form H3PO4, which partially dissociates into H+ and H2PO4- ions.
  • SO2 reacts with water to form H2SO3 (sulphurous acid), which partially dissociates into H+ and HSO3- ions.
  • SO3 reacts with water to form H2SO4 (sulphuric acid), which fully dissociates into H+ and HSO4- ions.

Youll need to know the equations:

Like Al2O3, SiO2 is insoluble in water. It wont react in water at all.

Dont get your sulphur-containing acids mixed up. Here are the structures of sulphurous acid, H2SO3, and sulphuric acid, H2SO4.

Period 3 oxides, sulphurous sulphuric acid, StudySmarterSulphurous and sulphuric acid. Anna Brewer, StudySmarter Original

Period 3 oxides reaction with acids and bases

We now know that two of the three period 3 metal oxides are basic in nature. They, therefore, react with acids. In contrast, period 3 non-metal oxides are acidic in nature and therefore react with bases. Al2O3 lies between the two groups and is amphoteric in nature.

Metal oxides

Na2O and MgO act as bases by reacting with acids to form a salt and water. This is because they bond ionically. For example:

  • Reacting Na2O with HCl produces NaCl and H2O.
  • Reacting MgO with HCl produces MgCl2 and H2O.

The equations are shown below:

Al2O3 is a little different it is amphoteric. This means that it can behave as both an acid and a base. As with the other period 3 metal oxides, it acts as a base by reacting with an acid to form a salt and water, thanks to its ionic bonding. Here, the aluminium ion has a positive charge. But it can also act as an acid by reacting with bases, thanks to its covalent character. In this case, we form an aluminate, a compound in which the aluminium ion has a negative charge. For example:

  • Reacting Al2O3 with HCl produces AlCl3 and H2O.
  • Reacting Al2O3 with NaOH produces a variety of aluminates, depending on the conditions, one of which could be NaAl(OH)4.

Here are the equations:

Non-metal oxides

SiO2, P4O10, SO2, and SO3 act as acids by reacting with bases to form a salt and water. This is because they bond covalently. For example:

  • Reacting SiO2 with NaOH produces NaSiO3 and H2O.
  • Reacting P4O10 with NaOH is like reacting phosphoric acid with NaOH. It produces a mixture of salts, including Na3PO4, as well as H2O.
  • Reacting SO2 with NaOH is like reacting sulphurous acid with NaOH. Overall, it produces Na2SO3 and H2O.
  • Reacting SO3 with NaOH is like reacting sulphuric acid with NaOH. Overall, it produces Na2SO4 and H2O.

Once again, weve provided you with the equations:

Summary of reactions of period 3 oxides

To round up this section, heres a useful table summarising the reactions of period 3 oxides and their acid-base natures.

Period 3 Oxides, reactions summary table, StudySmarterReactions of period 3 oxides. Anna Brewer, StudySmarter Original

Period 3 hydroxides

Another type of period 3 compound that you might need to know about is period 3 hydroxides. In this section, well look at the reactions of three of the period 3 hydroxides NaOH, Mg(OH)2 and Al(OH)3 with acids and bases.

Check whether period 3 hydroxides are covered by your specification.

Reaction with acids and bases

Both NaOH and Mg(OH)2 act as typical bases. They react with acids to give a salt and water. For example:

  • Reacting NaOH with HCl produces NaCl and H2O.
  • Reacting Mg(OH)2 with HCl produces MgCl2 and H2O.

Here are the equations:

Al(OH)3 behaves a little differently it is amphoteric. It acts as a base, reacting with an acid to produce a salt and water. But it also acts as an acid, reacting with bases to produce an aluminate. For example:

  • Reacting Al(OH)3 with HCl produces AlCl3 and H2O.
  • Reacting Al(OH)3 with NaOH produces NaAl(OH)4.

The equations for these reactions are below:

Period 3 chlorides

The last thing on our agenda today is period 3 chlorides. Well look at their melting points, oxidation number and their reaction with water.

Melting point

In general, the period 3 metal chlorides have high melting points, while the period 3 non-metal chlorides have low melting points. AlCl3 is an anomaly despite being a metal chloride, it has a low melting point.

Metal chlorides

Both NaCl and MgCl2 have high melting points. This is because they are ionic compounds. Thanks to the large difference in electronegativity between the metal and chlorine, theyre able to bond ionically, and the solid is held together by strong electrostatic attraction between the oppositely charged ions.

AlCl3 is a little different. At room temperature and pressure, it bonds ionically, and so youd expect it to have a high melting point. But as you increase the temperature, it turns from an ionic lattice into simple Al2Cl6 molecules, which eventually break up into smaller AlCl3 molecules. These are both examples of simple covalent molecules. Theyre held together as a solid by weak intermolecular forces, which dont require much energy to overcome, and so AlCl3 actually has a low melting point.

Non-metal chlorides

SiCl4, PCl5, SCl2, and S2Cl2 all have low melting points. This is because they are simple covalent molecules. The only forces holding them together as a solid are weak intermolecular forces, which dont require much energy to overcome.

Oxidation state

In all period 3 chlorides, chlorine takes a negative oxidation state of -1. This is because it is more electronegative than the period 3 element it bonds with. The sum of the oxidation states of the atoms in a neutral compound is always zero, and from this, you can work out the oxidation state of the period 3 element. It is quite simple to remember with the exception of SCl2 and S2Cl2, the oxidation state matches the elements group number. The following table summarises the information for you.

Period 3 oxides, oxidation state table chlorides, StudySmarterThe oxidation states of period 3 chlorides. Anna Brewer, StudySmarter Original

Reaction with water

Finally, well explore the reactions of period 3 chlorides with water, including taking a look at the pH of the solution formed. In general, the metal chlorides simply dissolve in water, while the non-metal chlorides react more vigorously. Once again, AlCl3 bucks the trend by reacting like a non-metal chloride.

Metal chlorides

NaCl and MgCl2 both dissolve in water. They do this thanks to their ionic bonding. NaCl forms a neutral solution of Na+ and Cl- ions with a pH of 7, while MgCl2 forms a slightly acidic solution of Mg2+ and Cl- ions with a pH of around 6.

AlCl3 acts differently, thanks to its covalent character. It reacts with water to form an acidic solution with a pH of around 3, giving off steamy fumes of HCl.

Non-metal chlorides

The other non-metal chlorides react much like AlCl3, thanks to their covalent bonding. They react with water to form acidic solutions, each with a pH of around 2. All of the reactions give off steamy fumes of HCl.

There are clear trends in all of the different properties and reactions. Knowing some key facts, such as the type of bonding present in each compound, should help you when it comes to period 3 oxides, hydroxides and chlorides.

Period 3 Oxides - Key takeaways

  • Period 3 oxides are compounds made up of a period 3 element and oxygen.
  • Bonding in period 3 oxides changes from ionic to covalent as you move across the period. The metal oxides tend to be ionic, while the non-metal oxides are covalent. The metal oxide Al2O3 is ionic but shows a covalent character.
  • Period 3 metal oxides tend to have high melting points while the non-metal oxides have low melting points. The non-metal oxide SiO2 is a giant covalent macromolecule and has a very high melting point.
  • Period 3 metal oxides tend to be basic in nature, while period 3 non-metal oxides are acidic. The metal oxide Al2O3 sits in the middle and is amphoteric.
  • Period 3 metal hydroxides tend to be basic in nature. However, the metal hydroxide Al(OH)3 is amphoteric.
  • Period 3 metal chlorides tend to have high melting points while non-metal chlorides have low melting points. The metal chloride AlCl3 is an anomaly and has a low melting point.
  • Period 3 metal chlorides tend to dissolve in water while the non-metal chlorides react more vigorously. The metal chloride AlCl3 once again behaves more like a non-metal chloride and reacts vigorously.

Frequently Asked Questions about Period 3 Oxides

Na2O is the most basic oxide in period 3.

Al2O3 is amphoteric. This means that it can act as both an acid and a base.

Period 3 metal oxides react with water to produce a hydroxide, while period 3 non-metal hydroxides react with water to produce an acid. However, the metal oxide Al2O3 and the non-metal oxide SiO2 are both insoluble and don’t react with water.

Oxides are compounds containing an oxygen atom with an oxidation state of -2. Period 3 oxides are oxides involving the elements in period 3.

The characteristics of period 3 oxides vary. The metal oxides tend to have high melting points, can conduct electricity when molten or aqueous, and are basic in nature, although the metal oxide Al2O3 is amphoteric. The non-metal oxides tend to have low boiling points, can’t conduct electricity, and are acidic in nature, although the non-metal oxide SiO2 has a very high melting point.

Final Period 3 Oxides Quiz

Question

Period 3 metal oxides have ____ melting points.

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Answer

High

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Question

True or false? All period 3 non-metal oxides have low melting points.

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Answer

False

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Question

Which of the following oxides bond covalently?

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Answer

Na2O

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Question

Which of the following oxides bond ionically?

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Answer

Na2O

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Question

Which of the period 3 oxides has the highest melting point? Justify your answer.

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Answer

SiO2

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Question

True or false? Period 3 metal oxides can conduct electricity when solid.

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Answer

False

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Question

When can non-metal period 3 oxides conduct electricity?

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Answer

They can't, no matter their state

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Question

What is the oxidation state of oxygen in all period 3 oxides?

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Answer

-2

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Question

Period 3 metal oxides tend to be ____ in nature.

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Answer

Basic

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Question

Period 3 non-metal oxides tend to be ____ in nature.

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Answer

Acidic

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Question

Which of the following react with water to produce a hydroxide?

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Answer

Na2O

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Question

Which of the following are insoluble in water?

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Answer

Al2O3

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Question

True or false? Al2O3 is amphoteric in nature.

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Answer

True

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Question

Which of the following react with water to produce an acid?

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Answer

SO2

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Question

Period 3 metal oxides react with acids to form _____.

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Answer

A salt plus water.

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Question

Period 3 non-metal oxides react with bases to form ____.

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Answer

A salt plus water.

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Question

How do period 3 metal hydroxides react with acids and bases?

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Answer

NaOH and Mg(OH)2 react with acids to form a salt and water. Al(OH)3 also reacts with acids to form a salt and water. However, it also reacts with bases to form an aluminate.

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Question

Give the products when Al2O3 reacts with an acid and with a base.

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Answer

The reaction with an acid produces a salt and water. The reaction with a base produces an aluminate.

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Question

True or false? All period 3 metal chlorides have high melting points.

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Answer

False

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Question

Which of the following is true?

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Answer

Chlorine takes an oxidation state of -1 in all period 3 chlorides.

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Question

How do NaCl and MgCl2 react with water?

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Answer

They dissolve in water. NaCl produces a neutral solution whilst MgCl2 produces a slightly acidic solution with a pH of 6.

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Question

How do the period 3 non-metal chlorides react with water?

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Answer

They react vigorously, giving off fumes of HCl, and produce acidic solutions with a pH of 2.

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Question

How does AlCl3 react with water?

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Answer

It reacts vigorously, giving off fumes of HCl and forming a solution with a pH of about 3.

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