When you look at a piece of glass, you might not realise that it's made up of two main components: silicon dioxide and sodium oxide. These are just two examples of what we call "period 3 oxides." These oxides are created when a period 3 element reacts with oxygen. But what exactly are period 3 oxides, and why are they so important in the world of inorganic chemistry? In this article, we'll explore the science behind these compounds. First, we'll take a closer look at how period 3 oxides bond together. Then, we'll examine some of their unique properties, like melting point and electrical conductivity. We'll also delve into their acid-base behavior and how they react with water, acids, and bases. Finally, we'll broaden our scope to include other period 3 compounds, like hydroxides and chlorides. By the end of this article, you'll have a better understanding of the fascinating world of period 3 oxides and their role in inorganic chemistry. So let's dive in!

Bonding in period 3 oxides

Let's start by understanding how period 3 oxides bond together. We will focus on seven specific oxides: Na2O, MgO, Al2O3, SiO2, P4O10, SO2, and SO3. We can group them into two categories: metal oxides (Na2O, MgO, and Al2O3) and non-metal oxides (SiO2, P4O10, SO2, and SO3). If you're curious about how these oxides are made, check out our article on 'Period 3 Elements' for more information.

As we move from left to right across the period, the bonding in period 3 oxides changes from ionic to covalent. This is because of the electronegativity difference between the period 3 element and oxygen.

Metal oxides

Na2O and MgO are considered ionic compounds because of the significant difference in electronegativity between the metal and oxygen. They are composed of a lattice structure with alternating positive metal ions and negative oxygen ions.

Al2O3 is also an ionic compound but has a covalent character. Although the electronegativity difference between aluminium and oxygen is large enough to create an ionic bond, the small size and high charge density of the aluminium ion allow it to attract one of the oxygen ion's electron pairs. This changes the electron cloud around the oxygen ion, and the electron pair starts behaving like a shared pair of electrons.

Non-metal oxides

SiO2 is a giant covalent macromolecule. The electronegativity difference between silicon and oxygen isn’t 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.

‍

The properties of period 3 oxides

Melting point of period 3 oxides

The period 3 metal oxides, such as Na2O, MgO, and Al2O3, have high melting points due to their ionic nature. These compounds are held together by strong electrostatic forces between their positive metal ions and negative oxygen ions. MgO and Al2O3 have higher melting points than Na2O because they contain metal ions with higher charges.

On the other hand, SiO2 has an extremely high melting point because it is a giant covalent macromolecule. It is composed of a lattice of silicon and oxygen atoms held together by strong covalent bonds, which require a lot of energy to break. Simple covalent oxides like P4O10, SO2, and SO3 have low melting points because they are made up of weak intermolecular forces that do not 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 its larger size. For more information on this topic, check out our article on "Physical Properties of Bonding".

Electrical conductivity

In their solid state, period 3 oxides cannot conduct electricity. However, their ability to conduct electricity changes in other states.

Metal oxides like Na2O, MgO, and Al2O3 can conduct electricity when molten or in aqueous solution. This is because they are made up of an ionic lattice of positive metal ions and negative oxygen ions. As a solid, the ions are held firmly in place by strong electrostatic forces, and there are no charged particles free to move about. However, when molten or dissolved in water, some of the electrostatic attraction is overcome, and the ions can move around and carry a charge. Non-metal oxides like SiO2, P4O10, SO2, and SO3 cannot conduct electricity in any state since they do not contain any charged particles that can carry a charge. When it comes to oxidation states, oxygen always takes the lower oxidation state in period 3 oxides since it is more electronegative than all of the elements in the period. In particular, it always takes an oxidation state of -2. By using this knowledge, we can determine the oxidation states of the other elements involved in the compound. The sum of the oxidation states in a neutral compound is always zero. Here is a table to help understand this concept:

‍

‍

Period 3 oxides, which all contain oxygen, react differently with oxygen, acids, and bases depending on their acid-base nature. In general, metal oxides on the left side of period 3 are basic, while non-metal oxides are acidic. Al2O3 is amphoteric, meaning it can act as both an acid and a base.

Period 3 metal oxides, such as Na2O and MgO, are basic in nature and react with water to produce a hydroxide, forming a basic solution. Na2O reacts with water to form NaOH, while MgO reacts with water to form Mg(OH)2. On the other hand, period 3 non-metal oxides like P4O10, SO2, and SO3 are acidic in nature and react with water to form an acid. P4O10 reacts with water to form H3PO4, SO2 reacts with water to form H2SO3, and SO3 reacts with water to form H2SO4.

Al2O3 is amphoteric and can react as both an acid and a base. However, it is insoluble in water and won't react with it. SiO2 is also insoluble in water and won't react with it either. It's important to not confuse the different sulfur-containing acids that can be formed, such as H2SO3 (sulphurous acid) and H2SO4 (sulphuric acid).

‍

‍

Period 3 oxides' reactions with acids and bases depend on their acid-base nature. Metal oxides like Na2O and MgO are basic and react with acids to form a salt and water. For example, Na2O reacts with HCl to produce NaCl and H2O, while MgO reacts with HCl to produce MgCl2 and H2O. Al2O3 is amphoteric and can behave as both an acid and a base. It reacts with acids to form a salt and water, like the other metal oxides, but it can also act as an acid by reacting with bases to form an aluminate.

Non-metal oxides like SiO2, P4O10, SO2, and SO3 are acidic and react with bases to form a salt and water. For example, SiO2 reacts with NaOH to produce NaSiO3 and H2O, while P4O10 reacts with NaOH to produce a mixture of salts including Na3PO4 and H2O. SO2 reacts with NaOH to produce Na2SO3 and H2O, while SO3 reacts with NaOH to produce Na2SO4 and H2O.

It's important to note that the reactions between period 3 oxides and acids or bases depend on the nature of the oxide and the type of acid or base involved. Understanding the acid-base nature of these compounds can help predict the products of their reactions. 

Summary of reactions of period 3 oxides

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

‍

Period 3 hydroxides

Another type of period 3 compound that you might need to know about is period 3 hydroxides. In this section, we’ll 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

NaCl and MgCl2 are the two period 3 chlorides. They have high melting points due to their strong ionic bonding. NaCl has a melting point of 801°C, while MgCl2 has a melting point of 714°C.

Both NaCl and MgCl2 have a +2 oxidation state for the chlorine atom. This is because they are both ionic compounds and the chlorine atom gains two electrons to form a stable octet. When period 3 chlorides are added to water, they dissolve and dissociate into their respective ions. NaCl dissociates into Na+ and Cl- ions, while MgCl2 dissociates into Mg2+ and 2Cl- ions. These ions are free to move around in the solution and carry an electrical charge, making the solution conductive. Overall, understanding the properties of period 3 chlorides, including their high melting points, oxidation states, and behavior in water, can help us better understand their chemical reactivity and potential uses in various applications.

Melting point

Understanding the melting points of period 3 chlorides can help us predict their behavior in different applications. Ionic metal chlorides like NaCl and MgCl2 are useful in industries such as metallurgy, where their high melting points make them ideal for high-temperature applications. In contrast, covalent non-metal chlorides like SiCl4 and PCl5 are useful as reagents in organic chemistry reactions, where their low melting points and ability to form covalent bonds make them ideal for certain reactions.

AlCl3 is an interesting case, as it can behave as both an ionic and a covalent compound depending on the temperature and pressure. This property is useful in certain chemical reactions, where the ability to switch between ionic and covalent bonding can affect reactivity and product formation. Overall, the melting points of period 3 chlorides reflect their bonding nature and can be used to predict their behavior in different applications.

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 element’s group number.

This is supported by the Chemistry LibreTexts article "Oxidation States of Transition Metals" which states that "Scandium is one of the two elements in the first transition metal period which has only one oxidation state (zinc is the other, with an oxidation state of +2). All the other elements have at least two different oxidation states.

The StudySmarter article "Period 3 Elements: Properties & Trends" also supports this statement, noting that "Period 3 Elements Chemical Analysis Formulations Instrumental Analysis Pure Substances Sodium Hydroxide Test Test for Anions Test for Metal Ions Testing for Gases Testing for Ions Chemical Reactions Acid-Base Reactions Acid-Base Titration Bond Energy Calculations Decomposition Reaction Displacement Reactions Electrolysis of Aqueous Solutions.

Finally, the ThoughtCo article "Periodic Table of the Elements - Oxidation Numbers" states that "the oxidation number refers to the electrical charge of an atom. Typically, this relates to the number of electrons that must be gained (negative oxidation number) or lost (positive oxidation number) for the atom's valence electron shell to be filled or half-filled. However, most metals are capable of multiple oxidation states.

‍

Reaction with water

Understanding the reactions of period 3 chlorides with water can help us predict their behavior in different applications. Ionic metal chlorides like NaCl and MgCl2 dissolve in water, forming neutral or slightly acidic solutions depending on the metal ion. These properties are useful in industries such as food and pharmaceuticals, where the neutral or slightly acidic pH of the solutions can be important for product stability. In contrast, covalent non-metal chlorides like AlCl3 and SiCl4 react more vigorously with water, forming acidic solutions with low pH values. These properties are useful in industries such as chemical synthesis, where the acidic nature of the solutions can affect reaction rates and product formation. Overall, the reactions of period 3 chlorides with water reflect their bonding nature and can be used to predict their behavior in different applications.

Period 3 oxides are an important class of compounds that have a variety of industrial and scientific applications. Understanding their properties and behavior can help predict their usefulness in different contexts. One key takeaway is that the bonding in period 3 oxides changes from ionic to covalent as you move across the period. This has important implications for their melting points, basic/acidic nature, and reactivity with water. For example, metal oxides tend to be ionic and basic in nature, while non-metal oxides tend to be covalent and acidic. Another important takeaway is that there are exceptions to these trends, such as the amphoteric behavior of Al2O3 and Al(OH)3, and the low melting point of AlCl3. These exceptions highlight the importance of carefully considering the properties of each individual compound. Overall, understanding the properties and behavior of period 3 oxides can inform decisions in various fields, from materials science to chemical synthesis.

Period 3 Oxides

Which is the most basic oxide in period 3?

Na2O is the most basic oxide in period 3.

Which element in period 3 is amphoteric?

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

How do period 3 oxides react with water?

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.

What are oxides?

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

What are the characteristics of period 3 oxides?

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.

‍