What is the general trend in metallic character across Period 3?
Metallic character decreases from left to right.
What is the state of sodium at room temperature?
Solid.
What is the state of chlorine at room temperature?
Gas.
What type of oxide is sodium oxide (Na₂O)?
Basic oxide.
What type of oxide is aluminium oxide (Al₂O₃)?
Amphoteric oxide.
What type of oxide is silicon dioxide (SiO₂)?
Acidic oxide.
Does sodium react with water?
Yes, slowly.
Does aluminium react with water?
No, not with cold water.
How does the atomic radius change across Period 3?
It decreases from left to right.
Do metals in Period 3 conduct electricity?
Yes, they are good conductors.
Is silicon a good conductor or a poor conductor of electricity?
It is a semiconductor.
What is the oxidation state of chlorine in most of its compounds?
-1.
What happens to the electronegativity across Period 3?
It increases from left to right.
Is argon reactive?
No, it is unreactive.
Do elements in Period 3 react with oxygen?
Yes, they form oxides.
Explanation Questions
Explain why the elements in Period 3 change from metallic to non-metallic properties from left to right.
As you move from left to right across Period 3, the number of electrons in the outer shell increases, and the nuclear charge increases, making it harder for elements to lose electrons and thus reducing the metallic nature of elements while increasing non-metallic nature. Elements on the left have fewer electrons in their outer shells and easily lose them, characteristic of metallic elements; elements on the right have more electrons in their outer shells and tend to gain electrons, characteristic of non-metallic elements.
Explain why the atomic radius decreases across Period 3.
As you move across Period 3, the number of protons in the nucleus increases, leading to a greater nuclear charge. However, electrons are added to the same shell (third electron shell), so there is no significant increase in shielding. The increased nuclear charge pulls the electrons closer to the nucleus, resulting in a smaller atomic radius.
Explain why sodium oxide (Na₂O) is basic, while silicon dioxide (SiO₂) is acidic.
Sodium oxide (Na₂O) is a basic oxide because sodium is a highly reactive metal that forms ionic compounds with oxygen. When Na₂O dissolves in water, it forms hydroxide ions (OH⁻), making the solution alkaline. Silicon dioxide (SiO₂) is an acidic oxide because silicon is a semi-metal that forms covalent bonds with oxygen. In water, it does not form OH⁻ but reacts with alkalis to give silicate anions.
Explain why aluminium oxide (Al₂O₃) is amphoteric.
Aluminium oxide (Al₂O₃) is amphoteric because it can react with both acids and bases. This is due to the aluminium ion having a moderate charge and size, allowing it to interact with both positively and negatively charged ions. Thus, it can act as a base by reacting with acids to produce a salt and water, and it can act as an acid by reacting with bases to produce a salt and water.
Describe the general trend in electrical conductivity across Period 3.
Electrical conductivity is high in metals like sodium, magnesium, and aluminium, with aluminium being the best conductor. Electrical conductivity decreases across the period, because silicon is a semiconductor and non-metals like phosphorus, sulfur, chlorine, and argon are poor conductors of electricity.
Explain why noble gas argon is unreactive.
Argon is unreactive because it has a full outer shell of electrons (octet), which makes it very stable. It neither readily gains nor loses electrons, so it does not form chemical bonds easily. Therefore, it is inert and does not react with other elements.
Compare the reactions of sodium, magnesium, and aluminium with water.
Sodium reacts vigorously with cold water to form sodium hydroxide and hydrogen gas. Magnesium reacts very slowly with cold water but more readily with steam to form magnesium hydroxide and hydrogen gas. Aluminium does not react with cold water due to the formation of a thin, protective layer of aluminium oxide. It only reacts with steam at very high temperatures, forming aluminium oxide and hydrogen gas.
Describe the trend in electronegativity across Period 3.
Electronegativity increases across Period 3. This is because the nuclear charge increases, and atomic radius decreases, which allows atoms to attract bonding electrons more strongly. Metals on the left have low electronegativity, while non-metals on the right have high electronegativity.
Explain the general trend in the melting points of Period 3 elements.
The melting points of elements in Period 3 generally increase from Na to Si due to stronger metallic or covalent bonding as well as stronger van der Waals forces, and then decrease towards Ar, because noble gases have weak intermolecular forces. The strong metallic bonding in metals require more energy to break, whilst the strong covalent network in silicon requires even more energy. The simple molecular structure of non-metals and noble gases need little energy to change state.
Describe how the oxides of Period 3 elements react with water.
Sodium and magnesium oxides dissolve in water to form alkaline solutions, aluminium oxide doesn't dissolve but reacts with both acids and bases, silicon, phosphorus, sulfur, and chlorine oxides will dissolve in water to form acids. The general trend of the oxides is that they become more acidic as you go from left to right across the period.