Period 3

Question 1

What are the Period 3 elements?

Answer 1

Sodium (Na), magnesium (Mg), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), chlorine (Cl), and argon (Ar).

Question 2

What is the trend in atomic radius across Period 3?

Answer 2

Atomic radius decreases due to increasing nuclear charge pulling electrons closer to the nucleus.

Question 3

What is the trend in first ionization energy across Period 3?

Answer 3

First ionization energy generally increases due to increasing nuclear charge, with small drops between Mg and Al, and P and S.

Question 4

Why is there a drop in first ionization energy between magnesium and aluminum?

Answer 4

Aluminum has a 3p electron, which is in a higher energy orbital and easier to remove than magnesium’s 3s electron.

Question 5

Why is there a drop in first ionization energy between phosphorus and sulfur?

Answer 5

Sulfur has paired 3p electrons, causing electron repulsion, which makes one easier to remove.

Question 6

What is the trend in melting points across Period 3?

Answer 6

Increases from Na to Si due to stronger metallic bonds and Si’s giant covalent structure. Decreases from Si to Ar due to weaker van der Waals forces in molecular structures.

Question 7

What bonding and structure do sodium, magnesium, and aluminum have?

Answer 7

Metallic bonding and giant metallic structures.

Question 8

What bonding and structure does silicon have?

Answer 8

Giant covalent structure with strong covalent bonds.

Question 9

What bonding and structure do phosphorus, sulfur, chlorine, and argon have?

Answer 9

Phosphorus, sulfur, and chlorine: Simple molecular. Argon: Monatomic with weak van der Waals forces.

Question 10

How does sodium oxide (Na2O) act as an acid or a base?

Answer 10

Basic oxide; reacts vigorously with water to form sodium hydroxide:

Na2O + H2O → 2NaOH

Question 11

How does magnesium oxide (MgO) act as an acid or a base?

Answer 11

Basic oxide; reacts slowly with Hal to form magnesium chloride:

MgO + 2HCl → MgCl2 + H2O

Question 12

How does aluminum oxide (Al2O3) act as an acid or a base?

Answer 12

Amphoteric; reacts with acids and bases:

With acid: Al2O3 + 6HCl → 2AlCl3 + 3H2O
With base: Al2O3 + 2NaOH + 3H2O → 2Na[Al(OH)4]

Question 13

How does silicon dioxide (SiO2) act as an acid or a base?

Answer 13

Acidic oxide; reacts with strong bases to form silicates:

SiO2 + 2NaOH → Na2SiO3 + H2O

Question 14

How does phosphorus pentoxide (P4O10) act as an acid or a base?

Answer 14

Acidic oxide; reacts with bases:

12NaOH + P4O10 -> 4Na3PO4 + 6H2O

Question 15

How does sulfur dioxide (SO2) act as an acid or a base?

Answer 15

Acidic oxide; reacts with water to form sulfurous acid and with bases to form sulfites:

SO2 + H2O → H2SO3
SO2 + 2NaOH → Na2SO3 + H2O

Question 16

How does sulfur trioxide (SO3) act as an acid or a base?

Answer 16

Acidic oxide; reacts very vigorously with water to form sulfuric acid:

SO3 + H2O → H2SO4
Also reacts with bases: SO3 + 2NaOH → Na2SO4 + H2O

Question 17

How do chlorine and argon react with water?

Answer 17

Chlorine: Reacts moderately to form hydrochloric acid and chloric(I) acid:

Cl2 + H2O → HCl + HClO
Argon: Does not react because it is inert.

Question 18

What happens when magnesium reacts with steam?

Answer 18

Magnesium reacts vigorously with steam to produce magnesium oxide and hydrogen gas:

Mg + H2O (g) → MgO + H2

Question 19

what is the pH of Na2O

Answer 19

13

Question 20

what is the pH oh MgO

Answer 20

9 (only slightly soluble)

Question 21

what is the pH of Al2O3

Answer 21

7 (insoluble)

Question 22

what is the pH of SiO2

Answer 22

7 (insoluble)

Question 23

what is the pH of SiO2

Answer 23

7 (insoluble)

Question 24

what is the pH of P4O10

Answer 24

2

Question 25

what is the pH of SO3 / SO2

Answer 25

2