Chapter 10: Periodicity

Question 1

Why does the atomic radii decrease across a period?

Answer 1

The number of electron shells stay the same.

The protons/nuclear charge increases, so the electrostatic force increases and the protons pulls the electrons closer.

Question 2

Which element has the highest melting point in period 3?

Answer 2

Silicon

Question 3

What is the trend of melting points in period three?

Answer 3

Increase in melting point until silicon, then significant decrease after, (with sulfur having a higher melting point then phosphorus)

Question 4

What is the trend of electrical conductivity in period 3?

Answer 4

Decrease electrical conductivity. Last two elements (Cl and Ar) have 0 electrical conductivity.

Question 5

Which element in period 3 has a giant molecular structure?

Answer 5

Silicon, (the rest is giant metallic or simple molecular)

Question 6

What is the formula of a simple molecule of sulphur?

Answer 6

S8

Question 7

What is the formula of a simple molecule of phosphorus?

Answer 7

P4

Question 8

What period 3 chloride doesn’t react with water?

Answer 8

Magnesium

Question 9

Why doesn’t silicon oxide react with water?

Answer 9

Because it has a giant molecular structure

Question 10

What are the conditions needed for silicon to react with oxygen?

Answer 10

Powdered Si and heat strongly

Question 11

What is the flame colour of sodium?

Answer 11

Bright yellow

Question 12

What is the flame colour of magnesium?

Answer 12

Bright white

Question 13

What is aluminum flame colour?

Answer 13

Bright white

Question 14

What is the flame colour of silicon?

Answer 14

Bright white sparkles

Question 15

What is the flame colour of phosphorus?

Answer 15

yellow or white flame

Question 16

What is the flame colour of sulphur?

Answer 16

Blue flame

Question 17

What is the product of sulphur’s reaction with oxygen

Answer 17

sulfur dioxide that is shown as toxic fumes

Question 18

What are the reaction conditions needed for phosphorus?

Answer 18

Heat and excess chlorine

Question 19

Which period three elements react slowly with chlorine?

Answer 19

Silicon and phosphorus.

Question 20

Describe sodium’s reaction with cold water.

Answer 20

It reacts vigorously with cold water.
It melts into a ball, and dissolves completely
hydrogen is given off
strong alkaline solution (PH14) formed.

Question 21

Describe magnesium’s reaction with cold water and hot.

Answer 21

It reacts extremely slowly with cold water, forming PH 11 solution, since magnesium hydroxide is only slightly soluble. But it reacts vigorously with steam.

Question 22

Which oxides are insoluble in water?

Answer 22

Aluminum and silicon

Question 23

What colour of flame is produced when sodium reacts with chlorine?

Answer 23

Bright orange

Question 24

What colour of flame is produced when magnesium reacts with chlorine?

Answer 24

Bright white

Question 25

What is observed when aluminum reacts with chlorine?

Answer 25

Pale yellow aluminum chloride is produced

Question 26

What is the molecular formula of aluminum chloride?

Answer 26

Al2Cl6

Question 27

What is produced when silicon dioxide reacts with sodium hydroxide?

Answer 27

sodium silicate (Na2SiO3) and water

Question 28

What is the product produced when aluminum chloride reacts with water?

Answer 28

[Al(H20)6]3+ and chlorine ions

Question 29

What is observed when chlorine is produced?

Answer 29

Misty fumes

Question 30

Which period 3 chloride can conduct electricity when it is added to water but not when it is in its liquid state?

Answer 30

Phosphorus and silicon