Period 3 elements

Question 1

Define periodicity

Answer 1

Recurrence of similar properties at regular intervals when the elements are arranged in increasing atomic number. This is the repeating pattern in chemical and physical properties shown by elements as you go across a period.

Question 2

Describe the trend in atomic radii across period 3

Answer 2

It decreases across the period. The number of protons (nuclear charge) and the number of electrons increases but the number of principle quantum shells stays constant, therefore shielding is the same. This means that the F.A. between the nucleus and outer electrons is more.

Question 3

Describe the trend in ionic radii across period 3

Answer 3

Atoms on the left lose a whole layer of electrons and become cations, which are smaller than the original atom, and have less shielding (Mg to Si). Remaining atoms atoms are attracted more strongly as there is the same nuclear charge. Vice versa for the anions (P to Cl)

Question 4

Describe the trend in melting point

Answer 4

From Na to Mg, there is an increase due to the increase in the number of delocalized electrons used for metallic bonding. Si is a semiconductor with a giant covalent structure. Phosphorus has 4 atoms, whereas Sulfur has eight, so V.D.W. are stronger. Cl has 2, Ar has 1.

Question 5

Describe the trend in conductivity

Answer 5

Increases from Na to Al. Then drops from Si to Ar

Question 6

Show the reaction and the observations of the rxn between Na and Oxygen.

Answer 6

4Na + O2 → 2Na2O (Sodium oxide)
2Na + O2 → Na2O2 (sodium peroxide)
Orange yellow flame that gives white products.

Question 7

Show the rxn and observations of the rxn between Mg and oxygen

Answer 7

2Mg + O2 → 2MgO (Magnesium oxide)
Bright white flame to give a white product

Question 8

Al and Oxygen

Answer 8

4Al + 3O2 → 2Al2O3 (Aluminum oxide)
Powder burns to give a white product

Question 9

Silicon and Oxygen (when heated strongly)

Answer 9

Si + O2 → SiO2 (Silicon dioxide)

Question 10

Phosphorus and oxygen

Answer 10

P4 + 3O2 → P4O6 (phosphorus III oxide)
P4 + 5O2 → P4O10 (Phosphorus V oxide in excess Oxygen)
Yellow flame producing clouds of white smoke.

Question 11

Sulfur and oxygen

Answer 11

S + O2 → SO2
Burns with a blue flame producing a colorless gas.

Question 12

Chlorine

Answer 12

Does not react directly

Question 13

Argon

Answer 13

No rxn

Question 14

Sodium and Water

Answer 14

2Na + 2H2O → 2NaOH + H2
pH 14 Solution, colorless, Exothermic

Question 15

Magnesium and Water

Answer 15

Mg + 2H2O → Mg(OH)2 + H2 (with cold water)
Mg + H2O → MgO + H2 (steam)