3.2.1 - Periodicity

Question 1

What is periodicity?

Answer 1

The repeating pattern of physical/chemical properties going across the periods.

Question 2

Explain the atomic radius as we go across period 3.

Answer 2

Atomic radii decreases as we go along period 3 due to the increased number of protons, which creates a stronger attraction to the nucleus.

Question 3

What do the first 3 elements have in period 3 (bonding)?

Answer 3

Metallic.

Question 4

Explain the boiling point trend in period 3.

Answer 4

General increase in melting points as we go across period 3 due to increased delocalised electrons and a smaller ionic radius.

Question 5

Why does silicon have the highest boiling point in period 3?

Answer 5

Silicon has macromolecular, giant covalent structures with many strong covalent bonds, requiring more energy to break.

Question 6

Why does phosphorus have a smaller melting point than silicon?

Answer 6

Phosphorus has a weaker simple molecular structure determined by van der Waals forces, which are much weaker.

Question 7

Explain why chlorine and argon have lower melting points.

Answer 7

Chlorine and argon have simple molecular structures with weak intermolecular forces.

Question 8

What is formed when magnesium burns in oxygen?

Answer 8

A bright white flame, producing a white solid.

Question 9

Suggest one property of aluminium oxide that causes aluminium to resist corrosion in water.

Answer 9

It is insoluble.

Question 10

Write an equation for the reaction between aluminium oxide and HCl.

Answer 10

Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O

Question 11

Write an equation for the reaction between aluminium oxide and an excess of aqueous sodium hydroxide.

Answer 11

Al₂O₃ + 2NaOH + 3H₂O → 2NaAl(OH)₄

Question 12

Explain why lithium oxide has a higher melting point than sodium oxide.

Answer 12

Lithium ion is smaller than the sodium ion, attracting the O²⁻ ion more strongly.

Question 13

State the type of bonding in basic oxides and explain why.

Answer 13

Ionic; they contain O²⁻ ions which react with water to form OH⁻ ions.

Question 14

Suggest why silicon dioxide is described as a basic oxide.

Answer 14

It reacts with bases.

Question 15

What happens to periodicity across period 3?

Answer 15

Atomic radius decreases due to an increase in protons, resulting in a stronger attraction to the nucleus.

Question 16

Explain what happens with the ionisation energy between magnesium and aluminium.

Answer 16

Aluminium has a reduced ionisation energy due to increased shielding and being further from the nucleus.

Question 17

What is the trend in electronegativity?

Answer 17

Generally increases across a period and decreases down a group, but usually not for the last element.

Question 18

Why do P₄O₁₀ and SO₂ have low melting points?

Answer 18

They form simple molecular structures with weak intermolecular forces, making the bonds easy to break.

Question 19

Give 4 physical properties of silicon dioxide.

Answer 19

Brittle, non-conductor, hard, insoluble.

Question 20

Write the equation for how sodium reacts with oxygen.

Answer 20

4Na + O₂ → 2Na₂O

Question 21

Write the equation for how magnesium reacts with oxygen.

Answer 21

2Mg + O₂ → 2MgO

Question 22

Write the equation for how aluminium reacts with oxygen.

Answer 22

4Al + 3O₂ → 2Al₂O₃

Question 23

Write the equation for how phosphorus reacts with oxygen.

Answer 23

4P + 5O₂ → P₄O₁₀

Question 24

How are elements classified into s, p, and d blocks on the periodic table?

Answer 24

Elements are classified based on the orbitals in which the highest energy electrons reside.

Question 25

Explain the trend in atomic radii across a period in the periodic table.

Answer 25

Atomic radii decrease from left to right due to increasing nuclear charge pulling electrons closer.

Question 26

Describe the general trend and exceptions in the first ionisation energies across Period 3.

Answer 26

First ionization energies generally increase across a period, with exceptions between Mg and Al, and between P and S.

Question 27

Explain the trend in melting and boiling points across Period 3 from Na to Ar.

Answer 27

Na to Al show increasing melting points due to stronger metallic bonding; Si has a very high melting point due to its macromolecular structure.

Question 28

How are the trends in Period 2 similar to those in Period 3 regarding physical properties?

Answer 28

Both periods show similar trends in atomic radius, ionization energy, and melting points.

Question 29

Why do elements like boron and carbon have much higher melting points compared to their neighbors?

Answer 29

Boron and carbon form macromolecular structures with strong covalent bonds.

Question 30

How do the electron configurations of elements influence their chemical and physical properties?

Answer 30

The electron configuration determines an element’s reactivity, ionization energy, and types of bonds it can form.

Question 31

Define periodicity in the context of the periodic table.

Answer 31

Periodicity refers to the repeating pattern of chemical and physical properties of elements across different periods.

Question 32

Which block does molybdenum belong to in the periodic table?

Answer 32

Molybdenum is classified as a d-block element.

Question 33

Which element in Period 3 has the highest melting point?

Answer 33

Silicon has the highest melting point among the elements in Period 3.

Question 34

Which ion has the largest radius among the given options?

Answer 34

O²⁻ has the largest radius.

Question 35

Which element has a first ionisation energy lower than that of sulfur?

Answer 35

Selenium has a lower first ionisation energy than sulfur.

Question 36

What is the equation for the reaction of phosphorus(V) oxide with water, and suggest a possible pH for the solution?

Answer 36

P₄O₁₀ + 6H₂O → 4H₃PO₄ ## Footnote The solution is likely to be acidic.

Question 37

What is the formula of a hydroxide of an element in Period 3 that is used in medicine?

Answer 37

The formula is Mg(OH)₂, which is magnesium hydroxide.

Question 38

Which element in Period 3 has the largest atomic radius?

Answer 38

Sodium has the largest atomic radius in Period 3.