Periodicity (OCR AS Chemistry A): Exam Questions

The Periodic Table displays the chemical elements, arranged in order of increasing atomic number.  It is made up of groups and periods of elements. 

State and explain the general trend in first ionisation energy across period 2 of the Periodic Table.

The general trend in first ionisation energies stated in part (a) is seen across Period 2 of the Periodic Table. However, boron and one other Period 2 element deviate from this trend.  

Identify this element and explain why it deviates from the general trend. 

State why nitrogen is classed as a p block element and give its full electron configuration. 

Identify the Period 3 element that has the lowest melting point.

Explain your answer with reference to bonding and structure.

All elements have a value for a first ionisation energy. The first ionisation energy for all the elements is found in chemistry data books

i) Define the term first ionisation energy of an element.

ii) Write the equation for the first ionisation energy of aluminium.

The table below shows successive ionisation energies of an element A, found in Period 3 of the Periodic Table.

Table 1

Identify element A.

Explain your answer using data from Table 1.

The graph below in Figure 1 shows some information on the elements of Period 3 of the Periodic Table.

State and explain the trend that this graph shows, including why there are values that deviate from the trend.

Explain why the second ionisation energy of aluminium is a larger value than the first ionisation energy.

The table below shows the melting points and atomic radii of the elements in Period 3, Na to Cl.

1pm = 1 x 10^-12 m

Explain the difference in melting point for the elements Na and Mg.

The boiling point of diamond is 3550 ℃, but for carbon dioxide it is -78.5 ℃. Both are covalent substances.

Explain this difference with reference to structure and bonding.

Sulfur exists as S₈ molecules and chlorine as Cl₂ molecules. Use this information to explain the difference in their melting points.

Like carbon dioxide, graphite is also a covalent substance, but it is a solid at room temperature. Graphite has a melting point of around 3600 °C.

Describe the structure and bonding of graphite and explain why it has such a high melting point.

Graphite is made purely of carbon, a non-metal, yet it conducts electricity. Diamond, which is also made purely of carbon, cannot conduct electricity. 

i) Explain this difference in electrical conductivity between graphite and diamond.

ii) Give one other difference in the properties of graphite and diamond.

Graphite is soft and used as a lubricant, whereas diamond is hard and used in many cutting tools. Both are giant covalent structures. 

Explain this difference with reference to structure and bonding.

Both graphite and lithium are good conductors of electricity and have high boiling points.

Explain these similarities in terms of bonding and structure.

Another property which shows a trend across a period of the Periodic Table is first ionisation energy.

On the axes above, sketch a graph to show the trend in first ionisation energy across Period 2 of the Periodic Table. 

Write an equation for the reaction that occurs when the third ionisation energy of silicon is measured.

Explain why the value of the third ionisation energy of silicon is higher than the value of the second ionisation energy of silicon. 

This question is about the elements in the first four periods of the Periodic Table.

Explain why an oxygen atom is smaller than a nitrogen atom. 

Describe and explain the general trend in first ionisiation energies across Period 3 from Na- Ar. 

Write an equation, including state symbols, to represent the fourth ionisation energy of nitrogen. 

The successive ionisation energies for another element, J, are shown in Table 1. 

Table 1

i) State the formula of the compound when element J reacts with chlorine.

[1]

ii) Explain why the third ionisation energy of element J is larger than the second ionisation energy.

[2]

This question is about the properties and trends of properties of different substances.

Graphite is an allotrope of carbon. 

Table 1 shows some properties of graphite. 

Table 1

i) Describe the bonding and structure in graphite.

[2]

ii) Explain the properties of graphite, shown in the table, in terms of its bonding and structure. 

[3]

Table 2 shows the general trend in melting points across Period 3. 

Table 2

i) Explain why silicon has the highest melting point in Period 3. 

[3]

ii) Explain why sulfur has a higher melting point than phosphorus. 

[3]

Sketch graphs can be used to show trends across a period.

i) Draw a sketch graph to show the general trend in atomic radius across Period 3. 

[1]

ii) Draw a sketch graph to show the general trend in ionisation energy across Period 3. 

[1]

There are two elements which deviate from the general trend in first ionisation energy across period 3.

i) Name these two elements

[1]

ii) For each one, explain why this deviation occurs.

[4]

The bonding and structure of a substance can explain its physical properties. 

The table shows properties of some elements in Period 2 of the Periodic Table. 

Explain these properties in terms of bonding and structure. 

The melting points of Period 2 elements are shown in the table.

Explain the trend in melting point temperatures across the elements of Period 2 in terms of their structure and bonding.

This question is about magnesium.

Magnesium has a second ionisation energy of 1451 kJ mol^-1

i) Write an equation to represent the second ionisation energy of magnesium. 

Include state symbols.

[2]

ii) Explain why strontium has a lower second ionisation energy than magnesium

[3]

Magnesium has a melting point of 650 ^oC.

i) Describe the bonding and structure in magnesium. 

ii) Explain why magnesium has a higher melting point than sodium. 

Magnesium is located in Group 2 of the periodic table. 

i) Give the full electron configuration of the Mg²⁺ ion.

[1]

ii) Suggest whether the Mg²⁺ or Na⁺ ion has a smaller ionic radius.  

Give a reason for your answer. 

[2]

Magnesium has 12 successive ionisation energies. 

On the graph below, add crosses to show the 12 successive ionisation energies of magnesium. The value for the first ionisation energy is already done. 

You do not need to join the crosses. 

This question is about the elements in the Periodic Table.

The early Periodic Table arranged elements in order of increasing atomic mass. 

i) Which two elements from the first twenty elements of the modern Periodic Table are not arranged in order of increasing atomic mass?

[1]

ii) Why does the modern Periodic Table not arrange some elements, like these, in order of increasing atomic mass?

[1]

iii) What is the name of the term used to describe the repeating patterns in the Periodic Table?

[1]

Figure 1  shows the elements from the first three periods of the Periodic Table.

Figure 1

Identify an element that fits each of the following descriptions:

i) An element that forms a 2- ion with the same electronic configuration as Ne 

[1]

ii) The Period 3 element with the highest boiling point 

[1]

iii) The element from the first three periods with the largest atomic radius 

[1]

iv) The element from the first three periods with the highest first ionisation energy

[1]

v) The Period 3 element with the successive ionisation energies shown below: 

[1]

Figure 2 shows the first ionisation energies for six consecutive elements labelled A-F. 

Figure 2

i) Complete the graph to show the first ionisation energies of elements G-K. 

ii) Explain why the value of the first ionisation energy for D is greater than for C.

Diamond is made from the element, carbon.

It has the following properties:

   High melting point

   Poor electrical conductivity

   Hard

Explain these properties of diamond, referring to its structure and bonding.