Periodicity (AQA A Level Chemistry)

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 a period 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. 

Figure 1

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.

Properties of elements in the Periodic Table can be predicted based on the element’s position, and various trends in properties are shown across the periods and down the groups of the Periodic Table. 

State and explain the trend in the atomic radii of the elements seen across Period 3.

Another property which shows a trend across a period of the Periodic Table is the melting point of a substance.

Explain why the melting point of sodium is lower than that of magnesium.

Explain how sodium conducts electricity.

Explain why the melting point of phosphorus (P₄) is lower than the melting point of sulfur (S₈). 

The Periodic Table is constructed in groups and rows of elements, and there are a number of periodic trends which can be seen.

Identify the element, from silicon to chlorine, that has the largest atomic radius.

Explain your answer.

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

Figure 1

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.

The atoms of metal elements from the Periodic Table will lose electrons to form positive metal ions. Different ions have different sizes.

State which of Mg²⁺ and Al³⁺ is the larger ion. Explain your answer.

The following table shows some successive ionisation energies of an element in Period 3 of the Periodic Table. 

Table 1

Identify this Period 3 element and state the equation for the final ionisation energy which will take place. 

Explain how successive ionisation energies demonstrate the existence of electron shells within atoms.

Use Table 1 to fully justify your answer. 

Give the meaning of the term 'periodicity'.

Include in your answer reference to the atomic radii of the Period 2 and Period 3 elements.

Specific values of atomic radii are not required.

Aluminium has 13 successive ionisation energies.

On Figure 1 below, plot the 13 successive ionisation energies of aluminium. The value for the first ionisation energy is already completed.

You do not have to join the crosses.

Figure 1

This question is about ionisation energies.

Figure 2 represents log of the first ten successive ionisation energies of an element X plotted against the number of the electron removed.

Figure 2

State which group in the periodic table element X belongs to.

Element A has the following first six ionisation energies in kJ mol^-1.

577, 1820, 2740, 11 600, 14 800, 18 400

i) Explain how you know that element A is in group 3 of the periodic table.

ii) Two elements B and C are in the same period as A, but B is in the group before A and C is in the group after A in the periodic table. Give approximate first ionisation energies for elements B and C.

iii) Explain, using ideas of electronic structure, the difference in ionisation energy values of element A compared to elements B and C.

This question refers to the elements in the first three periods of the Periodic Table.

Identify an element from the first three periods that fits each of the following descriptions.

i) The element with the highest first ionisation energy.

ii) The element that forms a 1⁻ ion with the same electron configuration as helium.

iii) An element which forms a compound with hydrogen in which the element has an oxidation number of −4.

iv) The element in Period 3 which has the successive ionisation energies shown below in Table 1.

Table 1

Figure 1 below shows the successive ionisation energies for a period 2 element.

Figure 1

With reference to electronic structures, state the identity of this element and explain your answer.

This question is about the elements which have atomic numbers 33 to 37.

The first ionisation energies of these elements are shown in Table 1.

Table 1

i) Suggest the formulae of the hydrides of arsenic and selenium.

ii) Explain why the first ionisation energy of rubidium is lower than that of krypton.

iii) State which of the elements, arsenic to rubidium, has atoms with the smallest atomic radius.

The trend in melting points across period 3 can be broken down as follows:

Elements 1 to 3: General increase

Elements 4 to 8: General decrease

Explain this trend in melting point across the Period 3 elements.

This question is about hydrogen, the element with atomic number Z = 1.

Hydrogen can be placed in several different positions in periodic tables. One is immediately above lithium in Group 1. Another is in the centre of the first row, as shown in the AQA Data Sheet.

Evaluate the position of hydrogen when it is placed immediately above lithium and state one reason in favour and two against.

This question is about Period 4 of the Periodic Table.

i) State and explain which of K⁺ and Ca²⁺ is the smaller ion.

ii) Write the electron configuration for a Ca⁺ ion.

The first ionisation energies of the elements H to K are shown below in Figure 1.

Figure 1

State and explain the trend in first ionisation energies shown by the elements with the atomic numbers 2, 10 and 18.

The melting points of period 2 elements are shown in Table 1 below.

Table 1

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

Electrons in atoms occupy orbitals.

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

Figure 2

i) Complete the graph of the first ionisation energies for the next five elements.

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

The sequence of the first three elements in the Periodic Table is hydrogen, helium and then lithium.

Explain why the first ionisation energy of hydrogen is less than that of helium, but greater than that of lithium.

Compound J reacts with chlorine. The first five successive ionisation energies for an element J, are shown in Table 1.

Table 1

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

This question looks at the trends across a period in the periodic table. Four sequences of elements across period 3 are shown below:

Na, Mg, Al                   Al, Si, P                       Si, P, S                                    P, S, Cl

i) State which sequence shows the melting point increase across period 3?

ii) Two sequences contain elements that have the same structure in the solid state. Identify these two sequences and state the structure of each.

Nitrogen is a period 2 element that exists as a diatomic molecule. The first to third ionisation energies, in kJ mol^-1, of nitrogen are 1402, 2856 and 4578.

i) Write an equation representing the fourth ionisation energy of nitrogen.

ii) Suggest why the successive ionisation energies of nitrogen increase in value.

Table 1 below shows the successive ionisation energies of an unknown element, X. 

Table 1

Deduce the period and identity of element X and explain your answer with reference to its electron configuration.

First ionisation energies decrease down groups in the Periodic Table.

Explain this trend and the effect on the reactivity of groups containing metals.

The ionisation energy values show a general increase across period 4 from gallium to krypton.

i) State and explain how selenium deviates from this trend.

ii) Give one other element from period 2 or 3 which also deviates from this general trend, similar to selenium.

The ionisation energies of sodium, Na, are shown in Table 2 below.

Table 2

Show with a cross (x), in the third row of the table above, all the ionisation numbers that involve the removal of an electron from an s-orbital.