2.1 The Periodic Table: Chemical Periodicity

An element X reacts according to the following sequence.

What could be element X?

Use of the periodic table is relevant to this question.

Sir Humphrey Davy discovered the elements magnesium, boron, sodium and calcium.

Which of the elements Sir Davy discovered has the third lowest first ionisation energy in its period and the third smallest atomic radius in its group?

When solution X is titrated against hydrochloric acid, a neutralisation reaction occurs.

Which of the following hydroxides is not solution X?

G and J are oxides of different Period 3 elements.

If one mole of J is added to water, the solution formed is neutralised by exactly one mole of G. 

What could be the identities of G and J?

Shown on the graph are the relative values of the first ionisation energies of four elements that have consecutive atomic numbers. One of the elements reacts with hydrogen to form a covalent compound with formula HX. 

Which element could be X?

Mohr’s salt is a pale green crystalline solid which is soluble in water. It contains two cations, of which one is Fe²⁺ and one anion which is SO₄^2-.

The second cation was determined by heating solid Mohr’s salt with solid sodium hydroxide, and a colourless gas was evolved. The gas readily dissolved in water giving an alkaline solution.  

A grey-green solid residue was also formed, which was insoluble in water. 

Which row correctly identifies the colourless gas and the grey-green residue?

Bacteria in swimming pools are killed by adding aqueous sodium chlorate (I), NaOCl. This reacts with water to produce HOCl molecules which can breach the bacteria cell wall and kill the bacteria. The reaction below shows the reaction with water:

OCl^– (aq) + H₂O    OH^– (aq) + HOCl (aq)

Under the sun’s UV rays, the OCl^– ion is broken down by ultra-violet light:

    OCl^– (aq) + uv light  Cl^– (aq) + ½O₂ (g) 

Which method would maintain the highest concentration of HOCl (aq)?

The table gives the successive ionisation energies for an element R.

What could be the oxidation state of element R in its chloride?

Which row describes a ceramic material?

What is the correct order of the decreasing melting points of the four chlorides shown?

                                        HCl      MgCl₂      CCl₄       S₂Cl₂

Consecutive elements X, Y and Z, are in the third period of the Periodic Table. Element Y has the highest first ionisation energy and the lowest melting point of these three elements.

What could be the identities of X, Y and Z?

The period 4 elements gallium (Ga), germanium (Ge), arsenic (As) and selenium (Se) are the elements directly below aluminium, silicon, phosphorus and sulfur in the Periodic Table.

The properties of each period 4 element resemble those of the period 3 element directly above it. 

Which period 4 elements form oxides that dissolve in water to give an acid solution?

Which graph correctly shows the relative melting points of period 3 elements plotted against their relative electronegativities?

A table of four substances and their physical properties is shown.

Which substances have the correct properties?

Non-metallic elements and their atoms can have the two following properties.

Property 1:     Has no paired 3p electrons 

Property 2:     Has an oxide that can form a strong acid in water

Which properties do phosphorus and sulfur have?

Use of the periodic table is relevant to this question.

Elements X and Y react together to form compound Z. Elements X and Y are both in Period 3. Element X has the second smallest atomic radius in Period 3. Apart from argon, there is only one element in Period 3 which has a lower melting point than element Y.

Which compound could be Z?

Which properties do compounds of silicon and aluminium have in common?

Period 3 elements can react with chlorine to produce the following chlorides:

MgCl₂       AlCl₃      SiCl₄      PCl₃      SCl₂

Period 3 elements also react with oxygen to produce oxides.

When the oxides are produced is when the period 3 element is in its highest possible oxidation state. Which of the elements have a higher oxidation number than in the above chlorides?