GCSE OCR Gateway C4:1a-b Noble gas properties

C4.1 Predicting chemical reactions of the noble gases

Summary

Models of how substances react and the different types of chemical reactions that can occur enable us to predict the likelihood and outcome of a chemical reaction. The current periodic table was developed based on observations of the similarities and differences in the properties of elements. The way that the periodic table is arranged into groups and periods reveals the trends and patterns in the behavior of the elements. The model of atomic structure provides an explanation for trends and patterns in the properties of elements. The arrangement of elements in groups and periods reveals the relationship between observable properties and how electrons are arranged in the atoms of each element.

Common misconceptions

Learners consider the properties of particles of elements to be the same as
the bulk properties of that element. They tend to rely on the continuous matter model rather than the particle model. Learners confuse state changes and dissolving with chemical changes. Also, since the atmosphere is invisible to the eye and learners rely on concrete, visible information, this means they therefore often avoid the role of oxygen in their explanations for open system reactions. Even if the role of oxygen is appreciated, learners do not realize that solid products of an oxidation reaction have more mass than the starting solid.

Underlying knowledge and understanding

Learners should be familiar with the principles underpinning the Mendeleev periodic table; the periodic table: periods and groups; metals and non-metals; the varying physical and chemical properties of different elements; the chemical properties of metals and non-metals; the chemical properties of metal and non-metal oxides with respect to acidity and how patterns in reactions can be predicted with reference to the periodic table.

C4.1a-b

To recall the simple properties of Group 0, both physical and chemical properties.

To be able to explain how observed simple properties of Group 0 depend on the outer shell of electrons of the atoms and predict properties from given trends down the groups including the ease of electron gain or loss.

Group 0 elements are the noble gases.

Structure

You can see that all noble gases are monomolecular.  Unlike halogens, which are all bimolecular, Noble gas atoms do not bond to each other covalently. 

Noble gas atoms exist independently from one another.

Bonding

Each atom bonds weakly to others via an induced dipole or London force.

The movement of electrons in the atom gives rise to an imbalance of electrons and a temporary or flickering dipole.

The more electrons in the Noble gas atom then the stronger is this temporary dipole.

What’s more this dipole can then induce a dipole in another atom. 

Melting and boiling points

As a result of this increase in the number of electrons per atom, the interatomic induced dipole forces increase down the group and therefore there is more energy required to separate these atoms and so the melting and boiling points increase going down the group.

Inertness

Most courses suggest you think about the inertness or the un-reactivity of the noble gases.

You can see from the table that all the noble gases have full outer electron shells.

The noble gas atoms it seems can neither share electrons to fill their outer shells nor lose or gain electrons in order to form ions and bond electrostatically with another element.

This is true for Helium, Neon and Argon.

But Krypton with four electron shells and Xenon with five etc. are able to accommodate more than eight electrons in their outer shells leading to the formation of compounds with the very electronegative non–metals like fluorine and oxygen.

For example XeF₄ Xenon tetrafluoride the first noble gas compound to be made.  The video below is from the Chem study program and discusses the formation of inert gas compounds. It shows samples of XeF4 and the properties of XeO3.  You can tell of course that the video clip is from 1963!!.

As this video clip shows there are more than eight electrons in the Xenon outer shell.

Density

Noble gas densities provide substance (!) to the proverbial lead balloon since Xenon is over eight times denser than air.  Density of air is 1.275 g/dm³ and Xenon has a density of 9.97 g/dm³

As this video shows Xenon sinks in air!!

The increased density going down the group is further evidence of stronger inter–atomic forces down the group.