The IUPAC definition of an element states that ‘an element is metter, all of whose atoms are alike in having the same positive charge on the nucleus’. Each elemnt is given a symbol and these are predominentlly internationally recognized even if the names may differ in different languages.
Metals, non-metals and semi metals
Elements are classified as metals, non-metals and semi-metals. The names of almost all metals end in ‘-ium’, magensium, sodium, iridium, barium to just name a few. Common exceptions to this pattern are tin, lead, gold, silver, copper and et. cetra. We will look more closely at non-metals and semi-metals in later chapters.
Certain elements exists in more than one structural form and this property is referred to as allotropy. Carbon is a prime example of such a characteristic.
Shown in the figure below are the 8 known allotropes of carbon.
Take two of the most commonly quoted allotropes of carbon, diamond and graphite, both have infinite structures.
In the picture, diamond is on the left and graphite is on the right. They have drastically different appearances and physical properties. An obvious one may be that diamond is transparent and the graphite is opaque, this is primarily due to the different bonds and the structures they have which we will revisit in later chapters. However, both burn quite well under an oxygen-rich atmoshpere.
Diamond is extremely thermodynamically unstable at ambient temperature and pressure relative to graphite, thus if a conversion was to occur between the two allotropes, the conversion to graphite would be heavily favoured. As we see that people’s diamond wedding rings don’t simultaneously convert to coal, due to the fact that such a conversion is extremely slow. This phenomenon is referred to as metastability. This is especially interesting as you will learn that, in later chapters, what dictates the spontaneity of a reaction is the stability of the products relative to the reactants. In plain, simple, thermodynamics term, the conversion from diamond to graphite should be spontaneous, but is not. Other common elements that exsists in allotropic forms are sulfur, phosphorus, oxygen.
States of Matter
Temperature is defined as the average kinetic energy of the atoms/molecules. At a given temperature, an element is in one of three states of matter– solid,liquid or gas.
As seen above, in increasing of disorder, solid, liquid, and gas are three states of matter. In chemical euqations, the states of substances are notated using the following abbreviations:
(aq) symbolizes an aqueous solution, note that this is not a state of matter.