The key difference between graphite and lead is that graphite is nontoxic and highly stable, whereas lead is toxic and unstable.
Graphite and lead are very useful in the manufacture of pencils. In the past, pencils were made with lead, but modern pencils do not have lead at all. They are now made of graphite, which is safe and is a form of carbon.
CONTENTS
1. Overview and Key Difference
2. What is Graphite
3. What is Lead
4. Graphite vs Lead in Tabular Form
5. Summary – Graphite vs Lead
What is Graphite?
Graphite is an allotrope of carbon having a stable, crystalline structure. It is a form of coal. Furthermore, it is a native mineral. Native minerals are substances containing one chemical element that occurs in nature without combining with any other element. Moreover, graphite is the most stable form of carbon that occurs at standard temperature and pressure. The repeating unit of the graphite allotrope is carbon (C). Graphite has a hexagonal crystal system. It appears in an iron-black to steel-grey colour and also has a metallic lustre. The streak colour of graphite is black (the colour of the finely powdered mineral).
The graphite crystal structure has a honeycomb lattice. It has graphene sheets separated at a 0.335 nm distance. In this structure of graphite, the distance between carbon atoms is 0.142 nm. These carbon atoms bind to each other via covalent bonds, one carbon atom having three covalent bonds around it. The valency of a carbon atom is 4; thus, there is a fourth unoccupied electron in each and every carbon atom of this structure. Therefore, this electron is free to migrate, making graphite electrically conductive. Natural graphite is useful in refractories, batteries, steelmaking, expanded graphite, brake linings, foundry facings, and lubricants.
What is Lead?
Lead is a chemical element having atomic number 82 and the chemical symbol Pb. It occurs as a metallic chemical element. This metal is a heavy metal and is denser than most of the common materials we know. Furthermore, lead can occur as a soft and malleable metal having a relatively low melting point. We can easily cut this metal, and it has a characteristic blue hint along with the silvery grey metallic appearance. More importantly, this metal has the highest atomic number of any stable element.
Lead is a relatively unreactive post-transition metal. We can illustrate the weak metallic character of lead using its amphoteric nature. E.g. lead and lead oxides react with acids and bases and tend to form covalent bonds. Compounds of lead often have a +2 oxidation state of lead rather than the +4 oxidation state (+4 is the most common oxidation for group 14 chemical elements).
When considering the bulk properties of lead, it has a high density, malleability, ductility, and high resistance to corrosion due to passivation. Lead has a close-packed face-centered cubic structure and a high atomic weight, which results in a density that is greater than the density of most common metals such as iron, copper, and zinc. When compared to most metals, lead has a very low melting point, and its boiling point is also the lowest among group 14 elements.
Lead tends to form a protective layer upon exposure to air. The most common constituent of this layer is lead(II) carbonate. There can also be sulfate and chloride components of lead. This layer makes the lead metal surface effectively chemically inert to air. Furthermore, fluorine gas can react with lead at room temperature to form lead(II) fluoride. There is a similar reaction with chlorine gas as well, but it requires heating. Apart from that, lead metal is resistant to sulfuric acid and phosphoric acid but reacts with HCl and HNO3 acid. Organic acids such as acetic acid can dissolve lead in the presence of oxygen. Similarly, concentrated alkali acids can dissolve lead to form plumbites.
Since lead was outlawed in the USA in 1978 as an ingredient in the paint due to toxicity effects, it was not used for pencil production. However, it was the main substance used for pencil manufacturing before that time. Lead was recognized as a quite toxic substance to humans. Therefore, people searched for substitute materials to replace lead with something else to manufacture pencils.
What is the Difference Between Graphite and Lead?
Graphite and lead are important chemical elements due to their useful properties and applications. The key difference between graphite and lead is that graphite is nontoxic and highly stable, whereas lead is toxic and unstable.
The following table summarizes the difference between graphite and lead.
Summary – Graphite vs Lead
Toxicity is an important measure in using a chemical material in a particular industry. The key difference between graphite and lead is that graphite is nontoxic and highly stable, whereas lead is toxic and unstable.
Reference:
Kruszelnicki, Karl S. “Lead in Your Pencil.” ABC (Australian Broadcasting Corporation), 8 Sept. 2004.
Image Courtesy:
1. “Kimmirut Graphite” By Mike Beauregard from Nunavut, Canada – Kimmirut Graphite (CC BY 2.0) via Commons Wikimedia
2. “Lead electrolytic and 1cm3 cube” By Alchemist-hp (talk) (www.pse-mendelejew.de) – Own work (FAL) via Commons Wikimedia