Lead is a chemical element1 – a substance that contains only one type of atom2. Its official chemical symbol is Pb, and its atomic number3 is 82, which means that a lead atom has 82 protons in its nucleus4. Lead has the highest atomic number of any stable (non-radioactive) element. It is a dense, heavy metal5 – yet it is soft and can be shaped and stretched without breaking.
Lead’s chemical symbol – Pb – comes from the Latin word plumbum. The Roman Empire used lead to make waterpipes, so the word plumbum was associated with systems that carried water into buildings. Today, we call this plumbing and those who work with it plumbers.
A similar word, plumbago, also has an association with lead and it has caused misconceptions for centuries. Plumbago (also known as black lead) is actually graphite. The soft black substance in your wooden pencil has never been made of lead.
Metals of antiquity
Lead is one of the seven metals of antiquity – metals that humans identified and used in ancient times. The other metals of antiquity are gold, silver6, copper7, tin8, iron9 and mercury10. Each metal was associated with one of the seven known celestial bodies. Gold11, for example, was associated with the Sun due to its colour and value. Lead was the least desirable of the ancient metals due to its dull grey colour and heaviness, so it was associated with Saturn – the furthest of the known planets.
Fast forward to the Middle Ages, and lead became an object of great interest to alchemists. Alchemy was a mix of chemistry and philosophy that sought to turn lead into gold. Alchemists thought that all metals were made of the same substance, but metals like lead were spiritually and physically immature forms of the higher metals. With refinement, lead could become spiritually perfect just like gold. Even famous scientists like Sir Isaac Newton dabbled in alchemy.
Nature of science
It this era of modern science, the historical mix of science, philosophy and religion may appear unusual. All scientific knowledge is produced within a larger society and culture. The tentative12 scientific knowledge of ancient and classical civilisations was influenced by cultural aspects of the time. As new information was discovered, the old ways of thinking were discarded.
Uses of lead
Lead is usually found as an ore13 – in combination with other elements14 such as silver. This type of ore has a low melting point15 so it was relatively easy to smelt16, and lead became a byproduct17 of the more valuable silver. Humans have been making items from lead for around 9,000 years. The ancient Egyptians and Greeks used lead in cosmetics, glass and enamels. Other early civilisations used lead to make coins, as a writing material and for medicinal purposes.
During the Middle Ages, lead was commonly used in roofing and piping due to its malleability and durability. In 1160, builders used 182 tonnes of thin lead panels to cover the roof of Notre Dame Cathedral, and later 680 tonnes went into its spire. Lead was also a key component in the construction of firearms and printing presses. Lead production increased during the Industrial Revolution18 due to a growing demand for lead paints and plumbing.
Some ancient uses of lead continue today – weights, roofing materials, organ pipes and sculptures. Other uses are more modern – radiation19 shields in medical X-ray20 rooms and nuclear science labs and in lead-acid batteries.
Lead plays a part in protecting important New Zealand buildings like the Museum of New Zealand Te Papa Tongarewa. The buildings use base isolators to protect them during an earthquake. The lead core deforms21 during an earthquake, absorbing some of the energy, and then reverts to its original shape.
Concerns about lead poisoning
It was during the Industrial Revolution that doctors noticed diseases22 like gout23 were more commonly found in painters and plumbers than in the rest of the population. Other health issues – including blindness, anaemia and kidney and brain damage – convinced officials to create laws that decreased the public’s exposure to lead. In New Zealand, lead was removed from all but clearly labelled special-purpose paints in 1965 and banned from petrol in 1996.
The useful links section at the end of this article has information regarding lead poisoning, treatment and prevention.
Nature of science
Science and society can have differing views on an issue. When it was proposed to add lead to petrol in the 1920s, scientists advised that it would be dangerous to people and the environment. The desire for cheaper fuel24 and safer cars prevailed, and lead was added. As scientific evidence25 on the dangers of lead grew, public intolerance of lead also grew, and leaded petrol was banned.
Useful links
The New Zealand Ministry of Health has information regarding:
- lead poisoning – symptoms, treatment and prevention
- managing lead-based paint
- element: A substance made of atoms that all have the same atomic number. Elements cannot be split into simpler substances using normal chemical methods.
- atom: The smallest possible unit of matter that still maintains an element’s identity during chemical reactions. Atoms contain one or more protons and neutrons (except hydrogen (H), which normally contains no neutrons) in a nucleus around which one or more electrons move.
- atomic number: The number of protons in the nucleus of an atom. This determines an element’s properties and location on the periodic table of elements.
- nucleus: 1. The very small, very dense, positively charged centre of an atom containing protons and neutrons. 2. Part of the cell that contains the cell’s hereditary information (DNA) and controls the cell’s processes.
- metal: Any of a category of elements that usually have a shiny surface, are generally good conductors of heat and electricity and can be melted or fused, hammered into thin sheets or drawn into wires (for example, copper).
- silver: A transition metal in Group 11 of the periodic table – symbol Ag, atomic number 47.
- copper: A transition metal in Group 11 of the periodic table – symbol Cu, atomic number 29.
- tin: A metal – symbol Sn, atomic number 50.
- iron: A chemical element with the symbol Fe.
- mercury: 1. A transition metal in Group 12 of the periodic table – symbol Hg, atomic number 80. 2. Mercury is also the smallest and innermost planet in our Solar System.
- gold: A transition metal in Group 11 of the periodic table – symbol Au, atomic number 79.
- tentative: Not certain or fixed.
- ore: Rock or sediment from which we can extract elements and minerals.
- element: A substance made of atoms that all have the same atomic number. Elements cannot be split into simpler substances using normal chemical methods.
- melting point: The temperature at which a substance changes state from a solid to a liquid.
- smelt: To get metal from rock by heating it to a very high temperature. To melt objects made from metal in order to reuse the metal.
- byproduct: A secondary product produced during manufacturing, mining or refining. Something unexpected or unintended caused as a result of something else.
- Industrial Revolution: The engineering revolution in the late 1700s and early 1800s that powered factories, railroads and steam ships and mechanised agriculture and textile manufacturing, leading to huge changes in society. It was not until the mid 20th century that the rise in CO2 emissions from burning fossil fuels became significant.
- radiation: Energy that is transmitted (radiates) from a source in the form of rays or waves or particles.
- X-ray: A form of electromagnetic radiation with a wavelength of 0.01 to 10 nanometres. X-rays are used in medical fields as an imaging technique.
- deform: To change shape.
- diseases: 1. An abnormal condition of an organism that impairs bodily functions. 2. In plants, an abnormal condition that interferes with vital physiological processes.
- gout: A painful inflammation of the joints caused by a build-up of uric acid in the blood and crystallising in joints.
- fuel: 1. A combustible substance that provides energy. 2. A body fuel such as fat, carbohydrates and protein that supplies energy for animals’ activities.
- evidence: Data, or information, used to prove or disprove something.