We use metals everyday. You’ll find metals like iron, nickel, chromium, aluminum and cobalt in objects such as cookware, cars and skyscrapers.
Metals make up more than 70 percent of the Periodic Table of the Elements – but many metals are unfamiliar to most of us.
Where Do Metals Come From?
We can find metal ores in the Earth itself, but many scientists believe that metal ores actually originated from Supernovae.
Thus, Carl Sagan’s phrase, “We are made of starstuff,” may also apply to our refrigerators and tire rims.
Once metal ores are processed, refined and alloyed, metals move throughout society, they find an amazing variety of uses. But – what is a metal?
So, What is a Metal?
Let’s turn to the Merriam-Webster Dictionary of the English Language to get a sense of how a metal is defined: We’ll get an impression of a complex substance that we take for granted:
“Any of various opaque, fusible, ductile, and typically lustrous substances that are good conductors of electricity and heat, form cations by loss of electrons, and yield basic oxides and hydroxides; especially: one that is a chemical element as distinguished from an alloy.“
Let’s simplify this definition through chemistry.
The Periodic Table Consists of a Continuum of Elements
There is a simple way to distinguish metals from non-metals in the Periodic Table. The more an element exhibits metallic properties, the greater tendency it has to form ionic, rather than covalent, bonds with other, less metallic atoms.
Chemist Linus Pauling introduced the concept of electronegativity in the 20th century. Simply put, the more readily an atom accepts additional electrons, the more electronegative it is.
Non-metallic elements such as fluorine, chlorine, and oxygen are highly electronegative. They tend to form negatively charged ions called anions. For example, the element fluorine readily forms the fluorine anion, F–.
Metallic bonds are bonds between metal atoms that exhibit special properties. Solids are rigid collections of atoms that form a matrix.
In most cases, the nuclei and the electrons are associated with specific nuclei. But metallic bonds possess greater electron freedom. Some of the electrons are loosely held – as a result, they offer a degree of mobility, that is, the ability to move around and throughout the matrix. This hallmark characteristic allows the flow of an electric current.
Thus, a metallic bond is one where the individual atoms form a crystal lattice, or matrix, and the conducting elements of the metal (electrons) move to allow a measure of heat, conduction of electricity or shaping of a metal to suit modern technology.
Defining Metals: Herzfeld’s Theory
One theory stands out in the characterization of metals – first elucidated in 1927 by Karl Herzfeld, although still incomplete. It characterizes metallic bonding simply as follows:
The element’s density, as determined by the gas phase volume of the metal, determines whether it is a metal or not. All metals, with the exception of mercury, which is a liquid, are in the solid phase.
This theory’s further development will come as technology streamlines methods to analyze elemental metals. The initial procedure of Herzfeld utilizes gaseous metals – oftentimes the solid metal elements must be vaporized to the gas phase. The temperatures can be upwards of 2000º Fahrenheit (1093º Celsius) and far greater. Beside the issues of metal toxicity, stand energy consumption and overall fire or explosion risk at such high temperatures. While the experimental results accurately account for the Periodic Table of the Elements, the theory, as it stands, is not complete.
As attempts to safely use Herzfeld’s theory to identify metals lagged, categorizing elements as conductors or semi-conductors has gained favor. Generally speaking, semi-conductors contain a combination of metals that conduct electricity and elements that don’t readily conduct electricity.
Mixed up descriptions between metals, non-metals, metalloids, and semi-conductors has made clear identification of metals confusing for many.
So, What is a Metal?
In short, to understand the differences between metals and non-metals – let’s say:
- Metals start appearing at the left of the Periodic Table – electronegativity decreases as one goes to the left, and down, in the Table.
- Metals form metallic bonds with one another, and ionic bonds with non-metals.
- Metals conduct heat and electricity.
- Metals are malleable (you can change a metal’s shape by physical means such as hammering without breaking it) and ductile (you can draw metal out into a wire, without losing its strength)
Decoding Science. One article at a time.