Fourteen elements are nearly always included in the list of non-metal elements, with up to about nine more elements sometimes added, including gases (hydrogen, helium, nitrogen, oxygen, fluorine, neon, chlorine, argon, krypton, xenon and radon), a liquid (bromine), and some solids (carbon, phosphorous, sulphur, selenium, and iodine). All of these elements act as the basic building blocks for organic compounds and display a range of properties in terms of their atomic and chemical behaviour.
These behavioural differences are a result of differences in interatomic and intermolecular bonding strengths, yet most have some common properties, including:
- form ionic/covalent bonds
- brittle and non-malleable
- low melting/boiling points
- High ionisation energy and electronegativity
- poor conductors of heat and electricity
Not all non-metals display all of these common properties, with carbon, for example, being a good conductor of electricity while many polymers are malleable and easily shaped.
Non-metals include all of the elements in the S-block of the periodic table and around 58% of those in the P-block.
Chemically-speaking, non-metals can be divided into two types:
- Covalent materials that contain atoms with small sizes, high electro-negativities, low valence vacancy to electron ratios and a tendency to form negative ions during chemical reactions and have negative oxidation states in their compounds.
- Ionic materials, containing both large and small atoms, the ions can be formed by adding or extracting electrons to atoms. In these materials, the non-metals either exist as monatomic anions or as constituents of polyatomic anions.
Non-metals can also be categorised as reactive non-metals (Hydrogen (H), Carbon (C), Nitrogen (N), Oxygen (O), Phosphorous (P), Sulphur (S), Selenium (Se)), halogens (Fluorine (F), Chlorine (Cl), Bromine (B), Iodine (I), Astatine (As)), and noble gases (Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn), element 118 (oganesson Og)).
Hydrogen is classified as being a non-metal, but it displays unique properties that differ from other non-metals and make it hard to categorise. Naturally exiting as a gas, hydrogen forms covalent bonds like other non-metals, but it can also shed its single electron and form positively charged ions, like a metal. This unique mix of properties led the physicists Hillard Huntington and Eugene Wigner to predict in 1935 that hydrogen would condense to a metallic liquid or solid under extremely high temperatures or pressures. This phase of hydrogen is predicted to behave like metal and become a good conductor of electricity and heat. It is believed that liquid metallic hydrogen may exist in the core of gas giant planets like Saturn and Jupiter, which would explain the powerful magnetic fields of these planets. However, for now at least, hydrogen remains a non-metal.
Non-metallic materials can be made from both organic and inorganic compounds and include a range of different composites, polymers, textiles and vinyls.
Common examples of widely-used non-metallic materials include:
- Adhesives
- Ceramics
- Cork
- Fibre
- Felt
- Lubricants
- Plastic (thermoset and thermoplastics)
- Rubber
Non-metallic substances have unique properties that lend them a range of advantages over metals:
1. Cost
Non-metallic materials tend to cost much less than their metal counterparts.
2. Obtainable
Non-metallic materials can be produced and obtained much faster than many metals, allowing you to increase production efficiencies.
3. Favourable Properties
The properties of non-metals can make them preferable to metals in certain applications. The lack of electrical conductivity mean that non-metals can be used as electrical insulators and their low heat conduction means that they can be used as heat-resistant applications, such as the handles of saucepans. Non-metal materials are also more resistant to chemicals and corrosion than metals, allowing them to be used in harsh environments.
The various advantages of non-metals mean that there is a range of practical applications for non-metallic materials, including:
- Insulators: Since non-metallic parts do not conduct electricity, they make good insulators for electrical parts and wiring
- Oil and Gas Production: The corrosion-resistant and lightweight properties of non-metals allow them to be readily used for pipes and liners in the oil and gas industry.
- Fuel: Carbon has been used as a fuel source for centuries, mostly in the form of coal.
- Automobile, Aircraft and Ship Construction: Because they are lightweight, many non-metal parts, such as plastic and fibreglass, are used in the automotive, aerospace and marine industries.
- Tapes and Adhesives: Non-metallic materials are used for tapes and adhesives as they can withstand extreme conditions like corrosion and heat.
- Sealing: Due to their ability to remain effective under a range of conditions, non-metals make good seals.
- Foam and Rubber: Non-metallic materials such as foam and rubber are common in a variety of applications.
What are the Two Groups of Non-Metallic Materials?
From a chemical standpoint, non-metallic materials can be divided into covalent and ionic materials. These include gases, liquids and solid materials and can be reactive materials, halogens or noble gases.
What are Non-Metallic Objects?
Non-metallic object are those that do not contain metal elements. They typically have low thermal or electrical conductivity and show good resistance to chemicals and corrosion.
What are some Examples of Non-Metallic Elements?
Non-metallic elements in the periodic table include hydrogen, carbon, nitrogen, oxygen, phosphorous, sulphur, silicon, boron, tellurium and selenium. They also include halogens (fluorine, chlorine, bromine, iodine and astatine) and noble gases (helium, neon, argon, krypton, xenon and radon).
What are the 5 Non-Metallic Properties?
Non-metals are often said to have five properties in common, however, not all non-metals possess all of these properties. While most non-metals have a low melting point, salt, for example, has a very high melting point of 801 °C.
Despite the exceptions, the generally accepted properties of non-metals are:
1. Form Covalent/Ionic Bonds
Non-metals form covalent or ionic bonds to create chemical compounds.
Covalent bonds are when two elements share valence electrons until a complete shell is formed. Covalent compounds include ethanol, glucose and carbon dioxide. Covalently bonded compounds share electrons between the elements within them to achieve a stable electron configuration and tend to show the widest variation in molecular geometry. Covalent compounds also take on shapes that minimise the amount of electrostatic repulsion between electron pairs.
Ionic bonds form with one element taking electrons from another to create a cation and an anion. Oppositely charged ions attract one another, joining together to form an ionic compound. These compounds include table salt, carbonate, sulphate and potassium chloride. Most ionic compounds arrange themselves into a lattice structure and tend to form between elements with differing electro-negatives (ΔEN > 2.0).
2. Brittle
Whether formed of ionic or covalent bonds, most non-metals are brittle and will shatter under force, unlike metals, which are malleable and ductile. Most non-metal compounds lose their strength when moulded and cannot be deformed past a set point without breaking.
The nature of the covalent or ionic bonds is the reason for the brittleness of non-metals, as both arrange the shared or captured electrons to minimise electrostatic repulsion. In an ionic compound, the positive and negative electrons are locked together in a crystal structure. Force can shift this structure so that, instead of negative electrons being aligned to positive electrons, positives align with positives and negatives with negatives, causing a repulsion that fractures the compound. Covalent bonds also form in a particular way that can be disturbed through the application of mechanical force, fracturing the compound.
Metals, by contrast, have delocalised electron bonds that can move and slide past each other without breaking, lending metal its ductile and malleable nature.
3. Low Melting/Boiling Points
While not all non-metallic compounds have low melting and boiling points, they do tend to have lower melting and boiling points than metals, which is why many non-metals are gaseous at room temperature.
The low melting and boiling points are because of the relatively weak intermolecular interactions in non-metals, and is more pronounced with covalent compounds than ionic ones. The strength of intermolecular structure informs a material’s phase behaviour, with metals showing strong intermolecular attractions compared to most non-metals. Covalent compounds have the weakest intermolecular attractions as they are electrically neutral. Ionic compounds are stronger than covalent compounds but as they are heated the kinetic energy of the particles in the ionic compound increases. This kinetic energy eventually overcomes electrostatic attraction, causing the lattice structure to break apart.
4. High Ionisation Energy/Electronegativity
Non-metal atoms tend to have high levels of ionisation energy, which mean it is difficult to remove electrons from them. This high ionisation energy is due to the large size of their nuclei as compared to how full their electron shells are. These large, positively charged nuclei attract their electrons strongly, making them difficult to remove. This attraction can even remove electrons from neighbouring atoms and explains why non-metals tend to be electro-negative than metals. These high ionisation energies and electro-negativities increase as you move left on the periodic table.
5. Poor Conductors of Heat and Electricity
Non-metals tend to be poor conductors of heat and electricity, although there are some exceptions to this rule. Metals can absorb a lot of kinetic heat energy without breaking their bonds while they also have lots of open orbitals that electrons can move through, making them good conductors of electricity too. Non-metals, by contrast, have structures that break under kinetic energy and full orbitals that block electrons when a voltage is introduced.
Non-metals are typically gaseous or liquid at room temperature and can be divided into reactive non-metals, halogens and noble gases. They form covalent or ionic bonds and tend to be brittle with low melting/ boiling points and high ionisation energies and electro-negativity, as well as being poor electrical conductors.
Non-metallic materials are widely used across a range of industries for a wealth of applications, from composites used in aerospace to polymer pipes used to transport fluids and liquids. Rubber, vinyl and ceramic are all commonly used non-metallic materials, as well as adhesives and sealants.