Metals and nonmetals: A teaching plan

One of the competencies that students are expected to develop from the middlestage science curriculum is the ability to use observable properties of everyday materials to classify them as metals or nonmetals (see Box 1).^1,2 The concepts that support this competency are introduced gradually across different grade-level textbooks for preparatory-stage environmental studies (EVS) and middle-stage science.^3-7 I had the opportunity to explore this theme with 56 Grade IX students from three government senior secondary schools. When asked what they knew about metals, most students could list commonly taught properties— hardness, shine, malleability, ductility, and conductivity of heat and electricity—or provide examples such as gold and silver. To probe their understanding more deeply, I created a classroom display of 15 everyday objects and asked students to classify them into three categories—metals, nonmetals, or neither— based on observable properties (see the Activity Sheet). After completing the task, students were invited to justify their classifications. These discussions revealed significant gaps in their understanding of metals and nonmetals.⁸ In this article, I describe the key features of a teaching plan developed to address these gaps.

What are the properties of metals and nonmetals?

Middle-stage science textbooks introduce students to nine properties of metals (see Table I).^4,6,7 Most students were familiar with six. None mentioned sonority, corrosion on exposure to air and water, or the formation of alkaline oxides. Although students could recite textbook definitions of the six properties they were familiar with, they struggled to apply them accurately. For example, many students classified marble as a metal because it appeared shiny and malleable—they had seen polished, sheet-like marble floor tiles.⁸ This misunderstanding persisted despite explicit discussion in textbooks:

• Chapter 6 (‘Materials Around Us’) of the Grade VI science textbook (NCERT, Reprint 2025-2026) shares the following: “Are all lustrous materials metals? ‘All that glitters is not gold’ goes an old saying! Not all the materials that shine are metals. Surfaces of some materials are made shiny by polishing or coating them with thin layers of plastic, wax or any other material which makes them look shiny. These materials may not be them.“⁴ I explained that marble is not naturally lustrous like metals, but can be made shiny through polishing.
• Chapter 4 of the Grade VII science textbook (NCERT, 2025) shares the following: “Can you give some examples of metal sheets? You might have seen thin silver foil on some sweets and aluminium foil used for wrapping food items. These are formed due to their malleability. Gold and silver are the most malleable metals. A piece of coal or a lump of sulfur does not show this behaviour. They break into pieces and are said to be brittle. On the other hand, wood neither gets flattened into a sheet nor breaks into pieces. Therefore, wood is neither malleable nor brittle.“⁶ This chapter suggests that teachers allow students to try hammering a collection of metals and nonmetals to observe these differences for themselves. On asking, I found that none of the students had seen marble being hammered.

Discussion revealed that students had been introduced to the properties of metals and nonmetals as definitions to memorise, rather than as ideas to be explored through observation and activity. This was surprising, given that the textbook chapters on this theme include examples and activity ideas to help students develop a clearer understanding of these properties (see Table II).^3-7 Although some students recalled these activities being read aloud in class, none had actually performed them. To address this, we tried each of the activity ideas from Chapter 6 of the Grade VI textbook (NCERT, Reprint 2025-2026) and Chapter 4 of the Grade VII textbook (NCERT, 2025).^4,6 For example, I brought the following samples to class: iron nails, pieces of coal, bricks, pieces of marble, pieces of hard plastic, thick copper wires, artificial gemstones, graphite rods, thick aluminium wires, coins, etc. Students observed and recorded what happened when each sample was struck with a hammer—did it flatten into a sheet or break into pieces? At the end of this exercise, I compiled their observations on the board and used them to discuss malleability. When asked which materials were malleable, none of the students mentioned marble. When asked why, they explained that it had broken into pieces when hammered. I confirmed that marble is not malleable and clarified that the sheet-like tiles they had seen were produced by cutting and polishing, not by hammering.

Are all materials either metals or nonmetals?

Six of the 15 objects used in the initial classification activity—wood, plastic, chalk, marble, brick, and the green board—were neither metals nor nonmetals. Although students had the option to use this category, very few did so (see Table III).⁸ Discussion revealed that many students believed that all materials must be either metals or nonmetals. As a result, they relied on the metal properties they were familiar with to classify objects into these categories:

• Objects that showed one or more of these properties were often classified as metals. For example, over half the students classified wood and plastic as metals because they were hard. Some noted that plastic could appear shiny, while others referred to plastic sheets and insulated wires to argue that plastic was malleable and ductile.
• Objects that did not show these properties were typically classified as nonmetals. Chalk, for example, was widely classified as a nonmetal because it was neither hard nor shiny—two properties many students believed all metals must possess.

Chapter 4 of the Grade VII science textbook (NCERT, 2025) defines nonmetals in the following way: “Substances like sulfur and phosphorus… are usually soft and dull in appearance. They are neither malleable nor ductile, and they are not sonorous. They are also poor conductors of heat and electricity. These are called nonmetals. Their oxides are acidic in nature. Some other nonmetals are oxygen, hydrogen, nitrogen, carbon, etc.“⁶ But this chapter also points out that nonmetals “…must not be confused with materials such as plastic, glass, wood, rubber, and paper. These materials are not classified as metals or nonmetals because they are not elements.“⁶ It then introduces students to the term ‘elements’: “Metals and nonmetals are sub-categories of substances called elements. An element is a substance that cannot be broken down into simpler substances. in nature. Presently, 118 elements are known. These elements are the basic building blocks of all matter.“⁶ I discussed these ideas in more detail with the students. I then displayed a periodic table, highlighting only those elements that are mentioned in the preparatorystage EVS and middle-stage science curricula (see Fig. 1). Among metals, I highlighted sodium, potassium, magnesium, calcium, iron, cobalt, nickel, copper, zinc, gold, silver, mercury, and aluminium. Among nonmetals, I highlighted carbon (including coal, graphite, and diamond), hydrogen, nitrogen, oxygen, sulphur, and iodine. This provided an opportunity to explain that while most metals and nonmetals showed the properties listed in their textbooks, there are some exceptions. I reminded the students that:

• Most of them (43 of 56 students) had classified mercury as a nonmetal because it is a liquid at room temperature and lacks hardness, lustre, malleability, and ductility.
• Most of them (45 of 56 students) had classified diamond as a metal because of its hardness and shine.
• Most of them (43 of 56 students) had classified graphite as a metal because it is shiny and conducts electricity—something the students had tested using a simple circuit provided in class.⁸

I also pointed out that:

• Not all elements are metals or nonmetals; some are metalloids. Metalloids show properties of both (for example, they are hard and solid, but brittle and non-sonorous).⁹
• Not all materials are elements. Some are compounds, and others are mixtures. Both these materials can contain metals and/or nonmetals. But compounds “…are formed when different elements combine in fixed ratios to form something entirely new.“⁹ So the properties of compounds are different from their constituent elements. In contrast, mixtures are formed when “…two or more substances are mixed, where each substance retains its properties.“⁹ Here, I drew the students’ attention to the coins and the steel spoon. Fifty-five of 56 students had classified both as metals because of properties such as shine, hardness, malleability, and electrical conductivity (which they had tested using the circuit). I confirmed that both objects do show metal-like properties, but explained that they are alloys. This concept of alloys as “mixtures of metals” is first introduced to students in Chapter 10 (‘This World of Things’) of the Grade IV EVS textbook (NCERT, 2024).³ This chapter includes the following note to the teacher: “Show the children some common metals around you, such as iron, copper, aluminium, gold, silver, mercury in a thermometer or alloys such as steel, brass, and bronze.“³ It also suggests some activity ideas for the classroom (see Table IV).³ I supplemented this discussion by showing the students a collection of everyday objects made of different alloys, including cutlery, tools, doorknobs, medals, cans, pipes, and simple jewellery.

Parting thoughts

A month after the initial exercise, I invited students to repeat the classification activity. During their first attempt, the students had based their classification mainly on: (a) Their ability to identify materials mentioned as examples of metals or nonmetals in the middle-stage science textbooks, and (b) The presence or absence of 1-2 properties, typically hardness and shine. This time, the students analysed the objects for the presence or absence of each of the seven physical properties they had learned to associate with metals. After the students had finished the exercise, I asked if they could identify one property in the list that all metals show and no nonmetals show. The answer was, “No.” When asked about hardness and shine, most students agreed that neither property was, alone, sufficient to classify a material as a metal. When asked why, they explained that mercury is a metal, but not hard; while diamond and steel are hard and shiny, but not metals. I then drew attention to the wording used in Chapter 4 of the Grade VII science textbook (NCERT, 2025): “We learnt that metals are generally hard, lustrous, malleable, ductile, and good conductors of heat and electricity.“⁶ Emphasising the word ‘generally’. I suggested that analysing a material’s composition and observing as many of its properties as possible can make our classification of it more accurate. We ended the class on this note.