States of matter

According to studies by Piaget and Inhelder (1974), children maintain a naive view on the states of matter, such as matter can cease to exist, weight is not an intrinsic property of matter, or that physical transformations aren’t reversible. 

This chapter, by Vanessa Kind will deconstruct these assumptions and explore the implications for teaching. 

A naive view of matter

“There are more than three kinds of ‘stuff’… ”

Direct sensory experience leads children to a naive view of matter involving more than three states, which Hayes (1979) suggests is something like this:-

“There are different kinds of stuff: iron, water, wood, meat, stone, sand etc. And these exist in different kinds of physical state: solid, liquid, powder, paste, jelly, slime; paper-like etc. Each kind of stuff has a usual state: iron, solid, water, liquid, sand is powder, etc., but this can sometimes be changed. For example, many stuffs will melt if you make them hot enough…and others will burn. Any liquid will freeze if you make it cold enough. Any solid can be powdered… There is no obvious standard way of changing a powder to a solid… Some solids decompose, i.e. change slowly into some other (useless) substance; or mature, i.e. change slowly into some other (useful) substance…” (p 242-70).

Stavy and Stachel (1985) examined the conceptions children aged between 5 and 12 have of `solid’ and `liquid’ and found evidence to support Hayes’ view. Children think of like metals and wood as typical solids. To them, substances which are not hard, and rigid cannot be solids, so classifying solids which do not “fit” this image is difficult.

These researchers found that 50% of 12- and 13-year-olds classify non-rigid solids such as dough, sponge, sand and sugar separately from coins, glass or chalk. They suggest that:- “The easier it is to change the shape or the state of the solid, the less likely it is to be included in the group of solids.” (p 418) Water is the standard “liquid” against which other possible liquids are compared.

Children find that pourable powders have liquid properties but do not produce a sensation of wetness, so classify these independently. Children think of water as a typical liquid. Stavy and Stachel found that in general children classify new liquids more easily than solids, perhaps because liquids are less varied in their physical characteristics.

Children appear to rely solely on sensory information when reasoning about matter up to the age of around 14 years. Abstract ideas such as ideas about particles are not readily used to answer questions about the properties of matter, so children persist in thinking that substances are continuous.

Millar (1989) suggests that children do not need to use particle ideas because their own theory of matter has worked perfectly well for them. This has implications for influencing change in students’ ideas.

Gases

Gases cause special difficulties for children since those commonly experienced, like air, are invisible. Stavy (1988) suggests this invisibility prevents children from forming a concept of gas spontaneously. She finds instruction is needed for children to acquire knowledge about gas properties, whereas her earlier work suggests that children learn intuitively about solids and liquids. Gases are also conspicuously absent from Hayes’ characterisation.

Séré (1986) investigated the ideas 11 year olds have about gases prior to teaching. She found that children associate gases with the use and function of objects, like footballs, tyres and suction pads. Expressions like “hot air rises” (but not “cold air sinks”) and “air is everywhere” were commonplace. Also, air was frequently described as being alive, for example, “air always wants to expand everywhere”. These ideas may arise through experience of draughts and wind as well as using air around the home.

Naive ideas about the properties of matter

” ‘Stuff’ can disappear but its taste and smell stay behind…”

Children’s ideas about the behaviour of matter were studied by Piaget and Inhelder (1974). They formulated children’s naive view of matter as follows:-

“a. Matter has no permanent aspect. When matter disappears from sight (e.g. when sugar dissolves in water) it ceases to exist.

b. Matter has a materialistic core to which various random properties having independent existence are attached. Matter can “disappear,” whereas its properties (such as sweetness) can continue to exist completely independently of it.

c. Weight is not an intrinsic property of matter. The existence of weightless matter can be accepted.

d. Simple physical transformations (such as dissolution) are not grasped as reversible.” (quoted in Stavy, 1990a, p 247)

Research evidence supports these statements. For example, Russell et al (1989 and 1990) asked children aged 5 - 11 to explain the decrease in water level in a large tank after sunny weather. About 45% focused on the remaining water, seeing no need to explain where the “missing” water had gone. For these children the matter had simply ceased to exist (statement `a’).

Stavy (1990a) studied 9 - 15 year olds’ abilities to conserve weight and matter. Her students were shown propanone evaporating in a closed tube. Around 30% of 9 - 10 year olds in her sample thought the propanone disappeared (statement b). She also found that 30% of the 10 - 12 age group (30%) thought the smell of the propanone remained, although the matter vanished.

Prieto et al (1989) reports that 44% of 14 year olds think a solute “disappears” when dissolved, while 23% label the event “it dissolves” with no explanation. A further 40% of this age group in the Stavy (1990a) study thought that propanone became weightless because it had become invisible (statement `c’).

By the age of 15, Stavy (1990a) found that 65% view the evaporation of propanone as reversible, with a large jump in proportion from 25 to 60% at age 13 - 14 when formal teaching about particle ideas is received (statement d).

Implications for teaching

The impact of the “naive view” on teaching about states of matter

The naive views of matter described by Hayes and Piaget and Inhelder point to three key features of children’s reasoning about matter important in teaching. These are:-

(i) children do not reason consistently - they may use sensory reasoning on some occasions and logical reasoning on others;

(ii) sensory experience dominates in cases where the matter is not visible, leading to the fact that

(iii) many students aged 15 and over still use sensory reasoning about matter, despite being well advanced in thinking logically in other areas, such as mathematics.

Evidence supporting these points includes Stavy’s study (1990a), which reports that children reason differently when the substance studied remains visible. Propanone evaporates to form an invisible gas, but solid iodine produces a purple vapour which can be seen. As well as the propanone problem, children explained what they thought occurred when solid iodine was placed in a closed tube and heated to produce the purple vapour. This time, 30 - 50% of children across the 9 - 15 year old age range perceived that the weight of the material was unchanged, while 70 - 95% thought the matter itself was conserved. These contrast with the figures reported earlier for the propanone demonstration.

Stavy’s work indicates that 30 - 40% of 15 year olds who have received teaching about the particle theory still use naive ideas about matter in solving particle problems. The Children’s Learning In Science (CLIS) project (Brook, Briggs and Driver, 1984) found similar results. Children’s naive view of matter, acquired through long experience from childhood, is sufficiently strong to be difficult to relinquish and inhibits consistent thinking about matter. So, although children may have the necessary skills to answer correctly questions about matter which require logical or abstract thought, their naive view leads them to incorrect ideas.

The implications of the persistence of a naive view of matter are wide-ranging, as discussion on the learning of the particulate theory of matter will indicate. Suggested activities follow at the end of section 2.