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Observe and Wonder
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Asking Scientific Questions about Matter and its Interactions
Atoms and Molecules
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Indivisibility of Atoms: Some students believe atoms are the smallest unit and cannot be broken down further, unaware of subatomic particles like protons, neutrons, and electrons.
Perceptibility: Given the illustrations in textbooks, students might think atoms and molecules can be seen with advanced microscopes. In reality, they are too small to be directly observed, even with electron microscopes.
Static Atoms: The common static depictions of atoms can lead students to think that atoms are stationary.
Size and Space: There’s often a misconception that all atoms are of the same size or that there’s no space between atoms in a solid. In reality, atomic size varies, and even in solids, there’s space between particles.
Solid Spherical Atoms: Students might visualize atoms as solid spheres, not realizing that they consist mostly of empty space with a nucleus in the center and electrons orbiting around.
Permanent Molecules: Students might believe that once atoms come together to form a molecule, they are permanently bonded and can’t be separated, not understanding that chemical reactions can break and form bonds.
- Atoms as Miniature Solar Systems: Students sometimes think of atoms as miniature solar systems, with electrons moving in fixed orbits around the nucleus, similar to planets around the sun. The modern understanding is different, with electrons occupying probabilistic orbitals rather than fixed paths.
Shape and Color: Given the colorful models in textbooks, students might assume atoms have specific colors and consistent shapes.
Confusing Atoms and Molecules: Students often use the terms “atom” and “molecule” interchangeably, not realizing that atoms are the basic units of elements, while molecules consist of two or more atoms bonded together.
Properties of Matter
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All clear and colorless liquids are water: Just because a substance is clear and colorless doesn’t mean it’s water. Many other liquids, like ethanol, are also clear and colorless.
If two substances look alike, they must be the same: Two different substances can have similar appearances but very different properties. For example, sugar and salt look similar but taste very different and have different solubilities.
Density is always constant for a given substance: While density can be a characteristic property, it can vary with temperature and pressure for many substances.
Chemical reactions always involve dramatic changes: Some might think that all chemical reactions result in explosions, color changes, or gas production. However, many reactions can be subtle or even undetectable without specific tests.
Pure substances must be in solid form: Pure substances can exist in all states of matter: solid, liquid, gas, and plasma.
Physical changes always involve a change in state: While changes of state (e.g., melting or boiling) are physical changes, other types of physical changes, like dissolving sugar in water, don’t involve a change of state.
All metals are magnetic: While some metals like iron are magnetic, many, like aluminum or copper, are not.
All substances have a unique smell or taste: Not all substances have detectable or unique odors or tastes. Additionally, using taste to identify chemicals can be dangerous.
A substance’s boiling or melting point changes based on the amount present: The boiling or melting point of a substance is a characteristic property and remains consistent regardless of the quantity, as long as external conditions (like pressure) are constant.
All gases are colorless and odorless: While many gases, like oxygen and hydrogen, are colorless and odorless, others like chlorine are not.
All substances react with acid (or any other reagent) in the same way: Different substances can react differently (or not at all) with the same reagent. For instance, while magnesium reacts with hydrochloric acid to produce hydrogen gas, copper does not.
Comparing Densities
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Heavier objects are denser: Many people might think that if an object is heavier, it’s denser. However, density is the ratio of mass to volume. A larger object might have more mass but could be less dense if its volume is significantly greater.
Density is about weight: While weight (or mass) is a component of density, density also considers volume. Two objects with the same weight can have different densities if their volumes are different.
Objects that float in water are always less dense than water: While it’s generally true that objects that float in water are less dense than the water, it’s possible for objects with densities slightly greater than water to float due to surface tension or other factors, especially when the objects are small.
All metals are denser than water: While many metals are denser than water, not all are. For instance, lithium is a metal that’s less dense than water.
Solids are always denser than liquids: While this is often the case, there are exceptions. For example, ice (solid water) is less dense than liquid water, which is why ice floats.
Dense materials feel heavy: A small volume of a dense material, like a tiny piece of lead, might not feel heavy despite its high density.
Changing the shape or size of an object changes its density: The shape or size of an object doesn’t change its density. Crushing a can or expanding a sponge might change its volume and shape, but the material’s density remains the same.
Density is a property of solids only: Density is a property of all states of matter, including liquids, gases, and even plasmas.
Air has no density because it’s invisible: Just because we can’t see air doesn’t mean it lacks density. Air has a measurable density, although it’s much less than most solids and liquids.
Increasing temperature always decreases density: While it’s true for many substances that their density decreases as temperature rises (because they expand), this isn’t universal. Water, for instance, becomes denser as it cools until it reaches about 4°C, after which it becomes less dense as it freezes.
Dense materials are always hard or tough: Material toughness or hardness isn’t directly related to density. Some very dense materials can be soft, and some less dense materials can be tough.
States of Matter
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Only three states of matter: Many people are taught in elementary school that there are three states of matter: solid, liquid, and gas. However, there are more, such as plasma (found in stars and neon signs) and Bose-Einstein condensates (found at extremely low temperatures), among others.
Solids are completely rigid: While solids have a defined shape and volume, not all are completely hard or rigid. Some solids, like clay or rubber, can be deformed easily.
Gases have no mass: Just because gases are less dense than solids or liquids doesn’t mean they lack mass. Air, for instance, has mass and weight, which is why we have atmospheric pressure.
Particles in solids don’t move: Particles in solids do vibrate in place, although they don’t flow or move about freely as in liquids or gases.
All solids melt into liquids: While many solids do melt into liquids when heated, some directly sublimate into a gas, skipping the liquid phase.
Increasing temperature always turns a solid into a liquid: Some substances will decompose or undergo a chemical reaction before melting when heated.
Particles in a gas are far apart and have no interactions: While gas particles are generally farther apart than in solids or liquids, they still collide and can exert forces on each other, especially at high pressures.
Increasing temperature always causes a substance to change to a higher-energy state of matter: While typically true, there are exceptions. For instance, increasing the temperature of solid carbon dioxide (dry ice) causes it to sublimate into a gas, not become a liquid.
Water is the only substance that exists naturally on Earth in all three states: While water is the most familiar substance that can be found as a solid (ice), liquid (water), and gas (water vapor) on Earth, other substances, like carbon dioxide, can also exist in multiple states.
States of matter are permanent characteristics of materials: The state of a substance is dependent on temperature and pressure conditions. For example, oxygen is a gas under standard conditions, but it can be a solid or liquid under different temperatures and pressures.
Plasma is just a hot gas: While plasma and gas have similarities, they are distinct states of matter. In a plasma, atoms have been ionized, meaning electrons are detached from their atoms, leading to a mix of ions and free electrons.
Changing the state of matter is always a physical change: While many state changes, like melting or boiling, are physical changes, some involve chemical changes. For example, when wood burns, it produces ashes, gases, and smoke, all involving chemical transformations.
Heat Transfer
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Cold is transferred: People often think cold can be transferred, like when holding an ice cube. In reality, heat is what’s transferred. When holding an ice cube, heat from your hand is moving to the ice, not the other way around.
Metal is cold: People often think metals are inherently cold because they feel cold to the touch. In reality, metals are good conductors of heat, so they rapidly draw heat away from your skin, making them feel cold.
Thicker clothing is always warmer: While thicker clothing can trap more air, which acts as an insulator, the material’s properties and how tightly it’s woven can also affect its insulative qualities.
Heat rises: It’s commonly said that “heat rises,” but it’s more accurate to say that hot air rises. This is because hot air is less dense than cold air, so it rises due to buoyancy.
Vacuum flasks (like Thermos bottles) have a vacuum to prevent all heat transfer: While the vacuum in these flasks does prevent conduction and convection, it doesn’t prevent radiation. The flask’s reflective lining helps reduce radiant heat transfer.
All materials expand when heated: While most materials expand when heated, there are exceptions, such as water, which contracts when heated from 0°C to 4°C before expanding.
Microwave ovens cook food from the inside out: Microwaves penetrate food but typically only to a depth of a few centimeters. It’s the water molecules in the food absorbing the microwaves and generating heat, which then conducts to the inner portions of the food.
Frozen food items will thaw faster on a wooden or plastic board than on metal: Metal is a good conductor of heat, so frozen items will usually thaw faster when placed on a metal surface than on wood or plastic.
Larger objects always take longer to heat up or cool down: While size can play a role, the material’s properties and the object’s shape can also significantly affect the rate of heat transfer.
Heat and temperature are the same: Heat refers to the energy transferred due to temperature differences, while temperature is a measure of the average kinetic energy of the particles in a substance. It’s possible for two objects to have the same temperature but different amounts of heat (e.g., a cup of water vs. a bathtub of water at the same temperature).
Two objects at the same temperature are in thermal equilibrium, so no heat transfer occurs between them: This is generally true, but if the surrounding conditions change (e.g., one object is exposed to sunlight), heat transfer can still occur.
Thermal Conductors and Insulators
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All metals are equally good conductors: While metals are generally good thermal conductors, there are variations among them. For example, silver is a better conductor than lead.
All non-metals are insulators: Although many non-metals are poor conductors (insulators), there are exceptions, such as graphite (a form of carbon) which is a good conductor.
Thermal and electrical conductivity always go hand in hand: While there’s often a correlation between thermal and electrical conductivity (many good thermal conductors, like copper, are also good electrical conductors), there are exceptions. For instance, diamond is an excellent thermal conductor but a poor electrical conductor.
Insulators do not conduct heat at all: This is a misunderstanding. Insulators are materials that conduct heat poorly compared to conductors. However, given enough time or a high enough temperature difference, heat will still pass through insulators, albeit slowly.
Thicker materials are always better insulators: The thickness of a material can play a role in its insulating capability, but its material properties are more critical. A thin layer of a good insulator might outperform a thicker layer of a poor insulator.
Air is a good conductor because it gets hot in summer: Air is actually a poor conductor (good insulator). The reason it gets hot in summer is due to the sun’s radiation heating the Earth’s surface, which then heats the air above it primarily through convection.
If something feels cold, it’s a good conductor: When an object feels cold (like a metal doorknob in winter), it might indeed be conducting heat away from your hand efficiently. However, the sensation of coldness is about the rate of heat transfer, not the absolute temperature of the object.
Insulators keep things warm: Insulators don’t “keep things warm.” They slow down the rate of heat transfer. For instance, a thermos bottle reduces the rate at which heat is lost from hot liquid inside it to the outside environment.
Good conductors always feel cold: The sensation of cold or warmth when touching an object depends on its temperature relative to your body and how quickly it can transfer heat. A good conductor at body temperature would not feel cold.
Wood is a good insulator, so wooden spoons should not get hot in boiling water: While wood is a poor conductor compared to metals, it can still conduct heat. A wooden spoon left in boiling water will eventually get hot, although it might take longer than a metal spoon.
Materials are either conductors or insulators: In reality, conductivity exists on a spectrum, with some materials being very good conductors, some being very good insulators, and many lying somewhere in between.
Physical and Chemical Changes
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All changes that involve heat are chemical changes: Just because heat is involved doesn’t mean a substance has chemically changed. For instance, melting ice is a physical change even though it requires heat.
Any change in color indicates a chemical change: While color change can be an indication of a chemical change, it can also occur with physical changes. For example, changing the thickness or particle size of a material can change its color.
All dissolving processes are physical changes: While dissolving common salt (sodium chloride) in water is a physical change, dissolving zinc in hydrochloric acid is a chemical change as it produces hydrogen gas and zinc chloride.
If a gas is produced, it’s always a chemical change: While many chemical reactions produce gases, some physical processes, like boiling, also produce gas (steam in the case of boiling water).
Physical changes are always reversible, and chemical changes are not: Many physical changes are reversible, like freezing and melting. However, some, like breaking a glass, are not easily reversible. Similarly, some chemical changes can be reversed under the right conditions.
Changes that are fast are always chemical: The speed of a change doesn’t determine its type. Rapid freezing or boiling is a fast physical change, while some chemical reactions can take a long time.
Physical changes only involve phase changes: While phase changes (like boiling, freezing, etc.) are physical changes, other types of physical changes exist, like tearing paper or grinding crystals to powder.
Chemical changes alter the mass of substances: The law of conservation of mass states that matter is neither created nor destroyed in a chemical reaction. While the substances may change, the total mass remains the same (assuming a closed system).