A sealed jar holds particles that are all alike. Every particle is a single atom, and all of the atoms are the same kind. How is the contents of the jar best classified?

In a sealed tube every particle is identical, and each one is a single carbon atom joined to two oxygen atoms. How is the contents of the tube best classified?

A gas cylinder holds two kinds of particle spread evenly everywhere: single argon atoms and pairs of joined nitrogen atoms. No argon atom is joined to a nitrogen atom. How is the gas best classified?

A model of a sample shows clumps of one kind of particle packed in one corner and a different kind of particle filling the rest, with none of them joined. How is the sample best classified?

A tank contains one kind of particle only. Each particle is two oxygen atoms bonded together. How is the contents of the tank best classified?

In a beaker every particle is the same: one sodium atom bonded to one chlorine atom. The particles are packed evenly through the sample. How is the sample best classified?

A magnified model of a metal bar shows nothing but gold atoms packed together, with no atom of any other element anywhere in the bar. How is the bar best classified?

A diagram of a liquid shows water molecules with sugar molecules scattered evenly between them. No sugar molecule is bonded to a water molecule. How is the liquid best classified?

A diagram shows large grains, each of many silicon and oxygen atoms bonded together, resting in patches at the bottom of a container of water molecules. How is the container's contents best classified?

A sample contains only one kind of atom, but those atoms are bonded together in pairs. Which reasoning about the sample is correct?

In a compound, every particle contains atoms of more than one element chemically joined together.

A student builds a bead model of a compound. Which arrangement of beads should the model show?

Models A and B both show copper and zinc atoms, none bonded. In A the atoms are mixed evenly, and in B each kind sits in its own patches. How are the samples best classified?

A sealed flask holds one kind of particle only: each is one nitrogen atom bonded to three hydrogen atoms. What is in the flask?

Salt is stirred into water until it disappears. The liquid is clear, tastes salty at the top and the bottom, and looks the same everywhere. How is the liquid best classified?

A polished slab of granite shows pink, white and black grains, and each kind of grain can be chipped out separately. How is the granite best classified?

A wire is drawn from a bar of pure copper. Every part of the bar is copper, and no chemical change can break it down into anything simpler. How is the wire best classified?

Dry air sampled at the floor and at the ceiling of a sealed room has the same amounts of nitrogen, oxygen and argon, and each gas keeps its own behavior. How is the air best classified?

A jar of pure table salt has crystals that are all the same substance. Nothing is left behind when it dissolves, and only a chemical change splits it into sodium and chlorine. How is it classified?

A stainless steel spoon looks the same all over. Under a microscope its iron, chromium and nickel atoms are blended evenly and are not chemically joined. How is the steel best classified?

A dish holds a mix of sand and table salt. Which method separates them so that both are recovered unchanged?

A party balloon is filled from a cylinder of helium. The gas inside is made of single helium atoms and nothing else. How is the gas in the balloon best classified?

Pond water stands in a jar overnight. By morning brown silt lies at the bottom and clearer water sits above it, and the silt can be poured off separately. How is the pond water best classified?

Every mixture looks exactly the same in every part of the sample.

A bottle is labeled with the formula H2SO4. How many different elements are joined in one particle of this substance, and how many atoms does that particle contain in total?

Ozone in the upper atmosphere has the formula O3. How is ozone best classified?

Glucose has the formula C6H12O6. How many atoms in total are joined in one particle of glucose?

Milk of magnesia contains a substance with the formula Mg(OH)2. How many oxygen atoms are in one particle of this substance?

A water treatment plant uses a substance with the formula Al2(SO4)3. How many oxygen atoms are in one particle of it?

Baking soda has the formula NaHCO3. How many different elements are joined in one particle of baking soda?

Rust on an old gate contains a substance with the formula Fe2O3. What does this formula tell you about one particle of that substance?

One gas cylinder is labeled N2 and another is labeled NO. Which cylinder holds a compound, and for what reason?

Clear salt water is boiled in an evaporating dish. The liquid disappears as steam and dry white salt is left in the dish, tasting exactly as it did before. What does this result show?

Electricity is passed through water in a beaker for several minutes. Bubbles of two different gases collect, and nothing like either gas was there before. What does this show about the water?

A spot of black ink is placed near the bottom of paper standing in water. As the water climbs, the spot spreads into blue, red and yellow bands. What does this result show about the ink?

Iron filings and sulfur powder are stirred in a dish, then heated strongly. The gray solid that forms is not pulled out by a magnet at all. What does the heating show?

Iron filings are stirred into a dish of dry sand. Which method separates the iron filings from the sand, leaving both unchanged?

Sodium is a soft metal that reacts violently with water, and chlorine is a choking green gas, yet table salt made from them is a safe white solid. What does this show about a compound?

The substances in a mixture can be separated by physical methods such as filtering, evaporating or using a magnet.

Each element has its own box on the periodic table, but compounds such as water do not.