Understanding Molecules and Compounds

Which of the following best describes a molecule?

• A very large crystal of an element

• A group of two or more atoms bonded together

• A single type of atom

• A substance that cannot be seen even under a microscope

Which of the following is made of only one kind of atom?

• Salt

• Water

• Oxygen gas

• Carbon dioxide

Which of these is not a molecule?

• O₂

• CO₂

• H

• H₂O

What do the atoms in a molecule do?

• Fight each other

• Randomly roll around

• Stay loosely attached

• Share or exchange electrons to stay together

Which of these substances is a compound?

• Iron

• Hydrogen gas

• Water

• Gold

What happens to atoms during a chemical reaction?

• They disappear

• They break apart into light

• They rearrange to form new substances

• They melt into liquids

Which of the following correctly shows a molecule of a compound?

• O₂

• H₂

• CO₂

• Fe

What is common among all elements?

• They are all gases

• They are made up of only one kind of atom

• They can only be found in nature

• They always exist as solids

Why can’t elements be broken into simpler substances?

• Because they are unbreakable

• They are the simplest form of matter

• They are protected by molecules

• Because they are too small

If a substance is made of two types of atoms joined together, it is a:

• Molecule of an element

• Mixture

• Compound

• Crystal