Topic 4b: Atoms vs. Molecules and Pure Substances

Match the following terms with their definitions.

• A combination of different substances that remain physically separate.

• Atom

• The smallest particle of matter that cannot be divided further.

• Molecule

• A group of atoms bonded together, representing the smallest fundamental unit of a chemical compound.

• Mixture

• A substance formed when two or more chemical elements are chemically bonded together.

• Compound

Answer explanation

The smallest particle of matter that cannot be divided further is an atom. Atoms are the basic building blocks of matter, while molecules and compounds are made up of atoms, and mixtures consist of multiple substances.

Which of the following is an example of an element?

• Water

• Helium

• Carbon dioxide

• Saltwater

Answer explanation

Helium is an element, represented by the symbol He on the periodic table. In contrast, water, carbon dioxide, and saltwater are compounds or mixtures, not elements.

A molecule is:

• A single atom

• A group of atoms bonded together

• An atom of only one element

• A mixture of elements and compounds

Answer explanation

A molecule is defined as a group of atoms bonded together, forming the smallest unit of a chemical compound. This distinguishes it from a single atom or a mixture, making 'a group of atoms bonded together' the correct choice.

Match the following descriptions with the correct terms.

• Sand and salt, or air

• A mixture of different substances

• O2, N2, or H2

• A combination of atoms of different elements bonded together

• H2O, CO2, or NaCl

• A single atom of one element

• Helium, Neon, or Argon

• Made of two or more atoms of the same element

Answer explanation

A compound is defined as a combination of atoms of different elements bonded together, distinguishing it from elements and mixtures. Therefore, the correct choice is 'A combination of atoms of different elements bonded together'.

Match the following descriptions with the correct type of substance.

• A substance formed when two or more chemical elements are chemically bonded together.

• Atom

• The smallest unit of a chemical element, consisting of a nucleus and electrons.

• Element

• A pure substance consisting of only one type of atom.

• Compound

• A combination of two or more substances that are not chemically bonded.

• Mixture

Answer explanation

Water (H₂O) is a compound because it consists of two different elements, hydrogen and oxygen, chemically bonded together in a fixed ratio. It is not an element, mixture, or atom.

Which of the following is a pure substance?

• Air

• Saltwater

• Baking soda

• Sand

Answer explanation

Baking soda is a pure substance because it consists of only one type of particle, sodium bicarbonate. In contrast, air, saltwater, and sand are mixtures containing multiple components.

An atom is the smallest unit of an _________.

Answer explanation

An atom is the smallest unit of an element, which is a pure substance consisting of only one type of atom. Therefore, the correct answer is 'element'.

A _________ is made of two or more atoms bonded together.

Answer explanation

A molecule is defined as a group of two or more atoms bonded together, making it the correct answer to the question. Other terms do not accurately describe this specific arrangement of atoms.

An element is a pure substance made of only one type of _________.

Answer explanation

An element is defined as a pure substance consisting of only one type of atom. This means that all atoms in an element are identical, distinguishing it from compounds, which are made of different types of atoms.

A compound is a molecule made of two or more different _________ bonded together.

Answer explanation

A compound is defined as a molecule made of two or more different elements bonded together. Therefore, the correct answer to fill in the blank is 'elements'.