Chemistry: Atoms, Molecules, and Compounds: Building Blocks Worksheet

Question 1

Define an atom in your own words. Include one example of an atom.

Accepted Answer

An atom is the smallest basic unit of an element that still has the properties of that element. One example is a carbon atom.

Question 2

Define a molecule in your own words. Include one example of a molecule.

Accepted Answer

A molecule is a group of two or more atoms bonded together. One example is an oxygen molecule, O2, which has two oxygen atoms bonded together.

Question 3

A water particle has the formula H2O. How many hydrogen atoms and oxygen atoms are in one water molecule?

Accepted Answer

One water molecule has 2 hydrogen atoms and 1 oxygen atom. The small 2 after H means there are two hydrogen atoms, and O without a number means there is one oxygen atom.

Question 4

Classify each substance as an element, a molecule, or a compound: O2, NaCl, and He. Explain your choices.

Accepted Answer

O2 is a molecule because it has two oxygen atoms bonded together. NaCl is a compound because it has atoms of two different elements, sodium and chlorine, bonded together. He is an element because it is made of only helium atoms.

Question 5

Look at the formula CO2. What elements are present, and how many atoms of each element are in one molecule of CO2?

Accepted Answer

CO2 contains carbon and oxygen. One molecule of CO2 has 1 carbon atom and 2 oxygen atoms.

Question 6

Explain the difference between an element and a compound using the examples oxygen gas, O2, and water, H2O.

Accepted Answer

An element is made of only one kind of atom, so oxygen gas, O2, is an element even though it is a molecule. A compound is made of two or more different elements chemically bonded together, so water, H2O, is a compound.

Question 7

A student says, "All molecules are compounds." Is the student correct? Explain using an example.

Accepted Answer

The student is not correct. Some molecules, such as O2, are made of only one element, so they are molecules but not compounds.

Question 8

Count the total number of atoms in one molecule of glucose, C6H12O6. Show how you counted.

Accepted Answer

One molecule of glucose has 24 total atoms. It has 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms, and 6 + 12 + 6 = 24.

Question 9

A diagram shows three particles. Particle A is one single oxygen atom. Particle B is two oxygen atoms bonded together. Particle C is one carbon atom bonded to two oxygen atoms. Identify each as an atom, molecule, element, or compound. Use all labels that apply.

Accepted Answer

Particle A is an atom and an element because it is one oxygen atom. Particle B is a molecule and an element because it has two oxygen atoms bonded together. Particle C is a molecule and a compound because it has carbon and oxygen atoms bonded together.

Question 10

The formula for table salt is NaCl. What does this formula tell you about the types of atoms in table salt?

Accepted Answer

The formula NaCl tells us that table salt contains sodium atoms and chlorine atoms. Because it has two different elements chemically combined, it is a compound.

Question 11

Methane has the formula CH4. Draw or describe the atoms in one methane molecule.

Accepted Answer

One methane molecule has 1 carbon atom and 4 hydrogen atoms. A good description is one carbon atom bonded to four hydrogen atoms.

Question 12

Sort these formulas into two groups: elements and compounds. Formulas: N2, H2O, Fe, CO, Cl2, and MgO. Explain your sorting.

Accepted Answer

The elements are N2, Fe, and Cl2 because each contains only one type of element. The compounds are H2O, CO, and MgO because each contains two different elements chemically combined.

Chemistry: Atoms, Molecules, and Compounds: Building Blocks

More Chemistry Worksheets

More Grade 6-8 Worksheets