TCI Gr 7. Lesson 2 Review

Zoe, Ethan, and Jackson are curious about molecules! Why do scientists use models to portray molecules?

• Scientists have no other way to see molecules.

• It is the only way they can provide proof for their work.

• It makes important aspects of the molecule easier to see.

• It is the only way they can figure out how to combine atoms.

Emma, Abigail, and Grace are having a debate about molecules. What determines a molecule's atomic composition?

• the weight of the molecules and their properties

• the size of the molecule and its place on the periodic table

• the types of elements and number of atoms in each element

• the number of atoms in each element and the size of the molecule

Aria, Elijah, and James are having a debate about diamonds. Aria claims that a diamond is a crystal that:

• is made of one element.

• is made of multiple elements.

• extends forever.

• has a spherical structure.

Ava, Avery, and Liam are having a debate. Ava thinks that water (H₂O) and hydrogen peroxide (H₂O₂) are different because they have different structures. Avery believes it's because hydrogen peroxide has one more oxygen atom than water. Liam, on the other hand, thinks they have different compositions. Who do you think is correct?

• Ava: The only difference is that they have different structures.

• Avery: Hydrogen peroxide has one more oxygen atom than water.

• Liam: The only difference is that they have different compositions.

• None of them: Atoms in water have stronger bonds than atoms in hydrogen peroxide.

Grace, Henry, and William were having a debate. Grace thinks graphite is a good writing tool because it has hexagonal sheets which are weakly connected to each other, whereas diamond is not because it has a strong cubic structure. Henry and William have different opinions. Who do you think is correct?

• Grace is correct. Graphite has hexagonal sheets which are weakly connected to each other, whereas diamond has a strong cubic structure.

• Henry is correct. Graphite has hexagonal sheets which are strongly connected to each other, whereas diamond has a weak cubic structure.

• William is correct. Graphite has a weak cubic structure, whereas diamond has hexagonal sheets which are strongly connected to each other.

• None of them are correct. Graphite has a strong cubic structure, whereas diamond has hexagonal sheets which are weakly connected to each other.

Grace, Noah, and David were having a snowball fight when they noticed something interesting about the snowflakes. Can you guess why the snowflakes they were throwing had a hexagonal shape?

• There are six atoms in a water molecule.

• Crystals typically form in repeating patterns of six.

• It is very difficult for a liquid to freeze into any other structure.

• Their atomic-level structure is made up of crystals with six sides.

Arjun, Avery, and Evelyn are having a debate about the composition of water. They all agree that water is made up of hydrogen and oxygen atoms, but they disagree on the exact ratio. Can you help them figure out the correct composition of water?

• two hydrogen atoms and one oxygen atom.

• four hydrogen atoms and six oxygen atoms.

• one hydrogen atom and three oxygen atoms.

• eight hydrogen atoms and ten oxygen atoms.

During a chemistry class, Liam, Samuel, and Aria were discussing the properties of various molecules. They came across nitrous oxide (also known as "laughing gas") used in dental offices and noticed that it has very different properties from nitrogen monoxide (NO) and nitrogen dioxide (NO₂). Here's a ball-and-stick model of nitrous oxide (N₂O) for reference.

Which statement best explains why nitrous oxide (N₂O) has very different properties from nitrogen monoxide (NO) and nitrogen dioxide (NO₂)?

• They all have different chemical bonds.

• They all have different arrangements of atoms.

• They are all composed of different types of atoms.

• They are all composed of different ratios of atoms.

Noah, Arjun, and Lily are having a friendly debate about sugar and salt crystals. They know that crystals are repeated patterns built up out of subunits. Noah points out that salt crystals have 90-degree angles between the sides, while Lily shows that sugar crystals have different angles. Arjun is curious about the reason behind this difference.

Which of the following best explains the differences in shape between sugar and salt crystals?

• Both types of molecules form different angles at random.

• The subunits of sugar molecules and salt molecules are different shapes.

• Sugar comes from living organisms and salt comes from non-living sources.

• Manufacturers make the crystals that way to tell them apart in the factory.

Ethan, Mason, and Abigail are having a debate about pencils. They wonder why graphite is a good writing tool, whereas diamond is not. Can you help them figure it out?

• Graphite has hexagonal sheets which are weakly connected to each other, whereas diamond has a strong cubic structure.

• Graphite has hexagonal sheets which are strongly connected to each other, whereas diamond has a weak cubic structure.

• Graphite has a weak cubic structure, whereas diamond has hexagonal sheets which are strongly connected to each other.

• Graphite has a strong cubic structure, whereas diamond has hexagonal sheets which are weakly connected to each other.