CUA 1 review

An __________ is a pure substance made of only one kind of atom.

• element

• compound

• mixture

• solution

Answer explanation

An element is a pure substance consisting of only one type of atom, making it the correct answer. Compounds are made of two or more different atoms, while mixtures and solutions contain multiple substances.

A __________ is a substance made of two or more elements chemically combined.

• compound

• mixture

• atom

• solution

Answer explanation

A compound is defined as a substance formed when two or more elements chemically combine. Unlike mixtures or solutions, compounds have a fixed composition and distinct properties, making 'compound' the correct answer.

A __________ is two or more atoms bonded together.

• molecule

• element

• compound

• ion

Answer explanation

A molecule is defined as two or more atoms bonded together. While an element consists of a single type of atom and a compound is a type of molecule made from different elements, the correct term for bonded atoms is molecule.

Tags

NGSS.MS-PS1-1

The chemical formula shows the types of __________ and the number of __________ in a compound.

• atoms, atoms

• molecules, molecules

• elements, compounds

• ions, electrons

Answer explanation

The chemical formula indicates the types of atoms and the number of atoms in a compound. Therefore, the correct choice is 'atoms, atoms', as it accurately describes the components of a chemical formula.

Tags

NGSS.MS-PS1-1

The small numbers in a chemical formula (like the 2 in H₂O) are called __________.

• subscripts

• coefficients

• superscripts

• isotopes

Answer explanation

The small numbers in a chemical formula, like the 2 in H₂O, indicate the number of atoms of each element in the compound. These are called subscripts, distinguishing them from coefficients, which indicate the number of molecules.

The large number in front of a chemical formula (like the 3 in 3H₂O) is called a __________.

• coefficient

• subscript

• reactant

• product

Answer explanation

The large number in front of a chemical formula, like the 3 in 3H₂O, is called a coefficient. It indicates how many molecules of that substance are present, distinguishing it from subscripts, which show the number of atoms in a molecule.

________ are always made up of different elements.

• Compounds

• Elements

• Mixtures

• Atoms

Answer explanation

Compounds are substances formed when two or more different elements chemically combine. Unlike elements, which consist of only one type of atom, compounds always contain multiple elements in fixed ratios.

Label each as Element, Molecule of an element, or Compound: O₂ → __________ H₂O → __________ NaCl → __________ Fe → __________

• O₂ → Molecule of an element H₂O → Compound NaCl → Compound Fe → Element

• O₂ → Element H₂O → Molecule of an element NaCl → Compound Fe → Compound

• O₂ → Compound H₂O → Element NaCl → Molecule of an element Fe → Compound

• O₂ → Compound H₂O → Compound NaCl → Element Fe → Molecule of an element

Answer explanation

O₂ is a molecule of an element (two oxygen atoms), H₂O and NaCl are compounds (composed of different elements), and Fe is an element (a single type of atom). Thus, the correct labeling is: O₂ → Molecule of an element, H₂O → Compound, NaCl → Compound, Fe → Element.

Tags

NGSS.MS-PS1-1

O₂ is considered a molecule of an element, while H₂O is considered a compound because:

• O₂ contains only one type of atom, while H₂O contains different types of atoms.

• Both O₂ and H₂O contain only one type of atom.

• H₂O is a molecule of an element, and O₂ is a compound.

• O₂ contains different types of atoms, while H₂O contains only one type of atom.

Answer explanation

O₂ is a molecule made up of two oxygen atoms, which are the same type, making it a molecule of an element. In contrast, H₂O consists of different types of atoms (hydrogen and oxygen), classifying it as a compound.

Tags

NGSS.MS-PS1-1

Which of the following correctly represents a model of O₂ and a model of H₂O with labeled atoms?

• A model showing two oxygen atoms bonded together for O₂, and two hydrogen atoms bonded to one oxygen atom for H₂O, with each atom labeled.

• A model showing two hydrogen atoms bonded together for O₂, and two oxygen atoms bonded to one hydrogen atom for H₂O, with each atom labeled.

• A model showing one oxygen atom and one hydrogen atom bonded for O₂, and three hydrogen atoms bonded to one oxygen atom for H₂O, with each atom labeled.

• A model showing three oxygen atoms bonded together for O₂, and one hydrogen atom bonded to one oxygen atom for H₂O, with each atom labeled.

Answer explanation

The correct model for O₂ shows two oxygen atoms bonded together, while H₂O consists of two hydrogen atoms bonded to one oxygen atom. This accurately represents the molecular structures of both compounds.

Tags

NGSS.MS-PS1-1