2.3 Elements and Compounds

Essential Question: What are elements and compounds?

• Elements are pure substances consisting of only one type of atom, while compounds are substances formed from two or more elements chemically bonded together.

• Elements and compounds are the same and can be used interchangeably.

• Elements are mixtures of different substances, while compounds are pure substances.

• Elements are always gases, while compounds are always solids.

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Pure substances can be classified as:

• elements and compounds

• mixtures and solutions

• solids and liquids

• gases and vapors

What does the periodic table list?

• Elements

• Planets

• Mathematical formulas

• Historical events

Which laws do students use to analyze compounds based on the mass of component elements?

• Law of Conservation of Mass

• Law of Definite Proportions

• Law of Multiple Proportions

• All of the above

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Compounds are made up of:

• Atoms

• Molecules

• Elements

• Mixtures

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An element is a substance that consists of how many types of atoms?

• One type of atom

• Two types of atoms

• Three types of atoms

• Four types of atoms

The periodic table is:

• a chart of the elements arranged according to their atomic number

• a list of chemical reactions

• a table of physical constants

• a calendar of periodic events

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A compound is a substance formed when two or more chemical elements are chemically bonded together. Which of the following is an example of a compound?

• Oxygen (O2)

• Water (H2O)

• Gold (Au)

• Iron (Fe)

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The law of definite proportions states that a chemical compound always contains exactly the same proportion of elements by mass.

• A chemical compound always contains the same proportion of elements by mass.

• A chemical compound can contain varying proportions of elements by mass.

• The proportion of elements in a compound changes with temperature.

• The proportion of elements in a compound changes with pressure.

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Percent by mass means:

• the ratio of the mass of a solute to the total mass of the solution, multiplied by 100

• the ratio of the volume of a solute to the total volume of the solution, multiplied by 100

• the ratio of the number of moles of a solute to the total number of moles of the solution, multiplied by 100

• the ratio of the mass of a solute to the mass of the solvent, multiplied by 100