Final answer:
To classify substances, we identify them as pure elements, pure compounds, or mixtures. Pure elements consist of one type of atom, while pure compounds are made up of two or more atoms bonded chemically. Mixtures are combinations of elements or compounds that do not involve chemical bonding.
Step-by-step explanation:
To classify each image as showing a pure element, a pure compound, a mixture of two elements, or a mixture of an element and a compound, we need to know the definitions of each category:
- A pure element is a substance that consists of only one type of atom.
- A pure compound is a substance made from two or more different elements that are chemically combined in a fixed ratio.
- A mixture of two elements is when they are combined without forming a new chemical substance, and the elements can be physically separated.
- A mixture of an element and a compound contains both an uncombined pure element and a compound.
Examples include:
- Salt (NaCl) - Pure compound because it is composed of sodium (Na) and chlorine (Cl) atoms chemically bonded in a 1:1 ratio.
- Pure water (H2O) - Pure compound because it consists of hydrogen and oxygen atoms bonded in a 2:1 ratio.
- Soil - Heterogeneous mixture as it has a non-uniform composition of organic matter, minerals, gases, liquids, and organisms.
- Salt water - Homogeneous mixture as the salt is evenly distributed throughout the water.
- Pure air - Homogeneous mixture of various gases such as nitrogen, oxygen, and small amounts of other gases.
- Carbon dioxide (CO2) - Pure compound due to the chemical combination of carbon and oxygen in a fixed proportion.
- Gold (Au) - Pure element because it consists only of gold atoms.
- Bronze - Mixture of the elements copper and tin as well as additional elements like aluminum or nickel.
When determining the classification, consider whether the substance has a uniform composition (homogeneous) or varies (heterogeneous), and whether it is a pure substance or a mixture.