In addition, many of the simple covalent oxides of the nonmetals are gases, such as CO, CO 2, NO, NO 2, SO 2, SO 3, and ClO 2. Gaseous substances include many binary hydrides, such as the hydrogen halides (HX) hydrides of the chalcogens hydrides of the group 15 elements N, P, and As hydrides of the group 14 elements C, Si, and Ge and diborane (B 2H 6). Many of the elements and compounds we have encountered so far are typically found as gases some of the more common ones are listed in Table 10.1.2. The noble gases and mercury occur as monatomic species, whereas all other gases and bromine are diatomic molecules. The rest of the elements are all solids under normal conditions.įigure 10.1.2 Elements That Occur Naturally as Gases, Liquids, and Solids at 25☌ and 1 atm Gallium (Ga), which melts at only 29.76☌, can be converted to a liquid simply by holding a container of it in your hand or keeping it in a non-air-conditioned room on a hot summer day. In contrast, bromine (as Br 2) and mercury (Hg) are liquids under normal conditions (25☌ and 1.0 atm, commonly referred to as “room temperature and pressure”). Oxygen can also form a second allotrope, the highly reactive triatomic molecule ozone (O 3), which is also a gas. Of these, all the noble gases (group 18) are monatomic gases, whereas the other gaseous elements are diatomic molecules (H 2, N 2, O 2, F 2, and Cl 2). Except for hydrogen, the elements that occur naturally as gases are on the right side of the periodic table. In contrast, the macroscopic properties of a substance depend strongly on its physical state, which is determined by intermolecular forces and conditions such as temperature and pressure.įigure 10.1.2 shows the locations in the periodic table of those elements that are commonly found in the gaseous, liquid, and solid states. The geometric structure and the physical and chemical properties of atoms, ions, and molecules usually do not depend on their physical state the individual water molecules in ice, liquid water, and steam, for example, are all identical. Table 10.1.1 Properties of Water at 1.0 atm Temperature The properties of the three states of water are summarized in Table 10.1.1 Steam is used to drive large machinery, including turbines that generate electricity. Water vapor at temperatures greater than 100☌ is called steam. is a component of the air we breathe, and it is produced whenever we heat water for cooking food or making coffee or tea. Nitrogen (N 2) and oxygen (O 2) are thus referred to as gases, but gaseous water in the atmosphere is called water vapor. Water vapor The distinction between a gas and a vapor is subtle: the term vapor refers to the gaseous form of a substance that is a liquid or a solid under normal conditions (25☌, 1.0 atm). When the temperature is cold enough to transform the liquid to ice, we can ski or skate on it, pack it into a snowball or snow cone, and even build dwellings with it. Under most conditions, we encounter water as the liquid that is essential for life we drink it, cook with it, and bathe in it. For example, H 2O is commonly found in all three states: solid ice, liquid water, and water vapor (its gaseous form). The state of a given substance depends strongly on conditions. (c) Gaseous O 2 fills its container completely-regardless of the container’s size or shape-and consists of widely separated molecules. (b) Liquid O 2 conforms to the shape of its container but has a fixed volume it contains relatively densely packed molecules. (a) Solid O 2 has a fixed volume and shape, and the molecules are packed tightly together. \( \newcommand\)įigure 10.1.1 A Diatomic Substance (O 2) in the Solid, Liquid, and Gaseous States
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