Periodic Table: Phases (Simplified) - Online Tutor, Practice Problems & Exam Prep

At standard room temperature (25°C) and pressure (1 atm), elements can exist as solids, liquids, or gases. Solids maintain a fixed shape and volume due to tightly packed molecules. Liquids conform to the shape of their container but not the volume, as their molecules are close yet mobile. Gases assume both the shape and volume of their container, with molecules far apart. Most elements are solids, with only mercury and bromine as liquids, while gases include hydrogen, nitrogen, oxygen, and noble gases. Some synthetic elements are unstable and their states are unpredictable.

Periodic Table: Phases (Simplified) Concept 1

Hey everyone. So as we explore the periodic table and its elements, realize that at standard room temperature, which is approximately 25 degrees Celsius, and standard pressure, which is 1 atmosphere, the elements can exist under 3 states of matter. So we have our solids, our liquids, and our gases. Now if we take a look at these 3 states of matter a little bit more closely, we can talk about how their molecules orient themselves. For solids, they're kind of locked or frozen in place, and they're in direct contact with one another and because of that, they don't really conform to their container. As a result of this, we say that solids maintain a fixed shape and volume. Okay. So they're kind of frozen in place the way they are. Next, we have liquids. For liquids, the molecules are in close proximity to each other but they're able to move around more freely. So they're moving around one another, and because of this orientation, we can say that liquids can conform to the shape of the container, but not necessarily the volume of the container. So think about it like this—let's say we have a container that is 25 mL large, but we only have 10 mL of liquid. The liquid itself can conform to the shape of the container, but, try as it might, because there's not enough liquid, it can't fill up the entire volume of the container. So this is what happens with liquids. Gases, on the other hand, because their molecules are so far apart from each other, this opens up new properties or expanded properties when compared to solids and liquids. We won't talk about them here, but just realize because the molecules are further apart within gaseous states of matter, we can say that because of this, they assume both the shape and volume of the container.

Now if we take a look at the periodic table, we can see that a vast majority of the elements themselves are in solid form, like lithium, zinc, or sulfur. Some of them, very few of them, are in the form of gases. So, we can see that with hydrogen, nitrogen, oxygen, and chlorine; and the last batch is easy to remember because they're part of group 8A, which are our noble gases. So it's in the name; they're gases. And then finally, we can see that the rarest form is our liquids. Under standard room temperature and pressure, there are only 2 elements that exist in liquid form, and that will be mercury and bromine. Now you might also see that some elements are not color-coded as solids, liquids, or gases. We find those in the 7th row from Rf to Og. These elements are synthetically made within laboratories, and because they have such high masses, they're very unstable. So even at standard temperature and pressure, it's hard for us to determine what state they exist in. So they're very unpredictable. So for that reason, we don't give them any state of matter at 25 degrees Celsius or 1 atmosphere. So just remember that based on these different types of temperatures and pressures, a certain state of matter is preferred by different elements.

Periodic Table: Phases (Simplified) Example 1

So in this example question, it says, identify the element that is a representative element that is not diatomic in the second period that assumes the shape and volume of the container that it is in. So there's a lot of information being thrown at us right now. First, we're going to say it is a representative element. Remember, representative elements is just one of the large categories for the elements of the periodic table. If you're a representative element, that means you cannot be a transition metal. Unfortunately, all of these choices are representative elements. None of them are transition metals. So that part's not going to help us. Well, next, it is not diatomic. Here, beryllium is monoatomic, silicon is monoatomic, boron is monoatomic, neon and argon. So that also is not going to help us too much. Now, they're getting to some important stuff. They're saying second period. So second period means that in the 2nd row of the periodic table, and they say that it assumes the shape and volume of the container that it is in. So if it assumes both shape and volume, that means that it is a gas. So basically, this question is asking us to find an element that's in the 2nd row of the periodic table and is also a gas. So come up here, we're going to say, the 2nd row is here, and the only ones that are gases are nitrogen, oxygen, fluorine, and neon. But out of those four, neon is the only one that's given to us as a choice. So that would mean that option d would be our correct answer. So everything we've been learning about the periodic table, it adds on top of one another. You got to remember representative elements versus transition metals. You have to remember phases. You have to remember elemental forms. This is the key to getting the type of question like this correct. So again, the only thing that fits all of these descriptions perfectly would be option d, neon.

Which of the following elements is a nonmetal that is a polyatomic solid?

• A. Carbon
• B. Oxygen
• C. Sulfur
• D. Radon
• E. Cesium

Which of the following exists as a diatomic solid at room temperature?

• A. Bromine
• B. Tellurium
• C. Sulfur
• D. Chlorine
• E. Iodine

Here’s what students ask on this topic:

What are the states of matter for elements at standard room temperature and pressure?

At standard room temperature (25°C) and pressure (1 atm), elements can exist in three states of matter: solids, liquids, and gases. Solids have tightly packed molecules, maintaining a fixed shape and volume. Examples include lithium, zinc, and sulfur. Liquids have molecules that are close but can move around, conforming to the shape but not the volume of their container. Mercury and bromine are the only elements in liquid form under these conditions. Gases have molecules far apart, allowing them to assume both the shape and volume of their container. Examples include hydrogen, nitrogen, oxygen, and noble gases like helium and neon.

Why do most elements exist as solids at room temperature?

Most elements exist as solids at room temperature because their molecules are tightly packed together, which allows them to maintain a fixed shape and volume. This close packing is due to strong intermolecular forces that hold the molecules in place. As a result, solids do not conform to the shape or volume of their container. Examples of solid elements include lithium, zinc, and sulfur. The stability and low kinetic energy at room temperature favor the solid state for the majority of elements on the periodic table.

Which elements are liquids at standard room temperature and pressure?

At standard room temperature (25°C) and pressure (1 atm), only two elements exist in liquid form: mercury (Hg) and bromine (Br). Mercury is a metal, and its liquid state is due to its unique electron configuration, which weakens the metallic bonds. Bromine is a halogen, and its liquid state is due to relatively weak intermolecular forces compared to other halogens. These properties allow both elements to remain in the liquid state under standard conditions.

What are the characteristics of gases at room temperature and pressure?

Gases at room temperature and pressure have molecules that are far apart, allowing them to move freely. This results in gases assuming both the shape and volume of their container. The low density and high kinetic energy of gas molecules contribute to their ability to expand and fill any available space. Examples of gaseous elements include hydrogen (H₂), nitrogen (N₂), oxygen (O₂), and noble gases like helium (He) and neon (Ne).

Why are some elements on the periodic table not assigned a state of matter at room temperature?

Some elements, particularly those in the 7th row of the periodic table (from Rutherfordium, Rf, to Oganesson, Og), are synthetically made in laboratories and have very high atomic masses. These elements are highly unstable and have short half-lives, making it difficult to determine their state of matter at standard room temperature and pressure. Their instability and rapid decay prevent scientists from accurately assigning them a solid, liquid, or gas state under these conditions.