8. Thermochemistry
Formation Equations
Struggling with General Chemistry?
Join thousands of students who trust us to help them ace their exams!Watch the first video
Video duration:
2mRelated Videos
Related Practice
Skip to main content
Realize that elements of the periodic table exist in different standard states or sometimes called natural states when it comes to the natural world. We're going to say here at room temperature, which is approximately 25 degrees Celsius, and standard pressure, which is approximately 1 atmosphere, elements exist as either solids, liquids, or gases. So for a quick review on the periodic table, what we have here in red are the elements that exist as gases. Now, some of them are monoatomic in terms of the noble gases, from helium all the way down to radon. But other gases exist in a diatomic form where there are 2 of them combined together. This includes hydrogen, which is h 2, nitrogen, which is n 2, oxygen, which is o 2, f 2 for fluorine, and c l 2 for chlorine. Then we have a few elements that can exist in the liquid phase. This includes bromine, which is also diatomic, and mercury, which is monoatomic. A vast majority of the other elements on the periodic table in their natural state or standard states exist in the solid form as monoatomic. And then here we have in the bottom row, these that aren't solids, liquids, or gases. These have been formed within laboratory or because of their high atomic masses are very unstable. So they they don't come along with a phase at standard room temperature or pressure. Now remember, in terms of these three phases, in a solid the molecules are very tight packed together. In a liquid they're more free to move around one another, and in gases they're greatly spread apart. So just keep in mind when we're talking about the natural standard state of elements, this is how they exist in terms of phases and in terms of forms. Now, we also have phosphorus, sulfur, and selenium. These don't exist as monoatomic or diatomic atoms. Instead, they're going to exist as polyatomic molecules. Phosphorus exist as p 4, sulfur is s 8, and selenium and tellurium which are below it exist as se8 and te8. Iodine also is diatomic, it exists as I 2. So keep in mind these different forms of the elements in their standard or natural states.
00:46
