General Chemistry Section 1.2: Classifications of Matter

Hello internet, and welcome to the General Chemistry Lecture Series from The Science of Life.  This session will cover the basic classifications of matter from a chemical stand-point.  After all, the only way to identify a substance is through the classifications of matter, whether the classification is obvious is obvious or not.  After all, the difference in the water in Flint, Michigan before and after the switch of water sources as well as between Flint water and Detroit water after the switch was obvious, and that obviousness came from the differences in the classifications of the matter coming out of the faucets.

Obvious differences in classifications are obvious.

There are two principle classification types; physical (phase, temperature, density, for example) and chemical composition (what atoms are present in what arrangement).  I'm going to start off with the physical classifications.

Phase (State)

The phase of something is merely whether it is a solid, a liquid, a gas, or a plasma.  Since chemists really don't work with plasma, I won't much cover it here, but I will cover the other three.

Gases

A gas (or vapor) is a state where there is no fixed volume and no fixed shape.  Any gas conforms in both shape and volume to its container.  Since it's volume conforms to its container, it can be readily compressed or expanded at will.  (This concept will be covered with the ideal gas law of this course as well as the real gas laws of Physical Chemistry 1 and 3.)  The lack of fixed shape means that the gas can flow freely.  This lack of both shape and volume stems from the fact that the molecules of gas are energetic enough to break away from all of the attractive forces of all of the other molecules of the gas so that they are all freely moving independent from the other molecules.

Liquids

A liquid is a state where there is a fixed volume but there is no fixed shape, which means that liquids conform in shape to it's container.  The fixed volume part means that liquids tend to be relatively in-compressible.  Since there is no fixed shape, liquids also tend to flow.  The fact that the volume is fixed also means that the molecules are close enough for intermolecular forces (forces which occur between molecules) to be present.  The fact that the shape is not fixed means that these forces are not strong enough to lock in the relative positions of molecules.

Solids

A solid is a state where both volume and shape are fixed.  In gases and liquids, they conform to their containers; solids are the container.  Since it has fixed volume, it cannot be compressed.  Since it has a fixed shape, there is no tendency of flow.  This comes from the fact that the molecules are rigidly bound together by intermolecular forces.  These forces are far stronger than they are in liquids.  The molecules are also much less energetic (and therefor far slower) than they are in liquids.

Elements and their Symbols

An element is a submicroscopic piece of matter which cannot be chemically decomposed.  When we write out the chemical formula of a substance, we use the element Symbols of all atoms involved.  If you've ever looked at a periodic table, you've seen these symbols.  You've also wondered why some elements have symbols which make sense (Hydrogen - H) while others don't make a lick of sense (Leab - Pb; seems legit).  There is a logic to this, and the logic is as follows: the elements which were known and recognized as their own, distinct elements before we as a species started doing chemistry are given symbols based upon their ancient Latin names.  There is a small list of elements known to pre-chemistry humans.  These elements are lead, copper, gold, silver, mercury, and tin.  There are other elements which were extracted before modern chemistry, but these were not recognized as their own distinct materials, since they seemed to share properties with other known materials.

Combinations of Elements

When an element is alone, it is simply an elemental substance.  Elements can be represented by atoms, and whenever there's only two atoms, then it is a diatomic molecule.  If there is more than two atoms, than it is simply a molecule.  The molecules do not necessarily have the same properties as their component elements.  For example, hydrogen and oxygen are gases at room temperature and atmospheric pressure, but when they combine to form either water or hydrogen peroxide, suddenly we have a liquid at room temperature and atmospheric pressure.

Covalent vs. Ionic Molecules

There are molecules of two different types; covalent and ionic.  If there is at least one bond in the molecule which can be represented as a negatively charged atom being attracted to a positively charged atom, then it is an ionic molecule.  If there is no such bond, then it is classed as a covalent molecule.

Purity

All materials have different levels of purity.  There are different types of purity.  In order to delve into this category, we must first define a chemical (or substance).  A chemical is anything which, in it's pure form, contains at least one (one or more) atom.  The word "chemical" and the word "substance" are often used interchangeably.

Oh the humanity!

Pure Substances

Like it says on the tin, pure substances are those substances which are of purity of the maximum level.  There is literally no impurities in a pure substances.  I doubt this has ever been thoroughly done before, but it is hypothetically possible to have this level of purity.  It has been known for quite a many centuries that the elemental composition and chemical properties of the same pure chemical is the always the same, regardless of whether it was synthesized by humans, aliens, or nature; where it was synthesized; when it was synthesized; or how it was synthesized.

Mixtures

A mixture is two or more chemicals mixed together in the same vessel.  We can have a mixture in gases (the air we breathe), liquids (list any non-water drink here), or solids (list any food we eat or any medication prescribed to us).  We can also mix something of one phase into another.  An example is saline used in hospitals, which is salt (a solid) dissolved into water (a liquid).  Another example is the ocean (a liquid) taking up carbon dioxide (a gas), the main cause of ocean acidification. Most forms of matter we come across in reality come in the form of mixtures.

When one substance is mixed in with another substance, like mixing salt in with water, you can mix any amount of the first into the second.  This means that the average composition of a mixture can be anything you choose to be.  There are some mixtures which can not uniformly mixed, such as a mixture of oil and water.  These mixtures are called heterogeneous mixtures (hetero meaning different).  There are other mixtures which very readily uniformly mix, such as water and sugar.  These mixtures are called homogeneous mixtures (mono meaning "the same").  Even though they are mixed together, each of the components of the mixture retains its own physical properties, such as boiling point and melting point.  This will come in handy next lecture when we cover separation.

That's the end of this section.  If you have any questions, please leave them is the comments.  Like and share this post if you found it helpful, and until next time, stay curious.

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