Phases of Matter, Atoms, Elements, Molecules, Mixtures

What is matter?

Matter is anything that has mass and takes up space. Everything around us is made of matter, including the air that we can’t see. It can exist in three main forms: solid, liquid, and gas. Here is a graphic that summarizes the characteristics of each phase of matter:

When you heat matter, it will go from a solid to a liquid, and then to a gas. Similarly, cooling matter will convert it in the opposite direction (gas to liquid to solid). The properties of the different phases are brought about by the movement of tiny particles that make up matter, called atoms (see below). The higher the temperature, the more excited and rapid the atoms' movements become.

What are atoms and elements?

Atoms are the basic unit of matter and are essentially the smallest things in the world (though they are composed of smaller parts!). As such, all matter is composed of atoms, organized into various structures through chemical bonds.

An atom itself is made up of three tiny kinds of particles called subatomic particles: protons, neutrons, and electrons. The protons and the neutrons make up the center of the atom called the nucleus and the electrons orbit the nucleus in a small “electron cloud,” zipping around at really high speeds.

Electrons, which are negatively charged, orbit the nucleus because they are attracted to the positive charge of its protons. Although neutrons have no charge, they contribute to the mass of the atom, which can affect a lot of chemical interactions that atoms participate in.

Elements are different types of atoms, classified by the number of protons they have. Since all matter is made of atoms, it makes sense that all matter is also composed of different elements. For example, oxygen is an element with 8 protons, and around 21% of the air we breathe is made of oxygen.

If you were to hypothetically add or take away protons from an atom, it would become a different element. Elements are typically abbreviated to single- or double-letter symbols. For example, oxygen is abbreviated to O, and sodium (an element found in table salt) is abbreviated to Na. The periodic table organizes elements by increasing atomic number (among other things), or the number of protons it has.

What happens when you combine atoms/elements?

Atoms can chemically join together to form substances with different chemical properties. When two or more atoms join and form these chemical bonds, they become a molecule. A compound is a type of molecule that is made up of different elements; all compounds are molecules, but not all molecules are compounds. For example, oxygen normally exists as two oxygen atoms paired together in an oxygen molecule (notated as O2), but it is not a compound because O2 is only made of one type of element.

What are mixtures and solutions?

A mixture is when two or more substances are combined without chemically interacting (without forming compounds). Think of mixing sugar and salt together. Even though they are in the same bowl, they do not form a new substance as a mixture, and you can still physically separate them without using chemical processes. Picking up a single grain from the bowl, you will get either a sugar or a salt grain, but nothing different from the two starting components of the mixture. That is, no new compounds will form.

There are two types of mixtures: heterogeneous and homogeneous mixtures.

A heterogeneous mixture is a mixture whose parts are not evenly distributed. For example, a salad is a heterogeneous mixture because it is made up of different amounts and sizes of vegetables.

A homogeneous mixture is a mixture whose parts are evenly distributed. The air we breathe is a homogeneous mixture of several types of elements and molecules, including nitrogen, oxygen, and carbon dioxide

A solution is a type of homogeneous mixture where one substance (called the solute) is dissolved in another substance (called the solvent).

Saltwater is a good example of a solution. Be careful though: just because you can’t see the salt after it dissolves, this does not mean it chemically transforms into another substance with the water. It is still technically a mixture and NOT a compound because the salt and the water do not chemically combine at the atomic level. This can be proven by the fact that you can still separate the two substances by physical means: if you heat up saltwater, the water will evaporate and leave salt behind!