General Chemistry/Properties of Matter/Basic Properties of Matter

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[edit] What is Matter?

Matter, including randomly placed concrete blocks, has mass and volume.

Matter is anything that has mass and volume. Matter is composed of atoms, which are then composed of "elementary particles": protons, neutrons, and electrons.

Mass is a measure of an object's inertia. It is proportional to weight: the more mass an object has, the more weight it has. However, mass is not the same as weight. Weight is a force from gravity, and mass is the the object's resistance to change in motion, its "heaviness". Mass is measured with a scale.

Volume is the amount of space that an object takes up. Volume can be measured in several ways, including a graduated cylinder and length measurements. A graduated cylinder is a tube that holds liquid. It is marked and labeled at regular intervals, usually every 1 or 10 mL. Objects that have regular shape, like a box, can have their volume calculated by measuring its dimensions. In the case of a box, its volume equals length times width times height.

The amount of substance is something like the number of the parts of the object. Those parts are measured with various units, such as the pair, the dozen, and the mole. One pair is two units, one dozen is 12 units, and one mole is 6.022 x 10²³ units. One mole of carbon atoms weighs exactly 12 g and is composed of 6.022 x 10²³ atoms. The type of the substance that is being measured must be specified — for example, a pair of shoes, a dozen eggs, a mole of carbon atoms.

[edit] Atoms, Elements, and Compounds

The fundamental building block of matter is the atom.

The red dots are protons and the blue dots are neutrons.

Any atom is composed of a little nucleus surrounded by a "cloud" of electrons. In the nucleus there are protons and neutrons.

However, the term "atom" just refers to a building block of matter; it doesn't specify the identity of the atom. It could be an atom of carbon, or an atom of hydrogen, or any other kind of atom.

This is where the term "element" comes into play. When an atom is defined by the number of protons contained in its nucleus, chemists refer to it as an element. All elements have a very specific identity that makes them unique from other elements. For example, an atom with 6 protons in its nucleus is known as the element carbon. When speaking of the element fluorine, chemists mean an atom that contains 9 protons in its nucleus.

It is important to note that if the number of protons in the nucleus of an atom changes, so does the identity of that element. If we could remove a proton from nitrogen (7 protons), it is no longer nitrogen. We would, in fact, have to identify the atom as carbon (6 protons). Remember, elements are unique and are always defined by the number of protons in the nucleus. The Periodic Table of the Elements shows all known elements organized by the number of protons they have.

An element is composed of the same type of atom; elemental carbon contains any number of atoms, all having 6 protons in their nuclei. In contrast, compounds are composed of different type of atoms. A carbon compound contains some carbon atoms (with 6 protons each) and some other atoms with different numbers of protons.

It's important to understand that compounds have different properties than the elements that created them. Water, for example, is composed of hydrogen and oxygen. Hydrogen is an explosive gas and oxygen is a gas that fuels fire. Water has completely different properties, being a liquid that is used to extinguish fires.

The smallest unit of a compound is called a molecule. Molecules are composed of atoms that have "bonded" together. As an example, the formula of a water molecule is "H₂O": two hydrogen atoms and one oxygen atom.

[edit] Properties of Matter

Properties of matter can be divided in two ways: extensive/intensive, or physical/chemical.

[edit] States of Matter

One important physical property is the state of matter. Three are common in everyday life: solid, liquid, and gas. The fourth, plasma, is found in the sun and in fluorescent lamps. Substances can exist in any of the states. Water is a compound that can be liquid, solid (ice), or gas (steam).

The ice in this picture is a solid. The water in the picture is a liquid. There is water vapor in the air, and that is a gas.

The states of matter depend on the bonding between molecules.

[edit] Solids

Solids have a definite shape and a definite volume. Most everyday objects are solids: rocks, chairs, ice, and anything with a specific shape and size. The molecules in a solid are close together and connected by intermolecular bonds. Solids can be amorphous, meaning that they have no particular structure, or they can be arranged into crystalline structures or networks. For instance, soot, graphite, and diamond are all made of elemental carbon, and they are all solids. What makes them so different? Soot is amorphous, so the atoms are randomly stuck together. Graphite forms parallel layers that can slip past each other. Diamond, however, forms a crystal structure that makes it very strong.

[edit] Liquids

Liquids have a definite volume, but they do not have a definite shape. Instead, they take the shape of their container (or the shape of a puddle if there is no container). The molecules are close, but not as close as a solid. The intermolecular bonds are weak, so the molecules are free to slip past each other, flowing smoothly. A property of liquids is viscosity, the measure of "thickness" when flowing. Water is not nearly as viscous as molasses, for example.

[edit] Gases

Gases have no definite volume and no definite shape. They expand to fill the size and shape of their container. The oxygen that we breathe and steam from a pot are both examples of gases. The molecules are very far apart in a gas, and there are minimal intermolecular forces. Each atom is free to move in any direction. Gases undergo effusion and diffusion. Effusion occurs when a gas seeps through a small hole, and diffusion occurs when a gas spreads out across a room. If someone leaves a bottle of ammonia on a desk, and there is a hole in it, eventually the entire room will reek of ammonia gas. That is due to the diffusion and effusion. These properties of gas occur because the molecules are not bonded to each other.

Technically, a gas is called a vapor if it does not occur at standard temperature and pressure (STP). STP is 0° C and 1.00 atm of pressure. This is why we refer to water vapor rather than water gas.