in chemistry. Everything that we study consists of matter. Matter is something that occupies space and has a mess. Mass is defined as the amount of matter that it contains, and it is often measured in things like grams or kilograms. It is important to note that mass is not measured in pounds, which is a weight that is dependent on the gravitational pole of another mass. In nature. There are technically for states of matter, but in this course we will be focusing on three, which is the guest liquid and solid phases. So for the gas phase, these are made up of atoms or molecules that are not bound together, which move independently of each other in all directions in three dimensional space and are also shapeless, meaning that they will spread out to fill any container or space that they can occupy. Gasses are also compressible if they're subjected to changes in pressure or temperatures, so if you increase the pressure, you will compress the gas, and if you decrease the pressure, the gas will expand and these changes will also occur with changes in temperature and examples of gasses include things like oxygen, gas, hydrogen gas as well as carbon dioxide. So the next phase that we will be talking about is the liquid face. And for liquids, thes atoms or molecules can move freely around each other, but to is to a certain extent because they are loosely bound together. There are also amorphous, and we'll take the shape of the container that it is in. And they're not compressible under changes, impression or temperature and therefore have a fixed volume. And examples of thes include something like water that we're all very familiar with, as well as elemental mercury, which at room temperature is a liquid and it is often found in traditional thermometers. So the last phase that we will be talking about is the solid phase. And in the solid phase, atoms or molecules are bound together, resulting in a rigid structure. They don't move around each other, bubble, move in place or vibrate in place. And like liquids, they're not compressible on our changes in pressure and temperature, and therefore have a fixed volume as well. And examples of these include sodium chloride or more well known as table salt for the mineral highlight, and another example would be solid water which we call ice. So matter can exist and these three different states and can also undergo something called a phase change. Where matter changes from one state to another state via the making or breaking of inter molecular bonds, which are bonds between molecules and an example of this would be liquid water freezing into ice in the freezer section of a bridge. So in addition to face changes, matter can also physical and chemical properties. Physical properties can be further broken down into something called extensive and intensive properties. So first off examples of physical properties include things like math melting. Point minus is, um, etcetera, and these can be further categorized into extensive and intensive properties, so expensive properties are dependent on the amount of stuff the substance has. So things like mass and volume are expensive properties, because if you have more matter by virtue, you have more mass and more volume. Everything else on this list are intensive properties, which are independent of the amount of Seth the substance has. So regardless of whether you have something like 1 g of sugar or 30 g of sugar, all of these will melt and boil at the same point. And in addition to physical properties, matter also has chemical properties, and examples of these include flammability and reactivity and reactivity is how matter can interact with other types of matter through intra molecular bonding or bonding between Adams.