# Matter and measurements
## Introduction

Matter is everything that is made out of atoms. Matter can be defined as anything that has mass and volume. Mass is very similar to a property of matter called inertia (resistance to a change in motion), but for our purposes, it is a measurement of matter (how much matter an object contains). Volume is the amount of space occupied by an object. Weight is the force of gravity on an object, and its formula is $w=mg$ (mass and acceleration of gravity).
Atoms are thus called the building blocks of the universe. An atom is the smallest unit of an element that still maintains the properties of that element. An element is a pure substance made of only one type of atom. For example, the air around you is largely nitrogen gas (with a mix of other gases, such as oxygen). Nitrogen is an atom, and no two nitrogen atoms are distinguishable from one another if they are the same isotope (same number of neutrons). They have identical properties, thus they're the same element. There are approximately 118 different atoms/elements. These elements are available on the The periodic table.
The term "atom" comes from the Greek word for indivisible, because it was once thought that atoms were the smallest things in the universe and could not be divided. We now know that atoms are made up of three particles: protons, neutrons and electrons — which are composed of even smaller particles, such as quarks.

## Matter
### Physical states of Matter

In a solid, the molecules are arranged in designated, stiff patterns due to strong forces between the molecules. Although strongly squeezed together with little room, they can vibrate [in their limited area].
In a liquid, the molecules are more spaced out but are still kept relatively near each other and are able to flow around each other. They are kept from flying around by the attractive forces between them. Liquids take the shape of whatever container they're put in (a glass of water, for example).
In a gas, the molecules freely fly all over the place. What happened to that attractive force? Well, since they are so spaced apart, their attractive force is very insignificant.
In a plasma (high temperatures in a star), the atoms lose their electrons. Plasma is basically electrons + nuclei that results from the atoms losing their elections.

### Intensive vs. Extensive Properties

    see more: https://www.thoughtco.com/intensive-vs-extensive-properties-604133
Intensive Properties are properties that depend upon the type of substance, not the amount of sample--examples are density, boiling point, and freezing point.
Extensive Properties are properties that depend on the amount of sample present--examples are mass, volume, and weight.

### Chemical vs. Physical Properties

    see http://www.mcwdn.org/chemist/pcchange.html
Physical properties/changes are the quality or conditions that can be observed without changing the composition of substance; change where you can get back the original components. Examples are phase changes, b. p., f. p., density, melting point, etc.
Chemical properties/changes are changes that form a new substance and energy is either absorbed or given off. Examples are rusting, burning/combustion, digesting food and baking/cooking.

## Pure Substance vs. Mixture

A pure substance has a well-defined structure and constant composition. They're either an element or compound. An element is composed of one type of atom (such as gold, oxygen, lead--remember Br$_2$I$_2$N$_2$Cl$_2$H$_2$O$_2$F$_2$) while a compound is 2+ chemicals/molecules combined (H$_2$O, NaCl, CO$_2$). An element is only seperable by nuclear reactions--either fission or fusion. Fission is where a heavy nucleus is separated, which happens in nuclear powerplants/atomic bombs. Fusion is where two light nuclei are merged together (which, surpisingly, releases way more energy than fission). An example is in the sun, where two hydrogen nuclei merge together in order to make helium. A compound is only separable into elements by chemical reactions.

## Measures of Matter
### Mass

Mass measures how matter responds to acceleration - the more mass, the more force it takes to make matter accelerate by the same amount.
There are two SI base units of mass:

#### Moles (mol)
### Volume

Volume is the amount of physical 3D space that matter takes up.
The SI base unit of length is metres (m), in one dimension. Area is measured in 2D, so the base unit of area is m$^2$. Volume is measured in 3D, so the base unit of volume is m$^3$.

### Density

Density is a simple function defined as follows:
density = mass / volume
This gives the amount of mass a given volume of matter takes up, and vice versa.