CHAPTER 4

SECTION 1

  1. Matter can be classified into elements, compounds, and mixtures.

Elements, the Simplest Substances

  1. An element is defined as a pure substance that cannot be broken down into simpler substances by chemical means.
  1. A pure substance is a substance that contains only one kind of particle.
  1. An element contains only one kind of particle. – The atom!

Properties of Elements

  1. Each element can be identified by its unique properties. These properties are referred to as characteristic properties.
  1. Characteristic properties include physical and chemical properties.

Classifying Elements by Their Properties

  1. Elements are grouped into categories according to the properties they share.

2. There are 3 major categories of elements.

a. metals – shiny, conduct heat and electricity

b. non-metals – dull, non-conductors

c. metalloids – have properties of both metals and non-metals

SECTION 2

  1. Because most elements easily change chemically, they are rarely found alone in nature.

Compounds: Made of Elements

  1. A compound is a pure substance that is made of 2 or more elements that have combined chemically.
  1. A particle of an element is an atom. A particle of a compound is a molecule.
  1. When elements join to form a compound, they do so in a specific ratiobased on their masses

Properties of Compounds

  1. Compounds have physical and chemical properties.
  1. A compound’s properties are different than the properties of the elements that came together to make the compound.

Breaking Down Compounds

  1. Some compounds can be broken down by chemical changes into the elements that make them.
  1. Some compounds do not break down into their elements, but into other simpler compounds.
  1. Chemical changes are required to break down compounds.
  1. The addition of energy may be necessary to cause the chemical change. Energy can be added by applying heat or an electric charge.

SECTION 3

  1. A mixture also contains elements.

Properties of Mixtures

  1. A mixture is defined as a combination of 2 or more substances that are not chemically combined.
  1. No chemical change happens when a mixture forms. Each substance in a mixture keeps its identity.
  1. With a mixture, you may or may not be able to see the substances making it.
  1. Mixtures can be separated by physical means such as boiling or filtering.
  1. Distillation is a process that separates a mixture based on the boiling points of the components. E.g. Crude oil into gasoline and kerosene
  1. Magnetism can separate mixtures of the elements iron and aluminum.
  1. Centrifuge separates mixtures by the densities of the components. E.g. separating plasma from the layer of red blood cells.
  1. The components of a mixture are not necessarily in a specific ratio like a compound.

Solutions

  1. A solution is a mixture that appears to be made of just one substance, but in fact is composed of different substances.
  1. The substances making up a solution are evenly distributed among one another.
  1. The process by which substances evenly disperse is known as dissolving.
  1. The solute is the substance that is dissolved, or dispersed between the particles of the solvent.
  1. The solvent is the substance in which the solute dissolves.
  1. A solute must be soluble to dissolve. If a substance is insoluble, it forms a mixture, not a solution.
  1. Solutions may be liquids, gases, or solids.
  1. With a solution, the particles of the solute are so small they never settle out of solution, nor do they scatter light.

Concentrations of Solutions

  1. Concentration is a measure of the amount of solute dissolved in a solvent.
  1. Solutions will either be concentrated or dilute.
  1. If a solution is concentrated, there is a lot of solute in the solvent.
  1. If the solution is dilute, there is not a lot of solute in the solvent.
  1. The solubility of a solute is the ability of the solute to dissolve in a solvent at a certain temperature.
  1. Most solutes dissolve more readily at higher temperatures.
  1. Heating, mixing and crushing the solute will also increase rates of dissolving.

Suspensions

  1. A suspension is defined as a mixture in which particles of a material are more or less evenly dispersed throughout a liquid or gas.
  1. The particles in a suspension are large enough that they settle out and scatter light.
  1. The particles are so large that the suspension must be shaken or stirred to stay mixed.
  1. A suspension can be easily separated into the substances that make it up by filtering.

Colloids

  1. A colloid is defined as a mixture in which the particles are very fine and dispersed pretty evenly among each other.
  1. The particles in a colloid are so small that they do not settle out.
  1. The particles in a colloid will scatter light.
  1. Filtration will not separate the particles of a colloid because the particles are too small to be caught by the filter.

Heterogeneous vs. Homogenous Mixtures

  1. Mixtures can be categorized by their particle size and distribution.

HOMOGENEOUS MIXTURES / HETEROGENEOUS MIXTURES
The prefixes "homo"- indicate sameness / The prefixes:"hetero"- indicate difference.
A homogeneous mixture has the same uniform appearance and composition throughout. Many homogeneous mixtures are commonly referred to as solutions. / A heterogeneous mixture consists of visibly different substances or phases (solids, liquids, gases).
Particle size distinguishes homogeneous solutions from other mixtures. Solutions have particles which are the size of atoms or molecules - too small to be seen.
A colloid is a homogeneous solution with intermediate particle size between a solution and a suspension. Colloid particles may be seen in a beam of light such as dust in air in a shaft of sunlight. Milk, fog, and jello are examples of colloids.
/ A suspension is a heterogeneous mixture of larger particles. These particles are visible and will settle out on standing. Examples of suspensions are: fine sand or
silt in water or tomato juice.
Corn oil is homogeneous, White vinegar is homogeneous. A sugar solution is homogeneous since only a colorless liquid is observed. Air with no clouds is homogeneous. / Beach sand is heterogeneous since you can see different colored particles. Vinegar and oil (Italian salad dressing) salad dressing is heterogeneous since two liquid layers are present, as well as some solids. Air with clouds is heterogeneous, as the clouds contain tiny droplets of liquid water