Directions: Read through this information and then complete the Elements, Compounds, and Mixtures worksheet. Turn into the box when you are finished.

What is matter?Matter is the stuff that makes up everything in the universe. Matter has mass and takes up space. Matter is made of atoms. Solids, liquids, gases, and plasma are all matter. When all atoms that make up a substance are the same, then that substance is an element. Elements are made of only one kind of atom. Because of this, elements are called "pure" substances. An atom is the smallest piece of an element that still has the properties of that element. For example, aluminum is a lightweight, shiny metal. If we took a piece of aluminum and cut it into small pieces, it would still be aluminum. It would still be a lightweight, shiny metal. The smallest piece would be called an atom. Atoms are so small they cannot be seen even with a microscope. Atoms consist of a nucleus that has protons and neutrons surrounded by electrons outside the nucleus. Atoms of different elements can combine to make new substances. A molecule is formed when two or more atoms join together chemically. If atoms combine that are of two or more different elements, we call that a compound. All compounds are molecules, but not all molecules are compounds. When two hydrogen atoms combine with one oxygen atom, it becomes the compound water. The oxygen we breathe is actually two atoms of oxygen combined, so it is a molecule of oxygen. We use abbreviations for elements, molecules, and compounds. These abbreviations are called chemical symbols. The chemical symbol for an oxygen molecule is O2. The compound water has a chemical symbol of H2O. This is like the "recipe" for water. It tells us that a water molecule is made of two atoms of hydrogen and one atom of oxygen. Oxygen is a gas that we can't see, hear, smell, taste, or feel. But it's in the air we breathe, and without it we would die. Hydrogen, also a gas, is the lightest substance on Earth. When two atoms of hydrogen join together with one atom of oxygen, those two gases make a liquid compound we call water. Water, a liquid at room temperature, is a very different substance from the two gases that it is made of. Many different compounds can be made when different atoms combine. There are 93 elements that naturally occur on Earth. Many more have been made by scientists in a laboratory. With that many elements to form combinations, many millions of different molecules and compounds can be made. How is that possible? Think of our alphabet. The English alphabet has 26 letters. Those 26 letters can be combined in different ways to make millions of words. Atoms are like the letters of the alphabet and the compounds they make are like words. Now that you have learned the language of chemistry, you are ready to learn more about elements, atoms, and the ways they combine.

Elements, Atoms, Molecules and Compounds

An element is a basic building block of matter. There are more than 100 elements on the periodic table of elements. Oxygen is only made of oxygen. Elements combine to make all other matter. An element is made up of entirely one type of atom. For example, oxygen is made from oxygen atoms that contain 8 protons. If you change the number of protons an atom has, you change the type of element it is.

An atom is the smallest piece of an element that still has the properties of that element. The atomic number is the most important property of an element because it tells us number of protons. Atoms are composed of particles called protons, neutrons and electrons. The protons and neutrons cluster together in a central part called the nucleus and the electrons orbit the nucleus.

A molecule is formed when two or more atoms are joined together chemically. Oxygen in the atmosphere is a molecule because it is made from two atoms of oxygen. An oxygen molecule is called O2. It is a molecule because it is composed of one type of element.

A compound is what you get when two atoms of two or more different elements join together. Water is a molecule because it is made from atoms that have been chemically combined. It is also a compound because the atoms that make the water are not the same – some are oxygen and some are hydrogen. All compounds are molecules but not all molecules are compounds.

Most things in the world are compounds. When atoms make a compound, the compound’s properties are different from the properties of the atoms. Sugar is make from carbon atoms, hydrogen atoms, and oxygen atoms. But carbon atoms are not sweet. Hydrogen and oxygen are not sweet. Sugar is sweet because carbon hydrogen and oxygen atoms combine in a special way. Every compound has a chemical formula. The formula tells you how many atoms of each element are in the compound. Water has a formula of H20. The H stands for hydrogen. The 2 stands tells you that a molecule of water has two atoms of hydrogen. The O stands for oxygen. There is no number after the O, so there is one atom of oxygen. Every molecule of water has one atom of oxygen and two atoms of hydrogen.

Molecules

Molecules form when atoms are chemically joined together, and are made up of two or more atoms. The size of a molecule depends upon the size and number of atoms that make it up. For example, the oxygen molecules we breathe are made out of only two atoms joined together and can be represented by the chemical formula O2. On the other hand, one molecule of aspirin is made of twenty-one atoms and is represented by the chemical formula of C9H8O4.

Elements

Molecules are classified into two major types: elements and compounds. Remember, if a molecule is made out of only one type of atom, it is an element. Elements can have just one atom, or they can have many of the same atoms joined together. If all of the atoms in a molecule are alike, then the molecule is classified as an element. For example, the O2 we breathe is an element, since both of the atoms are oxygen. Air also contains other elements, such as Helium (H), Nitrogen (N2), Hydrogen (H2), Argon (Ar) and Neon (N).

Which of these elements are molecules and which are atoms?

Compounds

Molecules that have more than one type of atom are called compounds. All molecules are made of atoms that have been joined together. However, if all of the atoms are not the same, the molecule is classified as a compound. The aspirin molecule of C9H8O4 is made of three different types of atoms: carbon atoms, hydrogen atoms, and oxygen atoms. Therefore, C9H8O4 is a compound. Air contains compounds such as carbon dioxide (CO2), methane (CH4), and water vapor (H2O). Notice that all these examples have two or more different elements in them.

Mixtures

Mixtures are composed of two or more substances which each keep their original properties and do not combine chemically when put together. A salad is an example of a mixture. Each part keeps its own properties—lettuce, tomatoes, carrots, peppers all taste like themselves--but they are all combined. The special trait of mixtures is that physical forces can still remove the basic parts. Air is considered a mixture, because it contains different elements and compounds, but each one still maintains its own properties. The oxygen in air is mixed with other elements and compounds, but it is still oxygen.

MIXTURES

Combination of two or more substances that are not chemically combined

  • No new substance formed
  • Do not exist in fixed proportions to each other
  • They just mix
  • Most natural substances are mixtures
  • Can be physically separated into pure compounds or elements
  • Can be separated by mechanical means
  • Physical properties can change
  • Any combination of solid, liquid or gas can be a simple mixture

MIXTURES MAY BE HOMOGENEOUS OR HETEROGENEOUS

Homogeneous Mixtures:

  • The prefix:"homo"- indicates the same
  • Have the same uniform appearance and composition throughout

SOLUTIONS are homogeneous mixtures:

  • A solution is a mixture of two or more substances in a single phase
  • At least two substances must be mixed in order to have a solution
  • The substance in the smallest amount and the one that DISSOLVES is called the SOLUTE
  • The substance in the larger amount is called the SOLVENT - it does the dissolving
  • IN most common instances water is the solvent
  • The gases, liquids, or solids dissolved in water are the solutes

COLLOIDS are another type of homogeneous solutions with a bigger particle size

  • 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

Heterogeneous Mixtures:

  • The prefix:"hetero"- indicates difference
  • A heterogeneous mixture consists of visibly different substances or phases
  • The three phases or states of matter are gas, liquid, and solid
  • A SUSPENSION is a heterogeneous mixture of large particles
  • These particles are visible and will settle out on standing
  • Examples of suspensions are: fine sand or silt in water or Italian salad dressing

PURE COMPOUNDS

A pure compound has the same elements and the same amount of elements all of the time

  • Elements are chemically combined
  • Compound properties are different from the properties of the elements
  • They cannot be separated physically

Physical properties such as boiling point or melting point of pure substances are do not change