The MIDAS Project: Supported by the Science Education Partnership Award Program of the National Center for Research Resources, National Institutes of Health (Grant No. R25 RR018634)

Matter and Chemicals TEKS: 8.9B, 8.9C, 8.10C

Phases of Matter (also known as the States of Matter)

Solids have a definite shape and volume, the atoms are tightly packed and bound so that only vibrations occur. The molecules do not move around within the substance.

Liquids have a definite volume but they do not have a definite shape. Liquid particles move freely. Liquids take on the shape of their containers.

Gases have no definite shape or volume. The atoms are in constant motion and collision. The atoms are much further apart. Gas particles fill all the available space in a container.

Plasmas have no definite shape or volume, just like gases, but they are different. In a plasma, the molecules are in a very high state of vibration.

Plasma is very rare on earth. In nature it is seen as lightning. Stars are gases in the plasma state.

Facts to Remember! Phase changes are caused by adding or taking away energy. (heat)

Melting – is the change from a solid to a liquid and occurs when a substance absorbs heat (heat is added). Example: when ice changes to water

Freezing – is the change from a liquid to a solid and occurs when a substance loses heat (heat is taken away). Example: when water changes to ice

Evaporation (or boiling point) – is when a substance changes from a liquid to a gas. Example: when water boils into steam

Condensation – is when a substance changes from a gas to a liquid Example: when water forms on the mirror in your bathroom when you take a shower

Sublimation – is when a substance changes from a solid to a gas Example: when ice changes directly into a gas and forms a fog coming out of your freezer when you open the door.

As things get warmer their molecules move faster. As molecules move faster they bump into one another and the object gets bigger or expands.

As things get colder, they move slower and get closer together. The object gets smaller or contracts.

EXCEPTION: Water is the only substance that gets bigger when it freezes!

Changes in Matter

Physical Change A physical change is when a substance changes from one form to another, but it remains the same substance.

It may change phases (from solid to liquid to gas) or it may break into pieces but its still the same stuff. When water freezes, it turns into ice, but it is still water.

When matter changes phase it is considered a physical change.

Chemical Change A chemical reaction is a change in matter that produces one or more new substances. This is different from a physical change in matter where something changes shape, size, phase or temperature.

In a physical change the matter is still the same substance. Like a window pane breaking, the glass is still glass; it’s just broken glass.

In a chemical reaction, the substance changes into a completely new substance. When wood burns, it changes to ash and gases. This is a chemical change.

Sometimes it is not easy to tell the difference between a chemical and a physical change. Here are 5 types of evidence to check to see what kind of a change has occurred.

1.Changes in Properties When a substance changes into a new substance with different properties it is called a chemical change. For example, bread is very different from bread dough.

When yeast, flour, salt, and water are mixed and heated, they become a flaky, crusty, loaf of bread with very different properties from the bread dough.

2.Temperature Changes When two or more substances are mixed and cause a temperature change a chemical change has taken place.

This is a change in energy. Some chemical reactions absorb energy and some release energy.

When a chemical reaction absorbs energy the substance gets colder.This is called an endothermic reaction.

When a chemical reaction releases energy the substance gets warmer and it is called an exothermic reaction.

3. Gas Production When two chemicals are mixed and a gas is formed then a chemical reaction has taken place. An example of this is when baking soda and vinegar are mixed, carbon dioxide bubbles form.

4. Color Change When chemicals change color they may have gone through a chemical change. Bleaching clothes is a chemical change and so are the changing color of leaves in the fall.

5. Precipitation When two solutions are mixed and a solid is formed it is called a precipitate. This is also evidence that a chemical change has taken place.

Types of Chemicals

Elements An atom is the smallest particle that an element can be and still be that element. One atom of gold may be so tiny that you cannot see it, but it is still gold and has all the properties of gold.

Electron Microscope photograph of a gold atom.

If it is broken down into smaller pieces it is no longer gold, it is protons, electrons and neutrons.

Compounds If two or more elements combine chemically and make a new substance, they become a compound. A good example is water.

Calcium is not found in nature as an element. It is always bonded to other elements as a compound. Calcium Carbonate or calcite is the most common calcium compound found in nature.

If 2 atoms of hydrogen chemically bond to 1 atom of oxygen a molecule of water is formed. A molecule is the smallest particle that a compound can be and still be that compound.

One molecule of water has all the properties of a glass of water, but if it is broken down into smaller pieces, they are atoms of oxygen and hydrogen, not water.

Chemical Bonds A chemical bond is a force that holds atoms together in compounds. The electrons in the atoms are the important particle in a bond. When chemical bonds form, electrons are either transferred or shared between atoms.

There are 2 types of chemical bonds. When atoms share electrons the bond is called a covalent bond. When electrons are transferred the bond is called an ionic bond.

Mixtures If 2 or more substances are mixed together but do not chemically combine the substance is called a mixture. Substances in a mixture keep their separate identities and most of their own properties.

They may change physical properties, but not their chemical composition. Mixtures can be separated back into their original substances.

Gold jewelry is usually not pure. It is an alloy. An alloy is a mixture of metals. Gold is commonly mixed with copper or zinc to make it stronger.

A good example of this is sugar water. The sugar seems to disappear in the water, but it still tastes like sugar and if you evaporate the water away you will have sugar again.

Solutions Sugar water is an example of a type of mixture called a solution. A solution is formed when one substance dissolves into another.

An amalgam is any alloy of mercury. Most metals are soluble in mercury, but some (such as iron) are not. Amalgams are commonly used in gold mining and can have terrible effects on the environment because they are very toxic to many animals.

There are parts to a solution. The solute is the substance that is being dissolved and the solvent is the substance that does the dissolving. Example: Solution – lemonade Solute – Lemon juice and sugar Solvent - water

A solid is said to be soluble if it can be dissolved in water. Water is considered to be the universal solvent because many, many substances will dissolve in water.

A substance is said to be insoluble if it cannot be dissolved in water.

A solution is a mixture and not considered to be a compound because the elements are not chemically bonded.