Particle Arrangement:
The particles in solids are packed tightly together. In most solids, the particles are arranged in a specific, fixed pattern.

Particle Motion:
The particles are packed so closely together, they cannot move very much. They mainly vibrate in place. Particles cannot move around very much, they have a fixed volume and shape. They do not take the shapes or sizes of their containers.

Particle Arrangement:
The particles in liquids are fairly close together, but not as close together as those in solids. They are not arranged in a fixed pattern.

Particle Motion:
The particles in liquids have enough energy to slide past one another. Particles can move past each other, but are still close together, they have fixed volumes, but not fixed shapes. They take the shapes of their containers.

Particle Arrangement:
The particles in gases are very far apart. They do not have any fixed arrangement.

Particle Motion:
The particles in gases have so much energy that they stay as far apart as possible. They are constantly flying around at very high speeds. Particles are so far apart and move so quickly, they have no fixed volume and no fixed shape. They expand to fill their containers. Gases are also highly compressible—that is, it's possible to reduce their volumes considerably by applying pressure to them. That's because there's so much empty space between the gas particles.

Particle Arrangement:
The particles in plasmas, like those in gases, are very far apart. They do not have any fixed arrangement.

Particle Motion:
The particles in plasmas have even more energy than those in gases. They move even more quickly. Like gases, they are compressible and have neither a fixed volume nor a fixed shape. Plasmas also have another important characteristic: they are made up of highly energetic ions. The particles in plasmas have gained enough energy to lose some of their electrons. Plasmas are actually made up of positively charged particles and negatively charged electrons that move around independently.

matter explains the motions of particles and how matter can transition from one state to another. If you add energy, such as heat, to a substance, the extra energy may cause the particles to move faster. The faster the particles move, the more kinetic energy they have. As you saw in the animation you just explored, when the particles gain enough energy, the substance changes from one state to another.

Similarly, if a substance loses energy, its particles move more slowly. If they lose enough energy, the substance changes to a different state. Complete the activity below to explore the relationship between energy and physical state. Identify whether you would have to add energy or remove energy to cause the state change described in each scenario.

characteristics of a substance that can be measured without changing the identity of the substance. Examples of physical properties:

• Appearance (for example, color or shape)
• Odor
• Melting point and boiling point
• Density
• Hardness
• Ductility and Malleability (ability to change shape)
• Solubility
• Electrical and thermal conductivity
• Magnetism

characteristics of a substance that describe the ways it can react to form new materials. Chemical properties cannot be measured or studied without changing the composition of the substance.

Examples of chemical properties:

• Flammability and other tendencies to react with oxygen
• Reaction with acids and bases
• Reaction with water
• Decomposition caused by light or heat
• Tendency to corrode

states that mass cannot be created or destroyed. Mass is a measure of the amount of matter in a material. This law applies to both chemical and physical changes. To put the law another way, the amount of matter before the change equals the amount of matter after the change. This is logical because the masses of all the atoms are constant, and the number of atoms does not change.

The chemical change in the activity below will demonstrate the reaction of baking soda (sodium hydrogen carbonate) with vinegar (acetic acid) to produce carbon dioxide, water, and sodium acetate. When the balloon is tipped up, the baking soda falls into the vinegar, and the reaction begins.

protons, neutrons and electrons. The nucleus contains only protons and neutrons.

• Protons are particles with a positive charge.
• Neutrons are particles with a neutral, or no, charge.
• Electrons are particles that orbit around the nucleus in regions with different levels of energy. Electrons are much smaller in size and mass than protons and neutrons and have a negative charge.

do not exist as individual particles. Atoms tend to combine with other atoms to form molecules. The atoms in molecules are linked together through chemical bonds.

The tendency for an atom to bond to another atom depends on several things. In this lesson, we will examine how the number of electrons in an atom’s outermost energy level largely determines an atom's ability to form bonds.

contains covalent bonds between the two hydrogen atoms and the oxygen atom. Recall that in a covalent bond the valence electrons are shared by both atoms in the bond.

Some atoms that form covalent bonds share the valence electrons equally. In the case of a water molecule, this is not true.The valence electrons spend more time near the oxygen atom than they do near the hydrogen atoms because of this attraction.

The bonds between oxygen and hydrogen in water are called polar covalent bonds. In a polar covalent bond, the electrons spend more time near one of the atoms than the other.

Polar covalent bonds most commonly form between atoms of elements that are far apart on the periodic table.

All of the positive charge is concentrated on one side of the water molecule, and the negative charge is concentrated at the other. Therefore, the water molecule is said to be a polar molecule. Each water molecule acts like a tiny, electrically charged particle.

The positive "side" of the water molecule can attract negatively charged particles. The negative "side" can attract positively charged particles.

Water has some unusual properties compared to many other substances. Many of these properties are vital to life as we know it. Many of water’s properties are the result of the partial charges on the water molecule and the hydrogen bonds that form between the positive end of one water molecule and the negative end of another water molecule.

When most liquids freeze, the molecules pack together and move closer. Water is an exception. When water molecules freeze, they actually move farther apart.

Look again at the arrangement of the water molecules in liquid water. Notice that the molecules are not bonded together in any special arrangement. Also notice that hydrogen bonds do not form between each positive and negative end of nearby molecules. Now watch what happens when water freezes.

The amount of heat needed to raise the temperature of 1 gram of a substance 1°C.A substance with a high specific heat requires more heat energy to raise its temperature than a substance with a low specific heat. A substance with a low specific heat will heat up and cool down more quickly than a substance with a high specific heat.

Liquid water heats up and cools down slowly. We can say that it resists changes in temperature. This property of water affects the climate in many places around the world. Areas near a large body of water generally do not experience great temperature extremes. The water keeps these coastal regions warmer in winter and cooler in summer than regions farther inland.

A covalent bond in which the electrons are shared equally between the atoms is called a nonpolar covalent bond. Nonpolar covalent bonds typically form between atoms of the same element.

It is important to realize that most bonds are not completely polar or completely nonpolar. Some bonds lie somewhere in between.

Many bases contain hydroxide ions. Their chemical names reflect this. Here are some examples:

• Bitter taste (Never taste or smell a substance unless your parent/guardian tells you that it is okay!)
• Slippery feeling (Never touch a substance unless your parent/guardian tells you that it is okay!)
• Increases the concentration of hydroxide ions when added to water
• Forms salt and water when added to an acid

pH is a measure of the concentration of H⁺ ions in a solution of an acid or base. The pH scale plots the concentration of solutions in a range from 0–14.

Pure water is a neutral substance and has a pH of 7. Substances with pH values below 7 are acids. The closer to 0 a solution is on the scale, the higher the concentration of H⁺ ions in the solution.

Substances with pH values above 7 are bases. The closer to 14 a solution is on the scale, the lower the concentration of H⁺ ions.

You may have noticed that the chemical equations in the previous exercise contain more than just the chemical formulas and the states of matter. They also include numbers before some of the chemical formulas. A coefficient is a whole number placed in front of a formula in a chemical equation.

A coefficient in front of a formula indicates the number of molecules of that substance that take part in the chemical reaction. In the reaction 2H₂(g) + O₂(g) → 2H₂O(l), 2 molecules of hydrogen must combine with 1 molecule of oxygen to produce 2 molecules of water. When no coefficient appears before a formula, assume that 1 molecule (or atom) of that substance is present.

2H₂(g) + O₂(g) → 2H₂O(l)

a substance combines with oxygen and releases energy in the form of heat and light. We use combustion reactions every day to produce energy.

This type of reaction can produce enough energy to send a shuttle into space.