Chapter 2 The Nature of Matter

Properties of Matter Matter is anything that has mass and takes up space. Chemistry is the study of the properties of matter and how matter changes. In Chemistry, a substance is a single kind of matter that is pure; meaning it always has a specific makeup or composition and a specific set of properties.

Properties of Matter Continued Every form of matter has two kinds of properties – physical and chemical. Pure substances – table salt, table sugar, baking soda. Not substances – flour, baking powder, milk, eggs, and fruit.

Physical Properties of Matter A physical property is a characteristic of a pure substance that can be observed without changing it into another substance. Density, hardness, texture, and color are some physical properties of matter.

Chemical Properties of Matter A chemical property is a characteristic of a pure substance that describes its ability to change into different substances. Chemical properties would be forming new substances with new properties, the ability to react, and flammability.

Elements An element is a pure substance that cannot be broken down into any other substances by chemical or physical means. Elements are the simplest substances and can be identified by its specific physical and chemical properties. An atom is the basic particle from which all elements are made.

Elements Continued When atoms combine, they form a chemical bond, which is a force of attraction between two atoms. In many cases, atoms combine to form larger particles called molecules, which are groups of two or more atoms held together by chemical bonds.

Compounds A compound is a pure substance made of two or more elements chemically combined in a set ratio. A compound may be represented by a chemical formula, which shows the elements in the compound and the ratio of atoms. When elements are chemically combined, they form compounds having properties that are different from those of the uncombined elements.

Ratios A ratio compares two numbers. It tells you how much you have of one item compared to how much you have of another. For example, a cookie recipe calls for 2 cups of flour to every 1 cup of sugar. You can write the ratio of flour to sugar as 2 to 1, or 2:1.

Ratio Example The chemical formula for rust, a compound made from the elements iron (Fe) and oxygen (O), may be written as Fe 2 O 3. In this compound, the ratio of iron atoms is 2:3. This compound is different from FeO, a compound in which the ratio of iron atoms to oxygen atoms is 1:1.

Practice Problem What is the ratio of nitrogen atoms (N) to oxygen atoms (O) in a compound with the formula N 2 O 5 ? Is it the same as the compound NO 2 ? Explain

Solution N 2 O 5 contains 2 nitrogen atoms for every 5 oxygen atoms. The ratio is written as 2:5. The two compounds are different because NO 2 contains one nitrogen for every two oxygen atoms.

Mixtures A mixture is made of two or more substances, such as: elements, compounds, or both that are together in the same place but are not chemically combined. Each substance in a mixture keeps its individual properties. Also, the parts of a mixture are not combined in a set ratio.

Mixtures Continued Heterogeneous mixtures allow you to see the different parts. Homogeneous mixtures are so evenly mixed that you can’t see the different parts. A solution is an example of a homogeneous mixture. Several methods exist to separate mixtures. They include magnetic attraction, filtration, distillation, decantation, and evaporation.

Changes in Matter A physical change is any change that alters the form or appearance of matter but does not make any substance in the matter into a different substance. A substance that undergoes a physical change is still the same substance after the change. A change in the state, shape, color or size are all physical changes.

Changes in Matter Continued A change in matter that produces one or more new substances is a chemical change, or a chemical reaction. Unlike a physical change, a chemical change produces new substances with properties different from those of the original substances. Examples of chemical changes would be combustion, electrolysis, oxidation, and tarnishing.

Conservation of Matter The fact that matter is not created or destroyed in any chemical or physical change is called the law of conservation of matter. Mass always measures the amount of matter.

Energy and Matter Energy is the ability to do work or cause change. Forms of energy related to changes in matter include thermal energy, chemical energy, electromagnetic energy, and electrical energy. Temperature is a measure of the average energy of random motion of particles of matter.

Energy and Matter Continued Thermal energy is the total energy of all the particles in an object. Thermal energy always flows from warmer matter to cooler matter. 2 types of thermal energy: endothermic and exothermic. The melting of ice is an endothermic change in which energy is taken in or absorbed. Exothermic change releases energy or energy is given off such as in combustion.

Forms of Energy The energy stored in the chemical bonds between atoms is a form of energy called chemical energy. When a chemical change occurs, chemical bonds are broken and new bonds are formed. Visible light is one example of electromagnetic energy, a form of energy that travels through space as waves. Chemical changes can give off electromagnetic energy such as light from a wood fire. Electrical energy is the energy of electrically charged particles moving from one place to another.

Electrolysis Process 2 Metal strips called electrodes are placed in a solution. Each electrode is attached to a wire. Wires are connected to a battery. Electric current flows and atoms of one kind lose electrons at one electrode in the solution. At the other electrode, atoms of a different kind gain electrons. New substances form at both electrodes as a result.

Transforming Energy During a chemical change, chemical energy may be changed to other forms of energy. Other forms of energy may also be changed to chemical energy.