Structure and Change Chapter One

Chemistry is the study of the composition, structure, and properties of matter, the processes that matter undergoes, and the energy changes that accompany these processes.

Most often, chemists become interested in microstructures.

A chemical is any substance that has a definite chemical composition.

Basic research is done for the sake of increasing knowledge. (basic chemist)

Applied research (research chemists) work to solve everyday problems.

Technological development (chemical engineers) studies the production and use of products that improve our daily lives.

Matter and It’s Properties

Each object around you is matter. Matter is everything that is anything. Matter is defined as anything that has volume (takes up space) and mass. Mass is the measure of the amount of matter in an object.

The Building Blocks of Matter An element is the simplest form of matter that retains the properties of that element. An atom is the smallest part of an element. A compound is a substance that is made up of two or more elements that are chemically combined. For now, you can consider a molecule to be the smallest part of a compound.

Properties and Changes in Matter Characteristic properties are traits that can be used to distinguish and separate matter. Extensive properties depend on the amount of matter present. Intensive properties donot depend on the amount of matter present. A physical property is a trait that can be observed without changing the identity of the substance. These might include melting, evaporating, crushing, bending, mixing, and dissolving. One should remember that since a physical change only affects physical properties, it can be undone. A chemical property is a trait that is shown as a substance changes its identity. These would include baking a cake, the souring of milk, the burning of fuel, rusting, and the fizzing away of an alkaseltzer.

A physical change is a change that does not involve a change in the identity of matter. The most basic physical change is the change of physical state.

The Four States of Matter The states of matter at the four physical forms that a substance can exist in. These are a gas, a liquid, a solid, or a plasma. In a solid, the particles are not moving but are only vibrating in place. The attractive forces hold the particles in rigid position giving a solid a definite volume and a definite shape. In a liquid, the particles are moving fast enough to slide past each other but they stay attached together. This lets a liquid take the shape of its container but it still will have a definite volume.

In a gas, the particles are moving so fast that they escape all forces of attraction. This causes a gas to have no definite shape and no definite volume. Regardless of the shape or volume of the container, gases will fill them.

Chemical properties are those properties that are based on the ability of a substance to change into a different substance. These might include flammability, reactivity to acids and bases, reactivity with water, and oxidation As one studies the change of reactents to products in chemical reactions, it should always be remembered that energy is involved.

There is a definite set of clues that a chemical change is taking place: temperature change evolution of a gas formation of a precipitate (new solid) production of light production of electric current production of sound color change

As a chemist evaluates the characteristics of a reaction, it is important to remember that energy transfer always accompanies a chemical reaction.

Classification of Matter

Matter exists in a wide variety of forms, however, the basic classification of matter is almost always as a pure substance or a mixture.

Mixtures are a blend of two or more substances that : Are considered heterogeneous or homogeneous May be physically separated May exist in a variety of concentrations

If a mixture contains large particles dispersed in a liquid or a gas that will settle out, it is classified as a suspension. If the particles of a suspension are not stirred constantly, they will settle out as in a snow globe. Particles of a suspension can also be filtered out. Other examples of suspensions would be dirty water, dust storms, and Italian dressing.

The particles in a colloid are very small but they are still large enough to scatter light. One has noticed the way that fog scatters headlights. Colloidal particles cannot be filtered. They are small enough to pass through filters with the fluid that supports them.

A homogeneous mixture is a solution.

A pure substance is always homogeneous with a fixed composition: Each sample of a pure substance has the same characteristic properties. Every sample of a pure substance has a fixed composition with the same formula.

All substances are chemicals and no chemical is 100 percent pure. They may be ranked as below according to decreasing purity. ACS American Chemical Society USC United States Pharmacopoeia CP Chemically Pure NF National Formulary FCC Food Chemical Code Technical

Elements

Imagine going into a large super store and the aisles have no labels. In fact, the groceries are mixed with the auto parts and the clothing. The cds and the dvds are with the toys and the outdoor items are displayed with the toys. And, the greenhouse is a bluehouse. What a mess! This was the chemist’s situation in Over 60 elements had been discovered, but there was no arrangement for them. It was hard to use them because they weren’t organized. In the 1860’s, a Russian, Dimitri Mendeleev, began looking for patterns to organize the elements. He recorded the properties of the elements on cards and then tried arranging the cards in different ways. After much thought and work, he discovered that there was a repeating pattern of properties when the elements were arranged according to their atomic mass. Mendeleev called this regular pattern of repeating properties periodic and soon the arrangement was referred to as the periodic table.

Rows across the periodic table are called periods. Columns on the periodic table are called groups and have similar chemical characteristics.

The elements to the left of the stair step line on the periodic table are metals. Hydrogen is an exception. As we have studied before, metals are mostly solid elements that are rather dense with high tensile strength. They conduct heat and electricity and are malleable and ductile. Metals have a lustrous surface.

Nonmetals are found to the right of the stair step line and lack the qualities of metals.

The metalloids such as boron, silicon, tellurium, and germanium are sometimes called semiconductors. They have some of the properties of metals and nonmetals. The noble gases make up group 8.