Chapter 3: Matter-Properties and Changes

3.1 Properties of Matter

Substances Matter is anything that has mass and takes up space. Matter with a uniform and unchanging composition is called a substance. Also known as a pure substance

States of Matter All matter that exists naturally on Earth can be classified as one of the states of matter The three common states of matter are solids, liquids, and gases

Solids A solid is a form of matter that has its own definite shape and volume. The particles of matter in a solid are very tightly packed When heated, expands only slightly Incompressible – cannot be pressed into a smaller volume

Liquids A liquid is a form of matter that flows, has constant volume, and takes the shape of its container. The particles in a liquid are not rigidly held in place and are less closely packed than the particles in a solid. Liquid particles are able to move past each other Allows a liquid to flow and take the shape of its container Virtually incompressible Tend to expand when heated

Gases A gas is a form of matter that not only flows to conform to the shape of its container but also fills the entire volume of its container. Because of the significant amount of space between particles, gases are easily compressed. “Gas” refers to a substance that is naturally in the gaseous state at room temperature; “vapor” refers to the gaseous state of a substance that is a solid or liquid at room temperature.

Physical Properties of Matter A physical property is a characteristic that can be observed or measured without changing the sample’s composition. Density, color, odor, hardness, melting point, and boiling point are common physical properties that scientists record as identifying characteristics of a substance.

Extensive and intensive properties Extensive properties are dependent on the amount of substance present Ex: mass, length, or volume Intensive properties are independent of the amount of substance present. Ex: density A substance can often be identified by its intensive properties

Chemical Properties of Matter The ability or inability of a substance to combine with or change into one or more other substances is called a chemical property

Observing Properties of Matter Every substance has its own unique set of physical and chemical properties The particular form, or state, of a substance is a physical property, changing the state introduces or adds another physical property to its characteristics. Important to state the specific conditions under which observations are made

3.2 Changes in Matter

Physical Changes A change which alters a substance without changing its composition is a physical change. As temperature and pressure change, most substances undergo a change from one state (or phase) to another A phase change is a transition of matter from one state to another The temperature and pressure at which a substance undergoes a phase change are important physical properties – melting and boiling points.

Chemical Changes A process that involves one or more substances changing into new substances is called a chemical change. Commonly referred to as a chemical reaction The new substances formed in the reaction have different compositions and different properties from the substances present before the reaction occurred. In chemical reactions, the starting substances are called reactants, and the new substances that are formed are called products A chemical reaction always produces a change in properties

Conservation of Mass By carefully measuring mass before and after many chemical reactions, it was observed that, although chemical changes occurred, the total mass involved in the reaction remained constant. The law of conservation of mass states that mass is neither created nor destroyed during a chemical reaction – it is conserved. Mass reactants = Mass products

3.3 Mixtures of Matter

Mixtures A mixture is a combination of two or more pure substances in which each pure substance retains its individual chemical properties. The composition of mixtures is variable, and the number of mixtures that can be created by combining substances is infinite. Substances tend to mix naturally; it is difficult to keep any substance pure

Types of mixtures A heterogeneous mixture is a mixture that does not blend smoothly throughout and in which the individual substances remain distinct. Composition is not uniform A homogeneous mixture is a mixture that has constant composition throughout; it always has a single phase. Also referred to as solutions Can include solids, liquids, and/or gases (Table 3)

Separating Mixtures It is important to be able to separate mixtures into their component substances The processes used to separate a mixture are physical processes that are based on the differences in the physical properties of the substances. Heterogeneous mixtures composed of solids and liquids are easily separated by filtration. Filtration is a technique that uses a porous barrier to separate a solid from a liquid.

Most homogeneous mixtures can be separated by distillation. Distillation is a separation technique that is based on differences in the boiling points of the substances involved. A mixture is heated until the substance with the lowest boiling point boils to a vapor that can then be condensed into a liquid and collected.

Crystallization is a separation technique that results in the formation of pure solid particles of a substance from a solution containing the dissolved substance. Sublimation is the process during which a solid changes to vapor without melting Can be used to separate two solids present in a mixture Chromatography is a technique that separates the components of a mixture dissolved in either a gas or a liquid based on the ability of each component to travel or to be drawn across the surface of a fixed substrate

3.4 Elements and Compounds

Elements All matter can be broken down into a relatively small number of basic building blocks called elements. An element is a pure substance that cannot be separated into simpler substances by physical or chemical means. On Earth, over 90 elements occur naturally

Each element has a unique chemical name and symbol The chemical symbol consists of one, two, or three letters The first letter is always capitalized, and the remaining letter(s) are always lowercase As many new elements were being discovered in the early nineteenth century, chemists began to observe and study patterns of similarities in the chemical and physical properties of particular sets of elements.

In 1869, the Russian chemist Dmitri Mendeleev devised a chart which organized all of the elements that were known at the time based on the similarities and masses of the elements. Mendeleev’s table was the first version of the periodic table of elements. The periodic table organizes the elements into a grid of horizontal rows called periods and vertical columns called groups or families. Elements in the same group have similar chemical and physical properties

Compounds A compound is made up of two or more different elements that are combined chemically The chemical symbols of the periodic table make it easy to write the formulas for chemical compounds Compounds can be broken down into simpler substances by chemical means

In general, compounds that occur naturally are more stable than the individual component elements Separating a compound into its elements often requires external energy The properties of a compound are different from those of its component elements.

Law of Definite Proportions The law of definite proportions states that a compound is always composed of the same elements in the same proportion by mass, no matter how large or small the sample. Percent by mass is the ratio of the mass of each element to the total mass of the compound expressed as a percentage Percent by mass (%) = (mass of element/mass of compound) x 100

Law of Multiple Proportions The law of multiple proportions states that when different compounds are formed by a combination of the same elements, different masses of one element combine with the same fixed mass of the other element in a ratio of small whole number. Ex: water (H2O) and hydrogen peroxide (H2O2)