Element, Mixtures, & Compounds Notes Chapter 5

Elements, the simplest substances An element is a pure substance that cannot be separated or broken down into simpler substances by physical or chemical means that still has the characteristic properties of that matter. Elements are pure substances… A pure substance is a substance where all of the “building-block” particles are identical. In an element the building blocks are called atoms. The particles in a pure substance are alike no matter where the substance is found.

Grouping Elements Elements are grouped in three main categories based on their shared properties. The groups are metals, nonmetals, and metalloids Not all the properties of each group is shared by all the group members but they do have many properties in common. By knowing the category to which an unfamiliar element belongs, you can predict some of the element’s properties.

Metals Physical properties of metals: Chemical properties of metals: Solid @ room temperature (20C) Shiny, luster Malleable Ductile Conduct heat & electricity Some are magnetic Chemical properties of metals: Some react with acids to form H2 gas Lose electrons to other atoms Corrosion – the gradual wearing away of metal due to a chemical reaction ex. rust The majority of the elements on the periodic table are metals.

Nonmetals Physical properties of nonmetals: Poor conductors of heat & electricity Dull Brittle – not malleable or ductile Chemical properties of nonmetals: Atoms usually gain or share electrons Nonmetals lack most of the properties of metals.

Metalloids (Semi-metals) Have properties of both metals & nonmetals Physical properties: Solid @ room temp Hard, but brittle Semiconductors – conduct an electrical current under certain conditions Chemical properties Somewhat reactive Act like nonmetals & take or share electrons

Compound Notes Chapter 5 – Section 2

Compounds vs. Molecules A molecule is two or more atoms chemically bonded together. A molecule can be two of the same atom bonded together (i.e. O2, H2, N2) OR two different types of atoms bonded together (H2O, CO2). All of these are molecules The bottom row are also compounds A compound has two or more atoms of two or more elements chemically bonded together. A compound is a pure substance The building block of a compound is a molecule.

Chemical Reactions Form Compounds A chemical reaction is the process by which substances change into new substances. Elements always join in a specific ratio according to their masses to form a compound. There are many different types of chemical reactions Ex: synthesis- the atoms or smaller molecules react with each other to form larger molecules or compounds. When two or more elements combine, a new compound is formed. The properties of the new compound are different from the properties of the elements that formed the compound.

Breaking Down Compounds Some compounds can be broken down into their elements. These are decomposition reactions. Example: H2O can be broken down to its elements hydrogen and oxygen Other compounds can be first broken down to form simpler compounds instead of elements. Example: Carbonic Acid (H2CO3) breaks down to CO2 and H2O which then can be broken down to its elements carbon, hydrogen and oxygen. ** The most common ways to break down a compound is through a chemical change either by adding heat or applying an electric current.

Compounds in Your World The compounds found in nature (ore) are not usually the raw materials needed by industry. These compounds must be broken down (decomposed) to provide elements or other compounds that can be used as raw materials. Example: Aluminum is used in cans and airplanes but in nature it is found as aluminum oxide (needs to be broken down) Proteins and carbon dioxide are two compounds that play an important role in living things.