Chapter 5: Understanding the Properties of Elements PDF

Chapter 5: Understanding the Properties of Elements Section 5.3: The Periodic Table The Periodic Table Scientists organize information to help them make conclusions or develop new hypotheses. By the mid-1800s, chemists had discovered over 50 elements and had determined their properties. The...

Chapter 5: Understanding the Properties of Elements Section 5.3: The Periodic Table The Periodic Table Scientists organize information to help them make conclusions or develop new hypotheses. By the mid-1800s, chemists had discovered over 50 elements and had determined their properties. There was not, however, an efficient and effective way to organize the information. Mendeleev’s Arrangement In the late 1860s, a Russian chemist named Dimitri Mendeleev organized known elements, looking for patterns in properties. Mendeleev found a pattern when he placed the elements in order of increasing atomic mass (the average mass of the naturally occurring isotopes of an element). He couldn’t look at the number of sub- atomic particles since they hadn’t been discovered yet. This organization resulted in properties repeating in a pattern, or periodically. For this reason Mendeleev’s table became known as the periodic table. It is a system for organizing elements into columns and rows so that elements with similar properties are The Modern Periodic Table Today’s periodic table is based on the arrangement of the elements according to increasing atomic number. Each element has its own box that contains the information shown below. In the periodic table, most of the elements with atomic numbers less than 93 are naturally occurring. The other elements are synthetic— they have been made by scientists. The Periodic Table of the Elements  Classes of Elements in the Periodic Most elements are classified asTable either metals or non-metals. However some elements, known as the metalloids, fall between these groups. Copyright © 2010 McGraw-Hill Ryerson Ltd.  Classes of Elements in the Periodic Table Metals The metals are: Good conductors of heat (used in pots and pans) Good conductors of electricity (used in wires) Lustrous (used in jewelry and other ornamental objects) Almost all are solids (except for mercury) Malleable (can be hammered into sheets) Cover up Ductile (can be drawn into wires) Examples: Gold, Aluminum, Silver, Copper, and Sodium  Classes of Elements in the Periodic Table Non-metals The non-metals are: Poor conductors of heat (used as insulators in construction) Poor conductors of electricity (used to insulate wires) Non-lustrous (dull in appearance) Either solids, liquids, or gases (there are examples of each) Brittle in the solid state (break easily when hammered) Cover up Non-ductile (cannot be drawn into wires) Examples: Phosphorus, Sulfur, Chlorine, and Neon  Classes of Elements in the Metalloids Periodic Table Metalloids have properties of both metals and non-metals. The metalloids show the largest variance in properties of any group in the periodic table. They can be metallic or non-metallic, malleable or non- malleable. The most notable members of this group are silicon and Cover up germanium, which have brought about revolutionary changes in the semiconductor industry. (Semiconductors normally will not conduct electricity but can be induced to do so at elevated temperatures or when they are mixed with trace amounts of other elements.) Examples: Boron, Silicon, Arsenic, and Antimony  Mining for Metals The elements exist as a natural resource that we can obtain from the earth, generally by mining. Today, mining for metals such as gold relies on a great deal of chemistry. Not only do mines disrupt the land and potentially harm ecosystems, but there is a risk of harmful chemicals such as cyanide getting into the ground water and contaminating surrounding areas. Diamond mines, while economically successful, can disrupt ecologically sensitive environments. People must start to ask whether the economic benefits of mining operations outweigh the environmental damage they can cause.  Metals and Health Metals are not only important economically. They are also part of essential processes in plants and animals. Metals essential for plant and animal life include iron, copper, zinc, magnesium, and calcium. Exposure to toxic metals like arsenic, aluminum, lead, and mercury in the environment can cause harm to living things when they bioaccumulate and biomagnify. Mercury levels in the environment have increased due to human activities such as burning waste materials and fossil fuels. Aboriginal peoples who depend on fishing and hunting for their survival have been devastated by mercury poisoning from the food they eat. Metals and Health cont’d Metals are found in a vast number of consumer products; many times in products you wouldn’t know contain them.  Periods and Groups in the Periodic Table Periods are rows of elements in the periodic table. Periods are numbered from 1 to 7, moving downward. The period indicates the number of occupied shells in that row. Groups (families) are columns of elements in the periodic table. The elements in groups tend to have very similar physical and chemical properties. Groups are numbered from 1 to 18. The group indicates the number of e- The groups shown in the image above each in the outer (valence) shell. have very characteristic properties.. Group 17: Halogens Groups cont’d