Chemical Bonds Selected by the SciLinks program, a service of National Science Teachers Association. Copyright 2001. For an explanation of the significance of this logo go to: Because of the tendency of atoms to complete their outer energy shells with the stable number of electrons for each shell, atoms with incomplete shells have a tendency to gain electrons, lose electrons or share electrons. Atoms that have gained or lost electrons become ions. Ionic bonds The following animation shows how ions of sodium and chlorine are formed. The oppositely charged ions in the animation will be attracted to each other and form an ionic bond. Covalent bonds Atoms can fill their outer shells by sharing electrons. In the animation, two hydrogen atoms share each other's electrons and form a molecule of hydrogen. Covalent bonds can be nonpolar, or polar. Hydrogen bonds Polar molecules can be attracted to each other much as oppositely charged ions are. © Dr.
Types of Bonds Custom Search Bonding Links <-- Back to electronegativity Electronegativity Differences between atoms can be used to determine the type of bonding that occurs. If the difference between 2 atoms is small (less than 1.7) the bond is covalent. If the difference is large (greater than 1.7) the bond is considered ionic. Exceptions- HF is covalent not ionic (difference of 1.9) BF3 is covalent (difference of 2.0) BeF2 is covalent (difference of 2.5) Covalently bonded atoms will share their electrons in order to form a stable outer electron shell that has 8 electrons. This is called an octet of electrons. Ionic is 1 minute in. Ionic bonded atoms will transfer one or more electrons from the less electronegative element (a metal) to the more electronegative element (a nonmetal) as to achieve an octect of electrons. This results in the formation of 2 ions. The bond is a strong electrostatic attraction formed by 2 opposing ions. Chemical Demonstration Videos
Elements and Compounds Elements, Atoms, and Molecules For a more advanced list of resources on atoms, elements and compounds Elements are substances that cannot be separated into simpler substances. Salt is made up of the elements sodium and chloride. The smallest particles of matter are called atoms. Chemists use symbols to represent elements. A model of an oxygen molecule. The symbol for oxygen is O. Compounds A compound is a substance formed when two or more elements are chemically joined. Mixtures Mixtures are two or more substances that are mixed together but not chemically joined. It's All About Carbon If you have questions about climate change, please e-mail them to All Things Considered or call the show at 202-898-2395. When the subject is global warming, our mood is usually "uh-oh." Which makes sense, because a warmer Earth will lead to all kinds of disruptions and expensive adjustments that we could do without. NPR and National Geographic take a year-long journey around the globe to explore how climate is shaping people and people are exploring climate. Odd Todd But there is another way to think about all of this. What we have done here is a chemistry lesson, one that begins with the elemental cause of global warming: the behavior of the carbon atom. And since carbon atoms are rather small, we have turned our atom into a cartoon. This is the introductory segment of a five-part series that explains how carbon atoms form bonds, break apart and create the conditions that can lead to global warming. In this, the first lesson, we introduce our atom. So take a look.
DNA-RNA-Protein DNA carries the genetic information of a cell and consists of thousands of genes. Each gene serves as a recipe on how to build a protein molecule. Proteins perform important tasks for the cell functions or serve as building blocks. The flow of information from the genes determines the protein composition and thereby the functions of the cell. The DNA is situated in the nucleus, organized into chromosomes. The document has two levels, basic and advanced. Learn how to navigate in the document
Teaching the Scientific Method | ASU - Ask A Biologist How to introduce students to the scientific method Students, and sometimes even teachers, often think scientists only use the scientific method to answer science-related questions. In fact, you can apply the scientific method to almost any problem. The key is to use the elements (steps) to reduce bias and help come to a solution to the problem. The scientific method is the standard in the laboratory, but don’t be fooled by the name. One size does not fit all The scientific method consists of a number of different steps, but the order in which we apply the steps can vary. While you can reorder the steps of the scientific method, it is important to apply all the steps to reduce the impact of personal bias. Steps common to versions of the scientific method A quick Web search yields several different versions of the scientific method. Communicating what is learned The scientific method also serves as an important template for communicating results and the logic behind them. Time to play
How Cells Divide share By Rick Groleau Posted 10.09.01 NOVA Most of the time, when a cell in our bodies divides, each new cell carries a complete set of chromosomes. The cells involved with human reproduction, however, carry only half after division occurs. In this step-by-step explanation, learn about mitosis and meiosis, the two types of cell division. This feature originally appeared on the site for the NOVA program 18 Ways to Make a Baby. Background on Meiosis and Mitosis As viewed from a human perspective, nature seems to have done ingenious engineering to overcome obstacles. Asexual reproduction relies on a process called mitosis, in which the nucleus of a cell divides to create two new nuclei, each containing an identical copy of DNA. Meiosis, on the other hand, is the process by which certain sex cells are created. How exactly does meiosis halve and mix chromosomes?
Membranes Organize Cellular Complexity Membranes organize proteins and other molecules enabling the cell to run much more efficiently than if everything were floating freely. Mitochondrial membranes, for example, keep protein assembly lines together for efficient energy production. And the lysosome safely holds enzymes that would destroy essential proteins if released into the cytoplasm. Real life complexity inside an insulin-producing pancreas cell. Image courtesy of Dr. Phospholipids provide the framework for all membranes in the cell. When phospholipids are placed into water, they organize themselves into a structure called a bilayer. The shape and chemical nature of phospholipids drives them to organize themselves one level further. Phospholipid membranes form a barrier that most molecules cannot cross. The nuclear pore complex (see scanning electron micrographs at right) is a unique protein structure that controls traffic flow in and out of the nucleus.
Science Classroom Science Discovery Days (Student worksheets provided) Scientific Method Unit & Safety Rules (Unit notes, worksheets, and lab ideas provided) Consumer Challenge (Student worksheets provided) Old Wives Tales Investigation (Student worksheets provided) Silly Science (Classification) (Student worksheet provided) Mystery Bags Film Canister Fun Bioglyphs (Student worksheets provided) Pottery Pieces Innovative Inventions - Internet project (Sites from the Kid Zone) (Student worksheet provided) Inventor's Challenge - Internet project (Sites from the Kid Zone) (Student worksheet provided) A Journey Through Time -Internet project (Sites from the Kid Zone) (Student worksheet provided) Science A to Z Puzzle (Student worksheet provided) Super Scientist Challenge (Student worksheets provided) Also check out ... Metric Mania - An assortment of lessons and links for the metric system! | Back to top | Science Discovery Days (T. The response from my students has been very positive! Mrs. Mrs.
Parts of the Cell - Cells Alive! For life all cells have basic needs. Cells have diverged in their structure and function to accommodate these survival requirements. Here are some KEY TERMS to help you think, explore and search for similarities and significant differences that have become the characteristics of eukaryote (animal, plant) and prokaryotic (bacteria) cells. Examples might be searching: eukaryote prokaryote reproduction or animal plant cell energy. Reproduction / cell division Energy trapping, storage and consumption Form / shape / structure Cell specialization Compartmentalization of cell functions Communication within and beyond the cell Cell / organism survival