Tham khảo tài liệu 'economic english 8', ngoại ngữ, anh ngữ phổ thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | ------------------------------------- PHYSICAL Elements that share the same period have the same number of electron shells. Common Elements Some elements are frequently encountered in biologically important molecules and everyday life. Below you will find a list of common elements their symbols and common uses. H Hydrogen involved in the nuclear process that produces energy in the sun He Helium used to make balloons fly C Carbon found in all living organisms pure carbon exists as graphite and diamonds N Nitrogen used as a coolant to rapidly freeze food O Oxygen essential for respiration breathing and combustion burning Si Silicon used in making transistors and solar cells Cl Chlorine used as a disinfectant in pools and as a cleaning agent in bleach Ca Calcium necessary for bone formation Fe Iron used as a building material carries oxygen in the blood Cu Copper a . penny is made of copper good conductor of electricity I Iodine lack in the diet results in an enlarged thyroid gland or goiter Hg Mercury used in thermometers ingestion can cause brain damage and poisoning Pb Lead used for X-ray shielding in a dentist office Some elements exist in diatomic form two atoms of such an element are bonded and are technically molecules. These elements include hydrogen H2 nitrogen N2 oxygen O2 fluorine F2 chlorine Cl2 bromine Br2 and iodine I2 . Structure and Properties of Matter Matter has weight and takes up space. The building blocks of matter are atoms and molecules. Matter can interact with other matter and with energy. These inter SCIENCE ----------------------------------- actions form the basis of chemical and physical reactions. Molecules Molecules are composed of two or more atoms. Atoms are held together in molecules by chemical bonds. Chemical bonds can be ionic or covalent. Ionic bonds form when one atom donates one or more electrons to another. Covalent bonds form when electrons are shared between atoms. The mass of a molecule can be calculated by adding the .
