Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 7 Section 1 Ions Valence Electrons The electrons in the highest occupied energy level. The group number of a representative element tells you the number of valence electrons. Helium is the one exception Valence electrons are the electrons used in almost all chemical bonds. Dot Structures Electron dot structures show valence electrons as dots. The number of dots for an element will be the same as its group number. Ex.= H· ·Mg· Octet Rule Atoms try to get a set of eight electrons when they form compounds. Atoms of groups 1,2,3 will try to lose valence electrons to leave a complete octet in the next highest energy level. Atoms of groups 5,6,7 will try to gain electrons to fill their highest energy level with an octet. Cations The loss of valence electrons by an atom produces cations (+). For metals, the name of the cation is the same as the element’s name. Na· Na+ + e – A sodium atom will ionize into a sodium(+1) ion and an electron(-1) Group 1 elements form cations with +1 charges because they have one valence electron to lose. Group 2= 2+ Group 3= 3+ Transition metals (group B) do not always follow the octet rule. Anions An atom can gain an electron to form an anion (negative charge) The name of the anion is the name of the element with the ending –ide Chlorine- Chloride, Oxygen- oxide Groups 5,6,7 gain electrons to form anions. Chlorine has seven valence electrons. Add one electron to form an ion. Cl atom + e- Cl- ion The ions produced when halogens (group 7) gain electrons are called halide ions (F-, Cl-, Br-, I-. Oxygen has six valence electrons, add two electrons to form an oxide ion. O atom + 2e- O2- ion Chapter 7 Section 2 Ionic Bonds and Ionic Compounds Ionic Compounds Compounds composed of cations and anions. Ionic compounds are neutral Ionic compounds are held together by ionic bonds. Sodium cholride is an example. Na + Cl Na+ + Cl- Formulas A chemical formula shows the kinds and numbers of atoms in one unit of a substance. Example- Sodium chloride would have a chemical formula of NaCl. This shows the ratio of Sodium to Chloride is 1:1, this ratio is called a formula unit. Ionic Compounds Ionic compounds are usually solid crystals at room temperature. In Sodium chloride, each Na+ ion is surrounded by six Cl- ions. Each Clion is surrounded by six Na+ ions. This results in high stability and very high melting points. NaCl melts at about 800 Celsius. Coordination number The coordination number of an ion is the number of ions of opposite charge that surround an ion in a crystal. Ex- NaCl would be 6. Each Na+ ion is surrounded by 6 Cl- ions. Ionic compounds can conduct an electric current when melted or dissolved in water. Chapter 7 Section 3 Bonding in metals Metallic bonds Metals are made up of closely packed cations rather than neutral atoms. The valence electrons of metals can flow freely from one area to another. Metallic bonds consist of the attraction of the valence electrons to the positive charge of the metal cation. metals Metals are good conductors of electrical current because electrons can flow freely. Metals form crystalline structures. Metals are ductile and malleable Ductile means able to be drawn into wires. Malleable means they can be hammered or forced into shapes. Alloys Alloys are mixtures composed of two or more elements, with at least one being a metal. Most of the metals we see and use are alloys. The properties of alloys are often superior to those of the elements making them up. Bronze and steel are two common alloys. Alloys Sterling silver is 92.5% silver and 7.5% copper. It is harder and more durable than pure silver. Bronze is 7 parts copper and 1 part tin. It is harder than copper and more easily cast. Steel is the most important alloy.