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For Teachers Introduction This program reviews basic atomic theory with electron shells and how valence electrons are involved in bonding. The key concepts of the octet rule, ionization energy and electro-negativity are covered. The types of atoms involved in ionic bonding and the types of ions they form are demonstrated in detail using animations. How and why ionic crystalline compounds are formed is explained, as well as the physical and chemical properties of these substances Timeline 00:00:00 Introduction Why does bonding occur? 00:02:03 bonding 00:07:42 Credits 00:08:31 End program Related Titles All About Chemical Bonding Covalent All About Chemical Bonding Metallic Understanding Electrolysis Recommended Resources http://www.files.chem.vt.edu/rvgs/act/notes/electronegativity.html http://electronegativity.org/ http://www.chemguide.co.uk/atoms/bonding/ionic.html http://www.dbooth.net/mhs/chem/bonding.html http://library.thinkquest.org/10429/high/bonding/bonding.htm 2
Student Worksheet Initiate Prior Learning 1. Complete the table. Electron Proton Neutron Relative mass Electrical charge Position in atom 2. Explain how electrons are arranged in an atom. 3
Active Viewing Guide 1. What is the name for the outer (bonding) electrons of atoms? 2. What is the relationship between the Group an element belongs to and the number of outer electrons? 3. What must be transferred before a chemical bond is formed and a compound is formed? 4. What does this define? An atom s ability to attract additional electrons. 5. What sort of bond is formed between atoms of two elements which have large differences in electro-negativity? 6. What shape is common amongst ionic compounds such as sodium chloride? 7. Give three physical characteristics of ionic compounds. 8. compounds do not conduct electricity in the solid state. When can they conduct? 4
Extension Activities 1. Discuss why electro-negativity changes as you go across a Period and down a Group. 2. On the diagram, show how electron transfer occurs between the two atoms and the resulting ions formed. 3. Discuss how the ions are arranged in a sodium crystal lattice. 5
Suggested Student Responses Initiate Prior Learning 1. Complete the table. Electron Proton Neutron Relative mass 1/1800 1 1 Electrical charge -1 +1 0 Position in atom In shells/orbits In nucleus In nucleus 2. Explain how electrons are arranged in an atom. Böhr s model shows them arranged in concentric shells (orbits) around the nucleus. There are a maximum of two electrons in first shell and a maximum of eight in the outer shell. Active Viewing Guide 1. What is the name for the outer (bonding) electrons of atoms? Valence 2. What is the relationship between the Group an element belongs to and the number of outer electrons? Group number is the same as that of outer electrons 3. What must be transferred before a chemical bond is formed and a compound is formed? Electrons 4. What does this define? An atom s ability to attract additional electrons. Electro-negativity 5. What sort of bond is formed between atoms of two elements which have large differences in electro-negativity? 6. What shape is common amongst ionic compounds such as sodium chloride? Crystal lattice 7. Give three physical characteristics of ionic compounds. Solid (high melting points) Hard Brittle 8. compounds do not conduct electricity in the solid state. When can they conduct? When molten or in aqueous solution. 6
Extension Activities 1. Discuss why electro-negativity changes as you go across a Period and down a Group. The nucleus attracts other electrons and the greater the charge on the nucleus the greater the attraction. The atom s own electrons shield the nucleus, the greater the number of shells, the greater the screening. As you go across a period, the charge on the nucleus increases, but number of shells stays the same so attraction (EN) increases. As you go down a Group, although the charge on a nucleus increases, this is outweighed by the increased number of shells/ 2. On the diagram, show how electron transfer occurs between the two atoms and the resulting ions formed. 3. Discuss how the ions are arranged in a sodium crystal lattice. Each positive sodium ion (cation) is surrounded by six negative chloride ions (anions). Each chloride ion is surrounded by six sodium ions. 7