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Unit 4: Bonding

Lesson 1: Aim and Objectives Aim: Why do elements form bonds? Objectives: 1.Learn the benefit for atoms to join with other atoms. 2.Learn how to determine the ratio of atoms in a bond by determining how many e- are needed to reach an octet.

Refresher: What Chemistry words can be used to describe these particles? AB C Which diagram(s) shows particles with atoms that are bonded together?

Octet Rule 8 = maximum number of valence e- Max. # valence e- = stability = low energy Everything wants to be in the lowest energy level possible…where have we seen this before? Atoms will move toward most stable e- configuration…what do they have to do to reach this? Which elements have 8 valence e-? What do we know about their potential for making chemical bonds? What’s the story with H and He?

Bond Thermodynamics Based on your understanding of the octet rule, would making a bond be an exothermic process or an endothermic process? Bond making = exothermic Bond breaking = endothermic

Homework 1: How can these atoms reach an octet? Ca N C Na P F In which ratios would these atoms combine to satisfy the octet rule? Na and ClNa and FK and Br Ca and OMg and S Ca and Cl Al and Cl C and ClC and H

Lesson 2: Aim and Objectives Aim: How are the types of chemical bonds formed? Objectives: 1.Know which types of elements are involved in metallic, ionic and covalent bonding. 2.Understand the role of electrons in metallic, ionic and covalent bonds. 3.Know the properties of metals, ionic compounds, molecular compounds and network solids.

Bonding and Element Type Metallic bonds: involve only metal atoms and typically refer to bonds between atoms of the same metal. For example: all the atoms in a hunk of calcium are bonded metallically Ionic bonds: involve metal atoms bonded to non-metal atoms or bonds between polyatomic ions Covalent bonds: involve non-metal atoms, can exist as molecules (e.g., H 2 O) or network solids (e.g., diamonds, SiO 2 )

Role of electrons in bonding Atoms are bonded chemically by electrons Metallic bonds: “sea of mobile e-.” valence electrons are free to move from one atom to another. Ionic bonds: electrons move from one atom to another creating ions that are then bonded electrostatically. Covalent bonds: electrons are shared between atoms.

Exit Questions Why do metal atoms stick together? What holds together the particles in an ionic compound? What holds together the particles in an covalent compounds?

Homework A.Make a list of properties for the following: Metals, Ionic Compounds, Molecular Substances, Network Solids B.Determine which type of substance the following is based on the provided properties. 1.Crystalline solid, high melting point, conducts electricity in aqueous and liquid form 2.Molecular solid, low melting point, poor electrical conductor, soluble in water 3.Soluble in water, high melting point, does not conduct electricity in solid form 4.Molecular gas, low boiling point, insoluble in water 5.Molecular solid, high melting point, poor electrical conductor, insoluble in water 6.Solid at room temperature, good conductor of electricity and heat in both solid and liquid phase, malleable and lustrous