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Unit 4: Bonding

EQ: Why do atoms join with other atoms? EQ: How do atoms join with other atoms?

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?

A B 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• FIn which ratios would these atoms combine to satisfy the octet rule?Na and Cl Na and F K and BrCa and O Mg and S Ca and Cl Al and Cl C and Cl C 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 metallicallyIonic bonds: involve metal atoms bonded to non-metal atoms or bonds between polyatomic ionsCovalent bonds: involve non-metal atoms, can exist as molecules (e.g., H2O) or network solids (e.g., diamonds, SiO2)

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. http://www.drkstreet.com/resources/metallic-bonding-animation.swf

• Ionic bonds: electrons move from one atom to another creating ions that are then bonded electrostatically. http://www.kentchemistry.com/links/bonding/bondingflashes/bond_types.swf

• Covalent bonds: electrons are shared between atoms. http://www.kentchemistry.com/links/bonding/bondingflashes/bond_types.swf

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?

HomeworkA. Make a list of properties for the following: Metals, Ionic Compounds, Molecular Substances, Network SolidsB. 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 water5. Molecular solid, high melting point, poor electrical conductor,

insoluble in water6. Solid at room temperature, good conductor of electricity and

heat in both solid and liquid phase, malleable and lustrous