SCH4U - Bonds and Lewis Structures

What is the definition of a compound? (1)

• A combination of different elements in different ratios

What is the definition of a chemical bond? (1)

• Interaction between elements usually through their valence electrons

• Electrostatic forces that hold atoms together in a compound

Betwee which 2 groups of elements on the periodic table do Ionic Compouns form?

• Ionic bonds form between metals and non - metals

What are Ionic compounds defined as?

• A TRANSFER of electrons from metal to non - metal

Describe how Ionic compounds form

• Opposites attract, resulting in cations and anions to come into contact

• They experience an electrostatic force of attraction

• This results in a chemical bond known as an Ionic Bond

List some properties of Ionic Compounds

• SOLID at room temperature

• They form CRYSTALS or crystal salts

• HIGH melting points

• Highly SOLUBLE in water

• ELECTROLYTES: High electrical conductivity in molten or liquid state, but not in solid state 

Between which 2 groups on the periodic table do Covalent compounds form?

• Non - metals

What are covalent compounds defined as?

• They are defined as the SHARING of one or more pair of electrons

Describe the difference between non - polar and polar covalent compounds.

• NON-POLAR: atoms share electrons EQUALLY

• POLAR: atoms share electrons UNEQUALLY

When covalent compounds are formed, why are shared electrons pairs attracted to the nuclei of both atoms?

• They are attracted to nuclei of both atoms since opposite charges attract.

• Electrons are negatively charged while nuclei are positively charged, thus they attract.

List some properties of covalent compounds

• They can be SOLID, LIQUID or GAS at room temperature

• Relatively LOW melting and boiling points

• NOT electrolytes 

• DIATOMIC (2 atoms), TRIATOMIC (3 atoms) or POLYATOMIC (many atoms)

What criterion determine which atom is placed in the middle of a covalent comppound lewis diagram?

1. Carbon is always in the middle (due to it being able to make 4 bonds)

2. The singular atom is usually in the middle

3. In molecules that have one atom of each kind, the one that makes the most bonds or is least electronegative will be placed in the middle.

List the complete steps for drawing lewis structures of normal covalent compounds

1. Find the total # of valence e^- : (VE)

2. Find total # of electrons in the molecule: (TE)

3. Calculate the # of bonding electrons: (BE) = (TE) – (VE)

4.Calculate the number of bonds in the molecule: Bonds = BE ÷ 2

5. Distribute the bonds between atoms

6. Distribute the remaining lone pairs to give each atom the total amount of e they need to be stable.

List the 3 common exceptions to the octet rule for our course

• HYDROGEN: 2 valence e^-

• BERYLLIUM: 4 valence e^-

• BORON: 6 valence e^-

Define a polyatomic ion (in your own words, and then according to the scientific definition)

• An electrically charged species formed by covalent bonding of atoms of two or more different elements, usually nonmetals

Note the differences that would need to be made when drawing lewis diagrams of polyatomic ions

1. To find total # of valence e^-:

   1. Add 1e^-  to VE for each negative charge

   2. Subtract 1e^- VE for each positive charge

2. Place brackets around the ion and label the charge