5.4 - Bohr Diagrams & Types of Compounds

Question:

Label the following diagram:

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Bohr Diagrams: A Model for an Atom

The Bohr model of an atom is structured like our solar system, whereeach “orbit” is like a planetary orbit, situated at different distances fromthe centre point.

This model depicts electrons in different orbits or “energy levels”. Often,orbits are referred to as shells.

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Each shell or orbit can hold only a certain number of electrons.1 First orbit - 2 electrons2 Second orbit - 8 electrons3 Third orbit - 8 electrons4 Fourth orbit - 2 electrons

The valence shell of an atom is the outermost orbit. The electrons in thisorbit are called valence electrons.

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Examples:

Draw Bohr diagrams for the following:

1 a helium atom

2 a carbon atom

Identify how many valence electrons are present in each. Include thenumber of protons and neutrons in the nucleus.

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Practice:

Draw Bohr diagrams for the following:

1 a potassium atom

2 a nitrogen atom

Identify how many valence electrons are present in each. Include thenumber of protons and neutrons in the nucleus.

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Compounds

Recall: A compound is a pure substance made up of two or moreelements.

Elements CompoundsH H2O

C C6H12

Li KCl

The subscripts indicate how many atoms of each element is present in aparticular compound.

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Example: For each of the following compounds state the elements andhow many atoms of each are present.

1 CH4

2 C6H12O6

3 AgNO3

Practice:

1 CuCl2

2 CO2

3 FePO4

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Example: For each of the following compounds state the elements andhow many atoms of each are present.

1 CH4

2 C6H12O6

3 AgNO3

Practice:

1 CuCl2

2 CO2

3 FePO4

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Types of Compounds

A small change in the way the atoms combine can make a big difference inthe chemical and physical properties of compounds. They’re are essentiallytwo main types: ionic and molecular.

CuCl2 - Ionic compound H2O - Molecular compound

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Ionic compounds are pure substances are generally combinations ofmetals and nonmetals. Ionic compounds often have the followingproperties:

have high melting points

dissolve in water to form solutions

are solids at room temperature

Sodium (Na) Reaction of Naand Cl

Table salt (NaCl)

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Ionic bonding - how do ionic compounds combine?

Ionic compounds are held together by attractions between oppositecharged ions (like a magnetic attraction) called ionic bonds.

Recall: Ions are formed when atoms gain or lose electrons.

We can predict how many electrons certain elements will likely lose or gainby looking at our electric charge trend on the periodic table.

Example: Draw Bohr diagrams for Na and Cl. Why would they form acompound?

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Molecular compounds are generally composed of nonmetals only. Here,electrons are shared between atoms. This is called a covalent bond.Molecular compounds often have the following properties:

can be solids, liquids, or gases at room temperature

are usually good insulators, or poor conductors, of electricity

have relatively low boiling points

Examples: H2O, CH4, CO2

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Example: Determine if each of the following compounds are ionic (metals- nonmetals) or molecular (nonmetals - nonmetals).

1 MgO

2 CO

3 NaF

4 FeCl3

5 C6H14

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Practice: Determine if each of the following compounds are ionic (metals- nonmetals) or molecular (nonmetals - nonmetals).

1 CF4

2 BeO

3 Ag3N

4 CaCl2

5 SO3

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