Chemical Bonds

Chemical Bonds

Learners can:

• use Lewis structures to model valence electrons

• identify the number and type of atoms present in a chemical formula

​So........ we have been learning about chemical reactions where atoms bond with each other.

Why do you think atoms like to bond with each other?

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​The periodic table arranges elements according to their properties. The chart consists of:

• rows called periods; and

• columns called groups.

Elements in the same period or the same group have common characteristics.

​Valence Electrons

An atom contains protons, neutrons, and electrons. The protons and neutrons are located in the solid nucleus in the center of the atom. The electrons orbit the nucleus in the space called the electron cloud. Electrons travel around the nucleus in layers called energy levels. A valence electron is an electron in the outermost energy level of an atom.

​How many valence electrons do each of these elements have?

​The periodic table is arranged so that elements with similar properties are in the same column. One of those properties is the number of valence electrons in an atom of an element. The elements in a column all have the same number of valence electrons.

Valence electrons are the electrons in the outside energy level of an atom. The number of valence electrons in an atom of an element is related to its group number.

• Groups 1 and 2 have the same number of valence electrons as the group number.

• Groups 13 through 18 have a number of valence electrons equal to the group number minus 10.

​Let's practice this!

​Element Stability and the Octet Rule Video

​Atoms satisfy the octet rule by either gaining or losing electrons to make a complete outer shell.

• If the number of valence electrons is less than 4, the element will typically lose electrons.

• If the number of valence electrons is greater than 4, the element will typically gain electrons.

Atoms that gain or lose electrons form ions, or atoms with a positive or negative charge.

What would fluorine and lithium like to do with their valence electrons? Gain or lose?

A Lewis structure, or a Lewis diagram, is a model that shows the valence electrons surrounding the symbol for an element. Lewis structures are useful models because they help show why and how elements form chemical bonds.

To draw a Lewis model, follow these steps.

1. Write the symbol of the element.

2. Find the number of valence electrons using the group number.

3. Place dots to represent valence electrons. Place 1 dot on each side of the symbol (above, right, below, and left) until no valence electrons remain.

4. If there are more than 4 valence electrons, create pairs with the remaining dots.

Draw

Draw a Lewis Dot Structure for Sulfur!

​The diagram below shows six ways to draw a Lewis diagram for sulfur. Each of the diagrams is a correct model. Note that each diagram contains 2 pairs of valence electrons and 2 single valence electrons.

​Valence Electrons & Lewis Diagrams

Multiple Choice

Which of the following are valid Lewis structures for nitrogen?