1.8: Valence Electrons and Ionic Compounds

Learning Targets/Content Objectives:

• I can predict formation of chemical bonds between ions by looking at their valence electrons and their reactivity.

• I can relate reactivity of an atom to its electron configuration and the valence electrons.

Vocabulary:

Valence shell- valence electrons- charge- ion- cation- anion- bond- covalent bond- ionic bond- metals- nonmetals- metalloids- polar covalent bond- non-polar covalent bond.

The number of electron in the outermost shell of an atom determines the atom reactivity, or tendency to form chemical bonds with other atoms. this outermost shell is known as the valence shell of the atom and electron in that shell are called valence electrons.

Types of Elements

there are three types of elements: metals, nonmetals and metalloids or some times called semi-metals.

types of bonds

Ionic Bonds:

Ionic bonds are formed by the transferring of electrons from one atom to another, usually a metal and nonmetal. The atom that loses an electron will gain a positive charge and is called a cation (usually a metal). The atom that gains an electron will gain a negative charge and is called an anion (usually a nonmetal). Some properties of ionic compounds include very strong bonds, solubility in water, and the ability to strongly conduct heat and electricity.

Example - NaCl

In the ionic compound NaCl, Sodium (Na) loses an electron and gains a positive charge, while Chlorine (Cl) gains an electron and therefore obtains a negative charge.

The one valence electron that was in Na was transferred to the chlorine atom in order for both ions to have a full octet. Group 1 elements and group 17 elements (halogens) often bond this way to reach stability.

When they become ions, their electron configuration actually matches the one of the noble gas closest to it. Here is an example:

Covalent Bonds

Covalent bonds are formed when atoms share electrons (usually two nonmetals).

Some properties of covalent bonds include low melting points and weak electroconductivity abilities.

There are actually two types of covalent bonds: polar covalent bonds and nonpolar covalent bonds.

• Polar covalent bonds are a type of bonding where electrons are unequally shared between two different nonmetals.

• Nonpolar covalent bonds are a type of bonding where electrons are equally shared between, usually, two of the same nonmetal.

Polar Example - HF

Hydrogen and Fluorine create a polar covalent bond. Fluorine attracts electrons more strongly due to its high electronegativity, resulting in an unequal distribution of electrons.

The dash represents two shared electrons. Rather than a transfer of electrons, Hydrogen is sharing one electron and Fluorine is sharing one electron to lead to two full octets.

Nonpolar Example - Cl2

In the covalent compound Cl2, Chlorine atoms bond together to share the final electron that they need to become noble gases.

They are both sharing one electron with each other to obtain the full octet but a non-polar covalent bond is different since their electronegativities are the same.

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