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🧪 ap chem


⚛️ Unit 1

  •  ⏱️4 min read

1.8 Valence Electrons and Ionic Compounds

Dalia Savy

dalia savy

⏱️ September 18, 2020


Recap from previous guides

  • Valence electrons are the outermost electrons.

  • Valence electrons are found in the s and p orbital of the outermost shell.

  • A gap in ionization energies could tell us how many valence electrons an element has.

What to know before bonding

Valence Electrons

From the periodic table, you could tell how many valence electrons an element has.

Image Courtesy of ck12

From just the periodic table, you could tell that oxygen has 6 valence electrons and carbon has 4 valence electrons. This layout of the periodic table is also proof that elements in a group have very similar properties. Therefore, they tend to bond with similar elements and form similar compounds.


Before getting into bonds, it is also good to memorize the charges of most elements on the periodic table.

Image Courtesy of Chemistry Land

The transition metals aren't included here because they have various charges and very different properties. Don't worry though, the AP won't question you about them. At most, you would have to write their electron configurations.

Types of Elements

There are three different types of elements: metals, nonmetals, and metalloids.

Image Courtesy of ck12

Metals are good conductors of heat and electricity🔥⚡, shiny, malleable (can bend), and ductile (can be made into a wire).

Nonmetals are the complete opposite: bad conductors of heat and electricity and brittle.

Metalloids have properties of both metals and nonmetals.

Types of Bonds

Elements bond to achieve the lowest possible energy, where they are stable. There are two different types of bonds you should know: ionic bonds and covalent 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.

Image Courtesy of Study

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.

Image courtesy of Wayne Breslyn

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

Check your Understanding

Try these little questions on your own and see how you do! It's just to see how well you understood this key topic :)

  1. Atoms of Ca combine with atoms of Br to form an ionic bond.

    1. What ratio would they combine in?

    2. What other compounds have this same ratio with Ca?

  2. What elements could form an ionic bond with sulfur?


  1. The compound: CaBr2 - This is because Ca has a +2 charge and Br has a -1 charge. In order for the two to bond together and form a neutral compound, there must be two Br atoms.

  2. We need other elements that have a -1 charge in order for them to bond in this 1:2 ratio with calcium. This includes all of group 17 on the periodic table, which includes fluorine, chlorine, bromine, and iodine.

  3. In a 1 to 1 ratio, any elements in group 2 would form an ionic bond with sulfur. Some examples include MgS, CaS, and BaS. In a 2 to 1 ratio, any elements in group 1 would form an ionic bond with sulfur. An example includes Na2S.

🎥Watch: AP Chemistry - Valence Electrons and Ionic Compounds

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