Valence electron

Valence electrons are the electrons in an atom's outer shell, which is called its valence shell. The more valance electrons an atom has in its outer shell, the more stable the atom is. For example, if an atom has two valence electrons in its outer shell but can have up to eight, the atom is relatively unstable. When atoms bond to create chemical compounds, they may give up or receive valence electrons to achieve stability. For example, lithium fluoride is a chemical compound. At atom of lithium has one electron in its outer shell while an atom of fluorine has seven. When they bond, a lithium atom gives the electron in its outer shell to a fluorine atom. This makes the fluorine atom's outer shell full, so it is now stable. It also makes the lithium atom stable; because it no longer has an electron in its outer shell, which is its third shell, its second shell becomes its outer shell. This shell has the maximum number of electrons, so it is full. This is an example of ionic bonding. In covalent bonding, atoms share valence electrons to become stable.

Elements & Atoms

An element is a primary component of matter. It contains only one type of atom and cannot be broken down into a simpler substance. As of 2014, scientists have discovered 118 elements, which are listed in the periodic table.

An atom is the smallest unit of an element. Each atom has a specific number of protons in its nucleus, or center. An element's atomic number is the number of protons within the nucleus of its atoms. For example, oxygen's atomic number is eight, which means its atoms have eight protons.

An atom has the same number of protons and electrons, but its electrons orbit, or spin around, the atom's nucleus much the way planets orbit the sun. Electrons orbit in orbitals, which are commonly called shells. The first shell, the inner shell, can hold two electrons. The next shell can hold eight electrons. The first eighteen elements in the periodic table can hold eight electrons at most in the third, or outer, shell. (The elements after the first eighteen can hold more electrons in their third shell.) The electrons in this third, or outer shell, are called valence electrons.

Elements that have the same number of valence electrons in their atoms have similar chemical properties. The number of valence electrons also determines the element's position in the periodic table. The elements in the periodic table are divided into groups. Elements within a group usually have the same number of valence electrons in their outer shell. For example, most elements in group V have five valence electrons in their outer shell.

Valency

Valency is the likelihood that an element will combine with another element. An element has only one type of atom. The number of electrons in the outer shell of its atoms can be used to calculate the element's valency. Elements that are very likely to combine with other elements are said to be reactive. Reactive elements have only one or two elements in their outer shell or six or seven elements in their outer shell. Atoms in Groups I and II in the periodic table have only one or two electrons in their outer shell; atoms in Groups VI and VII have six or seven electrons in their outer shell. Elements that have atoms with only one, two, or three electrons in their outer shell are metals (with the exception of hydrogen and helium). Elements with atoms with four to seven electrons in their outer shells are non-metals.

To calculate the valency of most elements, first note how many electrons are in the outer shell of its atoms. Note that this is not the total number of electrons in its atoms. For example, an atom of sodium has eleven electrons: two in its first shell, eight in its second shell, and one in its third shell. The valency for atoms with four or fewer electrons in their outer shell is simply the number of electrons in this shell. Valency is calculated differently for atoms with five or more electrons in their outer shell. For these atoms, subtract the number of electrons in the outer shell from eight. For example, chlorine has seventeen electrons, two in its first shell, eight in its second shell, and seven in its outer shell. To determine its valency, subtract seven from eight. Chlorine has a valency of one. Elements with a low valency tend to be very reactive.

Chemical Bonds

Chemical compounds form when elements are joined by chemical bonds. These bonds are very strong—so strong that they make the compound behave like a single substance.

Two main types of bonds create chemical compounds. Ionic bondingoccurs when electrons move from one atom to another to gain stability. The atoms in sodium chloride, a chemical compound commonly known as table salt, have ionic bonds.

Covalent bonding exists when atoms in a chemical compound share electrons. The atoms in hydrogen chloride, a chemical compound consisting of hydrogen and chlorine, have covalent bonds. Hydrogen chloride is a gas used to clean metals and make dyes and fertilizers.

Generally, metals bond with non-metals to form ionic compounds, and non-metals bond with other non-metals to form covalent compounds.

Adrienne A. Kennedy

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