IONS

Objectives Determine the number of valence electrons in an atom of a representative element Explain how the octet rule applies to atoms of metallic and nonmetallic elements Describe how cations form Explain how anions form

Key Vocabulary Octet rule Ion Cations Anions Halide ions

Octet Rule In 1916, chemist Gilbert Lewis used the fact that noble gases are unreactive in chemical reactions to explain why atoms form certain kinds of ions and molecules He called his explanation the octet rule An octet is a set of 8 and each noble gas, except for helium, has 8 electrons in the highest energy level and a general electron configuration of ns2np6

The Octet Rule When atoms form compounds, they tend to achieve the electron configuration of a noble gas

Octet Rule Applied Atoms of the metallic elements tend to lose their valence electrons leaving a complete octet in the next lowest energy level Atoms of nonmetallic elements tend to gain electrons or to share electrons with another nonmetallic element to achieve a complete octet Most elements follow the octet rule, but there are some exceptions

Ion Formation Ion is an atom that has lost or gained a valence electron, resulting in a positive or negative charge Cation is a positively charged ion Anion is a negatively charged ion Both have an electron configuration like a noble gas

Formation of Cations A cation forms when an atom loses 1 or more valence electrons For metallic elements the name of the cation is the same as the element For example, a sodium atom forms a sodium cation Na+ Calcium forms a calcium cation Ca2+

Formation of Cations Cont. Although the name is the same, there are chemical differences between an between metals and their cations For example: Sodium metal reacts explosively with water however sodium cations are quite unreactive This is why table salt doesn’t explode in your mouth

Producers of Cations The most common cations of the periodic table are produced by metal atoms Most metal atoms have 1 to 3 valence electrons that can be easily removed We can represent the electron loss or ionization by drawing the complete electron configuration of the atom and of the ion formed

Representing Ionization Both the sodium ion and the neon atom have 8 electrons in their valence shells So it is easier to represent the process using electron dot structures

Ionization Practice Write an ionization equation for the calcium ion. Write an ionization equation for the potassium ion.

Characteristics of Stable Cations The name for the cation of a neutral atom is the same as the neutral atom Both the atom and the ion have the same number of protons and neutrons An atom and its ion have different chemical properties Ions have an electrical charge, they form compounds, and conduct electricity when dissolved in water

Stable Ions Cont. Many stable ions have noble-gas configurations Some stable ions do not have noble-gas configuration For example: Transition metals often form ions without complete octets They are also all cations

Exceptions to the Rules Ions with charges higher than 3 are rare So, some element have to form pseudo noble-gas configurations Silver, copper, gold, cadmium and mercury are elements with a pseudo noble-gas configuration

Pseudo Noble-Gas Configuration

Formation of Anions An anion is a negatively charged ion that is formed by the gaining of electrons The name of anion of a nonmetallic element is not the same as the element name The name of the anion typically ends in –ide For example: the chlorine atom becomes the chloride ion The oxygen atom becomes the oxide ion

Representing Ionization The elements that form anions have relatively full valence shells, so it is easier for them to attain noble-gas configurations by gaining electrons

Halide Ions Ions that are produced when atoms of halogens gain electrons are called halide ions All halogen atoms have 7 valence electrons and only need 1 electron to achieve a noble gas configuration All halide ions have a charge of 1-

Ionization Practice Write an ionization equation for the fluoride ion. Write an ionization equation for the oxide ion.