Chapter 5 Section 1 Simple Ions Objectives Relate the electron configuration of an atom to its chemical reactivity. Determine an atom’s number of valence electrons, and use the octet rule to predict what stable ions the atom is likely to form. Explain why the properties of ions differ from those of their parent atoms.

Chapter 5 Chemical Reactivity Section 1 Simple Ions Chemical Reactivity How much an element reacts depends on the electron configuration of its atoms. For example, oxygen will react with magnesium. In the electron configuration for oxygen, the 2p orbitals, which can hold six electrons, have only four: [O] = 1s22s22p4 Neon has no reactivity. Its 2p orbitals are full: [Ne] = 1s22s22p6

Chemical Reactivity, continued Chapter 5 Section 1 Simple Ions Chemical Reactivity, continued Noble Gases Are the Least Reactive Elements Neon is a noble gas. The noble gases, which are found in Group 18 of the periodic table, show almost no chemical reactivity. The noble gases have filled outer energy levels. This electron configuration can be written as ns2np6 where n represents the outer energy level.

Chemical Reactivity, continued Chapter 5 Section 1 Simple Ions Chemical Reactivity, continued Noble Gases Are the Least Reactive Elements, continued The eight electrons in the outer energy level fill the s and p orbitals, making these noble gases stable. In most chemical reactions, atoms tend to match the s and p electron configurations of the noble gases. This tendency to have either empty outer energy levels or full outer energy levels of eight electrons is called the octet rule.

Chapter 5 Visual Concepts The Octet Rule

Chemical Reactivity, continued Chapter 5 Section 1 Simple Ions Chemical Reactivity, continued Alkali Metals and Halogens Are the Most Reactive Elements An atom whose outer s and p orbitals do not match the electron configurations of a noble gas will react to lose or gain electrons so the outer orbitals will be full. When added to water, an atom of potassium (an alkali metal) gives up one electron in its outer energy level. Then, it has the s and p configuration of a noble gas. 1s22s22p63s23p64s1 1s22s22p63s23p6

Chemical Reactivity, continued Chapter 5 Section 1 Simple Ions Chemical Reactivity, continued Alkali Metals and Halogens Are the Most Reactive Elements, continued Calcium, a halogen, is also very reactive. An atom of calcium has seven electrons in its outer energy level. By gaining just one electron, it will have the s and p configuration of a noble gas. 1s22s22p63s23p5 1s22s22p63s23p6

Chapter 5 Valence Electrons Section 1 Simple Ions Valence Electrons Potassium after it loses one electron has the same electron configuration as chlorine after it gains one. Both are the same as that of the noble gas argon. [Ar] = 1s22s22p63s23p6 The atoms of many elements become stable by achieving the electron configuration of a noble gas. The electrons in the outer energy level are known as valence electrons.

Chapter 5 Visual Concepts Valence Electrons

Valence Electrons, continued Chapter 5 Section 1 Simple Ions Valence Electrons, continued Periodic Table Reveals an Atom’s Number of Valence Electrons To find out how many valence electrons an atom has, check the periodic table. For example, the element magnesium, Mg, has the following electron configuration: [Mg] = [Ne]3s2 This configuration shows that a magnesium atom has two valence electrons in the 3s orbital.

Valence Electrons, continued Chapter 5 Section 1 Simple Ions Valence Electrons, continued Periodic Table Reveals an Atom’s Number of Valence Electrons, continued The electron configuration of phosphorus, P, is [Ne]3s23p3. Each P atom has five valence electrons: two in the 3s orbital and three in the 3p orbital.

Valence Electrons, continued Chapter 5 Section 1 Simple Ions Valence Electrons, continued Atoms Gain Or Lose Electrons to Form Stable Ions All atoms are uncharged because they have equal numbers of protons and electrons. For example, a potassium atom has 19 protons and 19 electrons. After giving up one electron, potassium still has 19 protons but only 18 electrons. Because the numbers are not the same, there is a net electrical charge.

Valence Electrons, continued Chapter 5 Section 1 Simple Ions Valence Electrons, continued Atoms Gain Or Lose Electrons to Form Stable Ions, continued An ion is an atom, radical, or molecule that has gained or lost one or more electrons and has a negative or positive charge. The following equation shows how a potassium atom forms an ion with a 1+ charge. K  K+ + e An ion with a positive charge is called a cation.

Chapter 5 Visual Concepts Ion

Valence Electrons, continued Chapter 5 Section 1 Simple Ions Valence Electrons, continued Atoms Gain Or Lose Electrons to Form Stable Ions, continued In the case of chlorine, far less energy is required for an atom to gain one electron rather than give up its seven valence electrons to be more stable. The following equation shows how a chlorine atom forms an ion with a 1− charge. Cl + e → Cl An ion with a negative charge is called an anion.

Comparing Cations and Anions Chapter 5 Visual Concepts Comparing Cations and Anions

Valence Electrons, continued Chapter 5 Section 1 Simple Ions Valence Electrons, continued Characteristics of Stable Ions Both an atom and its ion have the same number of protons and neutrons, so the nuclei are the same. The chemical properties of an atom depend on the number and configuration of its electrons. Therefore, an atom and its ion have different chemical properties.

Valence Electrons, continued Chapter 5 Section 1 Simple Ions Valence Electrons, continued Many Stable Ions Have Noble-Gas Configurations Many atoms can form stable ions with a full octet. For example, Ca, forms a stable ion. The electron configuration of a calcium atom is: [Ca] = 1s22s22p63s23p64s2 By giving up its two valence electrons in the 4s orbital, it forms a stable cation with a 2+ charge: [Ca2+] = 1s22s22p63s23p6 This electron configuration is like that of argon.

Some Ions with Noble-Gas Configurations Chapter 5 Section 1 Simple Ions Some Ions with Noble-Gas Configurations

Valence Electrons, continued Chapter 5 Section 1 Simple Ions Valence Electrons, continued Some Stable Ions Do Not Have Noble-Gas Configurations Not all stable ions have an electron configuration like those of noble gases. Transition metals often form ions without complete octets. With the lone exception of rhenium, Re, the stable transition metal ions are all cations. Also, some elements, mostly transition metals, form stable ions with more than one charge.

Stable Ions Formed by the Transition Elements and Some Other Metals Chapter 5 Section 1 Simple Ions Stable Ions Formed by the Transition Elements and Some Other Metals

Chapter 5 Section 1 Simple Ions Atoms and Ions Having identical electron configurations does not mean that a sodium cation is a neon atom. They still have different numbers of protons and neutrons. Ions and Their Parent Atoms Have Different Properties Both sodium and chlorine are very reactive. When they are mixed, a violent reaction takes place, producing a white solid—table salt (sodium chloride). It is made from sodium cations and chloride anions.

Atoms and Ions, continued Chapter 5 Section 1 Simple Ions Atoms and Ions, continued Atoms of Metals and Nonmetal Elements Form Ions Differently Nearly all metals form cations. For example, magnesium metal, Mg, has the electron configuration: [Mg] = 1s22s22p63s2 To have a noble-gas configuration, the atom must either gain six electrons or lose two. Losing two electrons requires less energy than gaining six.

Atoms and Ions, continued Chapter 5 Section 1 Simple Ions Atoms and Ions, continued Atoms of Metals and Nonmetal Elements Form Ions Differently, continued The atoms of all nonmetal elements form anions. For example, oxygen, O, has the electron configuration: [O] = 1s22s22p4 To have a noble-gas configuration, an oxygen atom must either gain two electrons or lose six. Acquiring two electrons requires less energy than losing six.