Ionic & Metallic Bonding Chapter 7

How are ions formed? An ion is an atom that has lost or gained electrons BUT, not just ANY electrons… valence electrons! VALENCE ELECTRONS – electrons in the highest occupied energy level of an element’s atom Valence electrons are the only electrons used in chemical bonds

How do you find valence electrons? To find the valence electrons for a representative element (A Groups), look at the group number. Periodic Table Group Valence Electrons Group 1A (Alkali metals) 1 Group 2A (Alkaline Earth metals) 2 Group 3A (13) Boron Family 3 Group 4A (14) Carbon Family 4 Group 5A (15) Nitrogen Family 5 Group 6A (16) Chalcogens 6 Group 7A (17) Halogens 7 Group 8A (18) Nobel Gases 8

How do you find valence electrons? To find the valence electrons of transition elements (B Groups), look at the electron configuration. Element Electron Configuration Valence Electrons Zn [Ar] 4s2 3d10 2 Ag [Kr] 5s14d10 1 Remember that the number of valence electrons for transition elements CAN change!

Ions Two types of ions: Cations - formed when an atom loses its valence electrons Positively charged ion (more protons than electrons) Anions - formed when an atom gains valence electrons Negatively charged ion (more electrons than protons)

Naming Ions Cations: Anions: Metals are always cations The name of a cation is the same as that of the originial atom EXAMPLE: Na - sodium atom; Na1+ - sodium ion Anions: Nonmetals are always anions The name of an anion always ends in -ide EXAMPLE: F - fluorine atom; F1- - fluoride ion

Ion Formation Equation Equations to show the transfer of electrons: Na Na1+ + 1 e- Sodium atom yields sodium ion plus one electron. O + 2 e- O2- Oxygen atom plus two electrons yields an oxygen ion.

P Ba Zn Br Xe Practice: P3- + 3 e- Ba2+ + 2 e- Zn2+ + 2 e- + 1 e- Br1- Write an equation for the formation of an ion for the following atoms: P Ba Zn Br Xe P3- + 3 e- Ba2+ + 2 e- Zn2+ + 2 e- + 1 e- Br1- Xe0

Ionic Bonds & Ionic Compounds Electrostatic forces that hold ions together in ionic compounds Ionic compounds: Compounds composed of cations & anions total positive charge = total negative charge Electrically neutral compound CHEMICALLY combined

Examples of Ionic Compounds NaCl - sodium chloride (salt) Fe2O3 - iron (III) oxide (rust)

Octet Rule In forming compounds, atoms tend to achieve the electron configuration of a noble gas. Octet – set of 8 Both atoms in the compound WANT to have eight valence electrons in the highest energy level

How to atoms fulfill the Octet Rule in an IONIC compound? Atoms of metallic elements LOSE their valence electrons, leaving a complete octet in the next lowest energy level. Example: Sodium (Na) Has 1 valence electron (Group 1A) Has a total of 11 electrons 3 Energy Levels: 1st energy level: 2 electrons 2nd energy level: 8 electrons 3rd energy level: 1electron When it loses its 1 valence electron, it will be left with 8 in the next lowest energy level.

How to atoms fulfill the Octet Rule in an IONIC compound? Atoms of some nonmetallic elements tend to GAIN electrons to achieve a complete octet. Example: Chlorine (Cl) Has 7 valence electrons (Group 7A) Has a total of 17 electrons 3 Energy Levels: 1st energy level: 2 electrons 2nd energy level: 8 electrons 3rd energy level: 7 electrons When it gains 1 valence electron, it will be have a total of 8 valence electrons in the highest energy level.

Fulfilling the Octet Rule When a cation (metal) and an anion (nonmetal) combine to form an ionic compound, they both achieve a noble gas electron configuration. Example: NaCl – Sodium Chloride (Salt) Na must lose 1 electron while Cl must gain 1 electron Therefore: NaCl is made up of a Na1+ ion & a Cl1- ion Electron Configurations: Na1+ (10 electrons) - 1s22s22p6 (Same as Neon) Cl1- (18 electrons) - 1s22s22p63s23p6 (Same as Argon)

Ionic Compounds A Chemical Formula represents the composition of substances by showing the kinds and numbers of atoms in the smallest representative unit of a substance. Ca + Br  Ca2+ + Br1-  CaBr2 Mg + O  Mg2+ + O2-  Mg2O2  MgO

Forming Ionic Compounds 1. Determine the oxidation number for each element or ion in the compound. 2. Cross the numbers to become the subscripts and drop the + or – sign. 3. Reduce subscripts if possible. Beryllium + Sulfur Be  Be2+ S  S2- Be2+ S2-  Be2S2 Be2S2 reduces to Be1S1 Compound: BeS

Practice: Lithium + Selenium Potassium + Fluorine Li1+ Se2-  Li2Se Write the formula for combining the following elements: Lithium + Selenium Potassium + Fluorine Calcium + Nitrogen Strontium + Oxygen Li1+ Se2-  Li2Se K1+ F1-  KF Ca2+ N3-  Ca3N2 Sr2+ O2-  Sr2O2  SrO

What about with Polyatomic Ions? Polyatomic ions have a specific charge! Use your reference tables. You cannot change the subscripts that are with a polyatomic ion – you must put it in (parentheses)! Example: Calcium + Hydroxide Ca2+ + OH1- If you DON’T use the parentheses around the OH then you only have 1oxygen and 2 hydrogen's Ca(OH)2

Ionic Compounds Ionic compounds exists as a collection of positively and negatively charged ions in repeating patterns Therefore, its chemical formula refers to a ratio. A Formula Unit is the lowest whole-number ratio of ions in an ionic compound. NaCl – 1:1 ratio MgCl2 – 1:2 ratio AlBr3 – 1:3 ratio

Properties of Ionic Compounds MP: 801 oC (1074 K) Solubility in Water: 35.6 g/100 mL (0 °C) 35.9 g/100 mL (25 °C) 39.1 g/100 mL (100 °C Most are crystalline solids at room temperature. Typically have high melting points. Can conduct an electric current when melted or dissolved in water. Many are soluble in water. Example: Sodium Chloride

Bonding in Metals Metals can bond in two different ways: 1. Ionic Bonding bond between a metal (cation) and a nonmetal (anion) CHEMICAL combination of ions 2. Metallic Bonding The attraction of free-floating valence electrons for the positively charged metal ions. Occurs between two metal atoms. PHYSICAL combination of atoms

Metallic Bonding Metallic bonding explains why metals are… Good Conductors Transfers heat or electricity easily. Ductile Can easily be drawn into wires. Malleable Can be hammered or forced into shapes.

Why do metals have these properties? Their valence electrons are mobile and drift freely from one part of the metal to another. Valence electrons of metal atoms are loosely held by the positively charged nucleus. Valence electrons are released into a “SEA OF ELECTRONS” shared by all of the metal atoms.

Metals are… Because… Crystalline solids Crystal Atoms arranged in very compact and orderly patterns Crystal Regular, repeating arrangements of atoms, ions, or molecules Because… This arrangement helps save space while allowing as many atoms to be stacked as possible.

Shapes of Metals Simple Cube Body-centered cubic Face-centered cubic Hexagonal close-packed

Alloys Alloys are MIXTURES composed of two or more elements, at least one of which is a metal. They are important because their properties are often superior to those of their component elements. Alloys are PHYSICALLY combined, meaning that they can be separated by physical means (i.e. melting).

Examples of Alloys Cast Iron Stainless Steel Brass Surgical Steel -iron & carbon Stainless Steel -iron, chromium, carbon, & nickel Brass -copper & zinc Surgical Steel -iron, chromium, nickel, & molybdenum Sterling Silver -silver & copper

REVIEW: What is an ionic compound? What are the two types of ions? What are the characterisitics of ionic compounds? How do metallic bonds differ from ionic bonds? Cation + Anion Cation (Metals) – lose electrons Anion (Nonmetals) – gain electrons High melting points Soluble in water Conduct electricity when melted or dissolved in water Crystlline solids at room temp. Metallic bonds are physically combined; Ionic bonds are chemically combined.