Ionic Bonding

Valence electrons Valence electrons – electrons in the highest occupied energy level of an element’s atoms. Determined by looking at the group number (skipping transition metals) Helium is the only exception (two valence electrons) Electron Dot Structure’s show valence electrons as dots for a better understanding of bonding. Ex:

Octet Rule In forming compounds, atoms tend to achieve the electron configuration of a noble gas. (octet is a set of eight) Metals tend to lose their electrons to form a cation and a complete octet in the next-lowest energy level. Non-metals tend to gain electrons, or share electrons with another non-metal, to form an anion and achieve a complete octet.

Octet Rule Cl gains an electron to form an anion in an ionic bond Na loses an electron to form a cation in an ionic bond Draw orbital diagram and write electron configuration Cl gains an electron to form an anion in an ionic bond Na similar to Neon’s orbital diagram, Cl similar to Argon’s orbital diagram

Halide ions Ions that are produced when a halogen gains an electron. Ex: Cl-

Identify the Element X2+, a cation with 36 electrons X3- , an anion with 18 electrons

Bonds Ionic bonds- electrostatic forces that hold ions together in ionic compounds. result from the transfer of electrons from one element to another. Bonding between metals and non-metals Covalent bonds – Result from the sharing of electrons between two atoms. Electronegativity difference can determine the type of bond that occurs: 0-0.4 non-polar covalent 0.4-2.0 polar covalent >2.0 ionic

Properties of ionic Compounds Crystalline solids at room temperature High melting points Conduct an electric current when melted or dissolved in water. All salts are ionic.

Metallic bonds The valence electrons of metal atoms are free floating and can be modeled as a “sea of electrons” attracted to the positively charged metal ions. This explains why metals are good conductors of electricity! Electrons flow freely from one end of the metal to the other. (as electrons enter one end, they leave the other)

Alloys Alloys – mixtures composed of two or more elements, at least one of which is a metal. Properties are usually superior to those of their component elements. (Ex: Sterling silver, which contains silver and copper, is harder and more durable than pure silver)

Chemical formulas Formula Unit (chemical formula)– lowest whole- number ratio of ions in an ionic compound. Na+ and Cl- have a 1:1 ratio, so the chemical formula is NaCl

writing formulas Determine the lowest ratio of atoms to have an overall charge of zero. Write the symbol for the cation first, and the anion second. Write the subscripts of the ratio.

Crisscross method Write the symbol of the cation with it’s charge above, followed by the symbol of the anion with it’s charge above. Crisscross your charges.

Practice writing formulas Potassium Iodide Gallium Bromide Strontium Fluoride Aluminum Selenide Zinc Chloride

Naming Binary ionic compounds Anion has an ”Ide” ending NaCl MgBr2 K2S

Naming Binary compounds with transition metals Transition metals can form more than one ion, so we must identify which ion is forming the bond. This is done by adding roman numerals after the metal to represent it’s charge. Two methods to determining cation charge: reverse crisscross determine the charge based on the amount that will make the cation and anion add up to zero.

Practice Cr2O3 2. Fe2S3 3. CuO

Iron (III) Chloride Copper (I) Fluoride Cobalt (II) Bromide Write the formula Iron (III) Chloride Copper (I) Fluoride Cobalt (II) Bromide

Review Write the compound name or formula for the following ionic compounds: Copper (II) Fluoride MgBr2 Aluminum Selenide Fe2S2

Common uses of polyatomics acetate: C2H3O2-  nailpolish bicarbonate (hydrogen carbonate): HCO3-  baking soda chlorate: ClO3-  detergents cyanate: OCN-  paper cyanide: CN- plastic hydroxide: OH-  water nitrate: NO3-  drinking water perchlorate: ClO4-  fireworks carbonate: CO32- glass peroxide: O22- mouthwash sulfite: SO32- wine borate: BO33-  wood preservatives phosphate: PO43-  dairy

polyatomic ions NH4+ ammonium ion NH3+ ammonia ion OH– hydroxide ion CO3 2– carbonate ion SO4 2– sulfate ion CN – cyanide ion NO3 – nitrate ion PO43– phosphate ion

Nick the Camel ate a Clam for Supper in Phoenix -Ates Nick the Camel ate a Clam for Supper in Phoenix Consonants = # of oxygens Vowels = charge

Prefixes and suffixes Ion Name Ion Formula Meaning Persulfate SO52- One more oxygen than Sulfate Sulfate SO42- Most common ion Sulfite SO32- One less oxygen than Sulfate Hyposulfite SO22- One less oxygen than Sulfite

Polyatomic naming The anion’s name ending remains (-ate, -ite, etc.), rather than changing to –ide. You must have parentheses around the polyatomic ion if there is more than one. All other ionic naming rules apply.

Practice Naming Polyatomics NH4NO3 K3PO3 CsCO3 Al(OH)3 Fe2(SO4)3 Ba(NO3)2

Practice Writing Formulas Lithium Phosphate Barium Hydroxide Magnesium Bicarbonate Ammonium Phosphate Potassium Chlorite