CH. 7 IONS WHY: Everything around us is made up of compounds and molecules. It is important to know the properties of these compounds/molecules and the impact they have on us.

Valence electrons Electrons in the highest occupied energy level of an elements atoms Electrons used in bonding Responsible for determining chemical properties of the element To find valence electrons: When dealing with representative elements, simply look at group number

Electron Dot Structure Diagrams that show the valence electrons of an element Example: see board On your own: write the electron dot structure for: Magnesium Sulfur Fluorine Potassium

Octet Rule Noble Gases are unreactive in chemical reactions (stable) In forming compounds, atoms tend to achieve the electron configuration of a noble gas (8 VE) Metallic atoms will lose valence electrons, leaving an octet in the next lowest energy level Nonmetallic atoms will gain (or share with another nonmetallic atom) valence electrons to achieve a complete octet

Cations/Anions Ion- forms when an atom gains or loses electrons CATIONS Formed when an atom loses valence electrons Metal What is the charge of a cation? Positively charged ion Name stays the same Charges?How many VE are being lost? Transition metals have special rules

Cations/Anions cont. Anions Formed when an atom gains valence electrons Nonmetal What is the charge of an anion? Negatively charged ion Name changes to end in -ide Charges?How many VE are being gained? Identify if the following form cations or anions - Ca-Ba- He - I- N- S - Zn- Co- Ar

Formation of Ionic Compounds Cation + Anion = Ionic Compound Opposites attract Metal + Nonmetal Even though ionic compounds are composed of ions, they are electrically neutral

Properties of Ionic Compounds Crystalline solids at room temperature Crystals in repeating 3-d patterns Strong attractive forces result in a high melting and boiling point –lots of energy needed to break bonds Hard and Brittle Conduct an electric current when melted or dissolved in water Often are soluble in water (can dissolve) Alloy- mixture of two or more elements, at least one of which is a metal- properties are superior to those of component elements

Bonding in Metals Metals made up of closely packed together cations Valence electrons modeled as a “sea of electrons” Valence electrons can drift from one part of metal to another Mobile Metallic Bonds attraction of free- floating valence electrons for positively charged metal ions Good conductors of electricity Malleable Ductile

Ionic Bonds Chemical Formula- shows the kinds and numbers of atoms in the smallest representative unit of a substance NaCl Formula Unit- lowest whole-number ratio of ions in an ionic compound 1:1 Electrostatic Forces that hold ions together in ionic compounds are called ionic bonds

Covalent Bond A chemical bond in which a pair of electrons are shared between 2 atoms Tug of war Molecule- group of atoms joined together by covalent bonds Molecular compound- compound composed of molecules How different from Ionic compounds?? Diatomic molecule- a molecule consisting of two atoms Must memorize : H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2

Properties of molecular compounds Lower melting and boiling points than ionic compounds Weaker bonds Many molecular compounds are gases or liquids at room temp Mostly composed of two or more non-metal atoms Generally have little to no electrical conductive properties ***Properties of molecules compounds vary greatly***

Molecular formula Shows how many atoms of each element a molecule contains Ex- Ethane= C 2 H 6 Does not show how atoms are arranged within the molecule Structural formula- represents covalent bond by dashes and shows the arrangement of covalently bonded atoms

Octet Rule Remember me???? In forming covalent bonds, electron sharing usually occurs so that atoms attain the electron configuration of noble gases Example: Water=??

Single Covalent Bond When two atoms share a single pair of electrons Examples: F 2, H 2 O, NH 3

Double Covalent Bond When noble gas configuration is achieved by sharing two pairs of electrons Example: CO 2

Triple Covalent Bond When noble gas configuration is achieved by sharing three pairs of electrons Example: N 2

Molecular orbital Atoms have atomic orbitals, molecules have molecular orbitals When two atoms are shared in these molecular orbitals, they become bonding orbitals VSEPR (Valence shell electron pair repulsion) Theory- -explains the 3-d shapes of molecules -repulsion between the electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible

Non-polar vs. Polar Bond In covalent bonds, the bonding pair of electrons are pulled in a tug or war manner Non-Polar = when the electrons in the bond are pulled equally Polar = when the electrons in the bond are pulled unequally, giving one atom a slight negative charge and the other a slight positive charge

InterMolecular attractions Van der Waals forces- weakest attractions between molecules Dipole interactions Dispersion forces Hydrogen Bond-attractive force in which a hydrogen covalently bonded to an atom is also slightly attracted to another semi- negatively charged atom Bond Strength= Ionic > Covalent > Intermolecular attractions(Van der Waals)