Chapter 15 &16 Bonding

Why Atoms Combine Most of the matter you see around you is formed by multiple compounds and mixtures. There is some matter that is in the form of elements. Can you name some? Oxygen: present in the air Iron: found in dirt and sand as iron fillings Compounds have properties that are different than their elements. ex: what are the properties of Sodium? it is a metal, solid, soft, very reactive ex: what are properties of Chlorine? it is a gas, green, nonmetal What are the properties of Sodium Chloride? White to clear in color, hard, solid, not very reactive, not poisonous to ingest.

Examples of elements and their compounds Sodium chloride Sugar CFC’s Can you name the different elements and their properties? Now name the compounds properties.

Chemically stable atoms An atom is chemically stable if its outer energy level is completely filled with electrons. Which group of the periodic table is the only group with all chemically stable atoms? Group 18 or 8A: The Noble Gases Ex: Each Noble gas has eight electrons in their outer shell. This is called the Octet Rule. Octet Rule says that all elements would like to have eight electrons in their outer shell.

Section 15.1 Valence Electrons: the electrons in the highest occupied energy level of an element’s atoms. You can find the number of valence electrons by the group number. Ex: group #3A = 3 valence electrons Ex: group 15 or 5A has 5 valence electrons

Variable Oxidation States 1+ 3- 2- 2+ 3+ 4+ 1- Variable Oxidation States

Below is an example of a Carbon atom. It has 4 valence electrons in it’s outermost energy level

Electron Dot Diagram Diagrams that show valence electrons as dots. The element symbol is written with the number of valence electrons drawn around it. The first dot should be placed at 12 O’Clock then add one dot at a time in a clockwise fashion. If there is one electron place it on the right side of the symbol. If there is two electrons place them on the right and left side of the symbol.

Any single electrons are “unpaired” electrons Any single electrons are “unpaired” electrons. Two electrons on one area is said to be “paired”

These unpaired electrons might make two single covalent bonds, as is the case in water (H2O).  Or, they might make one double covalent bond, as the case of magnesium oxide (MgO).  When Lewis dot diagrams are used for compounds, "x's" are often used to substitute for the dots of one or more elements in order to show which electrons came from which element. 

Hydrogen and Oxygen to form Water

Transition Metals are variable

Electron configurations for cations Remember a cation loses electrons and becomes more positive. Normal config for Na: 1s22s22p63s1 Cation config: 1s22s22p6 Note 1 electron missing ! The 3s orbital is gone!!!

Electron configurations for anions Remember to form an anion an atom gains electrons! Electron confg of Cl: 1s22s22p63s23p5 Anion conf: 1s22s22p63s23p6 Note change in number of “P” electrons

Review of Bonding Types Ionic Bonding Covalent Bonding Metallic Bonding Polar Covalent Bonding

Ionic Bonds: One big greedy thief dog Ionic Bonds: One big greedy thief dog! Ionic bonding can be best imagined as one big greedy dog steeling the other dog's bone.  If the bone represents the electron that is up for grabs, then when the big dog gains an electron he becomes negatively charged and the little dog who lost the electron becomes positively charged.  The two ions (that's where the name ionic comes from) are attracted very strongly to each other as a result of the opposite charges.

Formation of ionic compounds Anions and Cations have opposite charges. They attract one another by electrostatic forces. The forces of attraction that bind these oppositely charged ions are called ionic bonds. Usually the metal is giving up its electron(s) to the nonmetal.

Covalent Bonds: Dogs of equal strength Covalent Bonds: Dogs of equal strength. Covalent bonds can be thought of as two or more dogs with equal attraction to the bones.  Since the dogs (atoms) are identical, then the dogs share the pairs of available bones evenly.  Since one dog does not have more of the bone than the other dog, the charge is evenly distributed among both dogs.  The molecule is not "polar" meaning one side does not have more charge than the other.

Molecules and Covalent Bonds: Most atoms become more chemically stable by sharing electrons, rather than by losing or gaining electrons. Neutral particles formed as a result of electron sharing are called molecules A bond that forms between atoms when they share electrons is known as a COVALENT BOND.

Polar Covalent Bonds: Unevenly matched but willing to share Polar Covalent Bonds: Unevenly matched but willing to share. These bonds can be thought of as two or more dogs that have different desire for bones.  The bigger dog has more strength to possess a larger portion of the bones.  Sharing still takes place but is an uneven sharing.  In the case of the atoms, the electrons spend more time on the end of the molecule near the atom with the greater electronegativity (desire for the electron) making it seem more negative and the other end of the molecule seem more positive.

Polar and Nonpolar Molecules Polar Molecule: one that has a positive end and a negative end Note the picture below: one end of the molecule is negative (red) and the other end is positive (blue)

Here is an animation of a polar molecule forming Here is an animation of a polar molecule forming. Notice that at one end of the molecule it is + and the other end of the molecule is -

Non-polar molecules: a molecule that does not have oppositely charged ends. Both ends are either +, or, - Note in the diagram the molecules are the same. They come together and form a non-polar compound. Examples: N2 Nitrogen gas occurs as 2 Nitrogen molecules bonded together forming a non-polar molecule.

This is an example of atoms coming together and forming a POLAR MOLECULE. Watch the interactions between the + atoms and the – atoms.

Metallic Bonds: formed by the attraction between positively charged metal ions and the electrons around them. Metallic Bonds:  Mellow dogs with plenty of bones to go around These bonds are best imagined as a room full of puppies who have plenty of bones to go around and are not possessive of any one particular bone.  This allows the electrons to move through the substance with little restriction.  The model is often described as the "kernels of atoms in a sea of electrons."

Metallic Bonds & Properties Metals are made of closely packed cations rather than neutral atoms. The cations are surrounded by mobile valence electrons which can drift freely from one atom to the next.

Bond Dissociation Energies The total energy required to break the bond between two covalently bonded atoms. See table16.3 pg448

Lewis Structures Again! Resonance Structures: structures hat occur when it is possible to write two or more valid electron dot formulas that have the same number of electrons pairs for a molecule or ion.

Exceptions to the Octet Rule Exceptions occur whenever the total number of valence electrons is an odd number. Exceptions can also occur for an expanded octet (more than 8) or a deficient octet (less than 8).

Expanded Octet Octet Deficient

Coordinate Covalent Bonds A covalent bond in which one atom contributes both bonding electrons. Ex: Ammonium ion

VSEPR Theory Because electron pairs repel, molecular shape adjusts so the valence-electron pairs are as far apart as possible! THE ELECTRONS HATE EACH OTHER!!

Trigonal Planar

BENT Unpaired electrons BENT PYRAMIDAL

Get the electrons as far away from each other as possible!!! Put your molecule in a box and use it to get the electrons as far away from each other as possible!! VSEPR Box Idea! Get the electrons as far away from each other as possible!!!

Polar Molecules One end of the molecule is slightly negative and the other end is slightly positive. A molecule with two poles is dipolar or a dipole. The element with the higher electronegativity value (or the most dots) will attract the electron for the majority of the time. This makes that end of the molecule the NEGATIVE end!

Polar Bonds A molecule can be covalent but have polar bonds in which one end of the bond is + and the other end is – d+ d- Polar Covalent Bond

The End!