Chemical Bonding
Chemical Bonding is the mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together.
chemical formula. The composition of a formula is given by its chemical formula. A chemical formula indicates the relative number of atoms combined using atomic symbols and numeric subscripts H2O, C6H12O8, FeCl3, CaS, Li3P
Diatomic molecules Di = two Atomic = atoms two atoms Diatomic molecules contain only two atoms. F2 H2 NaCl
Learn the following diatomic elements Cl2 Br2 I2 At2 H2 O2 N2 HalHON All the hologens plus Hydrogen, Oxygen and Nitrogen
Lewis Structures Lewis Structures only show the valence electrons. Write the element symbol C
Lewis Structures Place one dot to the right of the symbol C
Lewis Structures Then add the next electron below the symbol C
Lewis Structures The next electron goes to the left C
Lewis Structures Continue moving around the symbol until all electrons have been added. N
Lewis Structures Using electron dot diagrams, a diatomic molecule of hydrogen can be represented as H H B period ¼
Write the Lewis Structures for the following elements Li Be B C N O F Ne
Lewis Structures are useful in seeing where an atom is willing to make a bond Atoms can not bond when electrons are paired
Helium has full shell with two electrons So it is written
N has 5 valence electrons N: It can only bond in three spots
Chemical Bonding There are several types of bonds – Ionic Covalent Metallic
Covalent bonds Covalent bonds are when nonmetallic elements share an electron pair. Nm + Nm
This can be two hydrogen atoms, H2 or many different elements such as in sucrose (C6H12O6)
Molecular compound Molecular compound is the simplest unit for molecules. Remember that only the valance electron are involved in bonding. A molecule is a neutral group of atoms that are held together by covalent bonds. Atoms share electrons
Covalent bonds are when nonmetallic elements share an electron pair. Nm + Nm 1s 2s 2p F . F . F F F F This is the octet rule for covalent bonding.
There are several types of covalent bonds. Polar Nonpolar Coordinate They tell how well elements share electrons
Polar Covalent is a covalent bond that does not share the electrons equally. One side is slightly + and the other is slightly – Because there are two poles of charge involve, the bond is a dipole. H O
A dipole caused by the polar covalent bond of the water molecule
Nonpolar Covalent is a covalent bond where the electrons are evenly shared. F F
Electronegativity! So how do we know what type of bond we have? Covalent Nonpolar Polar Ionic E 0-0.3 0.3-1.7 1.7-3.3%
Sulfur’s electronegativity is 2.5 Hydrogen’s electronegativity is 2.1 Use the electronegative difference to determine the bond type. The electronegativity can be found on the periodic table Sulfur and Hydrogen Sulfur’s electronegativity is 2.5 Hydrogen’s electronegativity is 2.1 S – H = 2.5-2.1 = 0.4 Where does it fall? Polar covalent
Which element is least negative? So it is written first in the formula
Try some more F2 or F – F, SF4, LiF Compound F2 SF4 LiF Electronegativity Difference Type of Bond
The HF (Hydrofluoric) can be written: + - + - H – F HF The '+' and '-' symbols indicate partial positive and negative charges.
Coordinate covalent bond is a bond formed when one atom provides both electrons in a shared pair. H N H H
How do we know if a double or triple bond in needed? Using the equations to correctly draw the Lewis Structure and Structural Formula for each of the following. All Single Bonds 6(N) + 2 = VE N= number of atoms (not counting H) VE = # of valence electrons
No interaction between atoms p+ e- p+ e-
Attraction begins p+ e- p+ e-
Covalent bond forms p+ p+ e-
Network Solids "Covalent Crystals" (crystal is used to describe Ionic structures) (Diamonds) Hard Good insulators Transparent High Melting Point
Properties of Covalent Compounds These are poor conductors of electricity in the fused or dissolved state Nonelectrolytes-do not conduct electricity in water Poor conductors of heat and electricity Brittle or cleave rather than deform
Covalent Compounds Exist as neutral molecules (C6H12O2) Solids, liquids, or gases (C6H12O2(s), H2O(l), CO2(g)) Lower melting and boiling points (i.e., often exist as a liquid or gas at room temperature)
Covalent Compounds Relatively weak force of attraction between molecules Remain as same molecule in water and will not conduct electricity H2O(l), C6H12O2(s) → C6H12O2(aq)
Naming Covalent Compounds All covalent compounds have two word names. The first word is the first element in the formula and the second corresponds to the second element in the formula except that "-ide" is substituted for the end.
Rules for Naming Binary Covalent Compounds A binary covalent compound is composed of two different nonmetal elements. For example, a molecule of chlorine trifluoride, ClF3 contains 1 atom of chlorine and 3 atoms of fluorine.
Rules for Naming Binary Covalent Compounds Rule 2. The second element in the name is named as if it were an anion, i.e., by adding the suffix -ide to the name of the element.
Rules for Naming Binary Covalent Compounds Rule 3. If both elements are in the same group, the element with the bigger period number is written first in the name. So , BrF is named “bromine fluoride", because bromine is the first element and fluorine is the second element.
Rules for Naming Binary Covalent Compounds Rule 4. Greek prefixes are used to indicate the number of atoms of each nonmetal element in the chemical formula for the compound. Exception: The only time “mono” is used is with oxygen
Naming Covalent Compounds If there is more than one atom of an element in a molecule, we need to add prefixes to these words to tell us how many are present. Here are the prefixes you'll need to remember:
mono- (use only for oxygen) Prefixes for Covalent Number of atoms Prefix 1 mono- (use only for oxygen) 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa- 9 Nona- 10 Deca-
Naming Practice SH2 P2S3 C4F10 NO sulfur dihydride diphosphorous trisulfide tetracarbon decafluoride nitrogen monoxide
Some important exceptions To the naming scheme occur because the compounds were originally named before the methodical naming scheme above became widespread. Nowadays, these names are so common that they're officially recognized: H2O is "water" NH3 is "ammonia" CH4 is "methane"