Introduction to Bonding and electron dot/lewis structures Chemistry

Why is bonding important?? Without bonding the universe would be a mass of individual atoms. The type of bond defines the properties of a substance. NaCl…shape H2O and oil…dissolving                                              

Electronegativity Ability of atoms within a molecule to attract electrons

Polar Describes a bond with an unequal distribution of electrons

Nonpolar Describes a bond with an equal distribution of electrons

Covalent Describes a bond where electrons are shared

Ionic Describes a bond where electrons are transferred

DETERMINING BOND TYPE Calculate the difference in electronegativities: > 1.7 = ionic (electrons transfer) 0.5-1.7 = polar covalent (electrons are shared unequally) <0.5 = nonpolar covalent (equal sharing of electrons)

EXAMPLE: 1. H2 a) Calculate the difference in electronegativities: 2.2 – 2.2 = 0  nonpolar covalent (equal sharing) b) Draw the electron dot/Lewis structure: H + H = H H [recall the “duet rule”—H wants 2 e-]

Nonpolar Covalent Bonds Describes a bond where electrons are shared equally Less than 0.5 electronegativity difference. Let’s look at an animation of this with H2: H2 EN=0 (http://www2.gasou.edu/chemdept/general/molecule/polar.htm) (http://web.jjay.cuny.edu/~acarpi/NSC/5-bonds.htm)

NON-POLAR COVALENT BONDS Covalent Bonds: Dogs of equal strength share equally. Covalent bonds can be thought of as two or more dogs with equal attraction to the bones.  They share equally.

NON-POLAR COVALENT BONDS Since the dogs are identical, then the dogs share the bones evenly.  Since one dog does not have more of the bone than the other dog, the bone is equally shared between both dogs. One dog does not have more than the other.

EXAMPLE: 2. H2O a) calculate the difference in electronegativities: 3.5 – 2.2 = 1.3  polar covalent (unequal sharing) b) Draw the electron dot/Lewis structure: H + H + O = H O H [recall the “duet rule”—H wants 2 e-]

Polar Covalent Bonds Describes a bond where electrons are shared unequally Electronegativity (EN) difference is between 0.5 and 1.7. Let’s look at an animation of this with H2O and HBr: H2O END=1.4 HBr END=0.7 (http://www2.gasou.edu/chemdept/general/molecule/polar.htm) (http://web.jjay.cuny.edu/~acarpi/NSC/5-bonds.htm)

POLAR COVALENT BONDS Unevenly matched dogs that are willing to share. These bonds can be thought of as two or more dogs that have different desire for bones. They share unequally.

POLAR COVALENT BONDS The bigger dog has more strength to possess a larger portion of the bones.  Sharing still takes place but is an uneven sharing. 

EXAMPLE: 3. NaF a) calculate the difference in electronegativities: 4.0 – 0.9 = 3.1  ionic (electrons are transferred) b) Draw the electron dot/Lewis structure: Na + F = Na F - +

Ionic Bonds Describes a bond where electrons are transferred. Greater than 1.7 electronegativity difference. Let’s look at an example of this with NaCl: NaCl EN=2.1 (http://web.jjay.cuny.edu/~acarpi/NSC/5-bonds.htm) (http://www2.gasou.edu/chemdept/general/molecule/polar.htm)

IONIC BONDS One big greedy thief dog! Ionic bonding can be best imagined as one big greedy dog stealing the other dog's bone. 

The bone represents the electron that is up for grabs. IONIC BONDS The bone represents the electron that is up for grabs. When the big dog gains an electron he becomes negatively charged, and the little dog who lost the electron becomes positively charged.  These two ions (that's where the name ionic comes from) are attracted very strongly to each other as a result of the opposite charges.

Electron tug-of-war analogy LOW Electronegativity HIGH Electronegativity

equal sharing  covalent bond It’s a tie… e- equal sharing  covalent bond

The non-metal is pulling harder... So what would unequal sharing be? polar covalent

Transfer of electrons  ionic bond The non-metal wins! e- Transfer of electrons  ionic bond