C H 6 C HEMICAL B ONDING Chemistry

C HEMICAL B ONDING A chemical bond is a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together. Types of Bonds: Ionic bond- the transfer of electrons of cations (metals) and anions (nonmetals). In purely ionic bonds, atoms completely give up electrons to other atoms. Has an electronegativity between 1.7 and 3.3 Covalent bond- is a chemical bond that forms when atoms share one or more pairs of electrons. Usually sharing of electrons occurs when a nonmetal binds with a nonmetal.

C OVALENT BONDS Nonpolar covalent bond- covalent bond in which electrons are shared equally and therefore there is a balanced electrical charge a) -has an electronegativity of 0 to 0.3 b) -shares electrons equally ex. Br to Cl c) -occurs when two atoms of the same element bond (H 2 ) Polar covalent bond- - covalent bond in which the atoms have an unequal attraction for the shared electrons a) has an electronegativity of 0.3 to 1.7 b) unequal attraction of shared electrons ex. H to S

C HEMICAL BONDING The type of bond formed is determined by the difference in the electronegativities of the atoms involved. 0.0 Non-polar Covalent 0.3 Polar Covalent 1.7 Ionic 3.3 Example: Fluorine (EN=4.0) bonds with Cesium (EN= 0.7) Difference in electronegativities: =3.3 This bond would be an ionic bond. Fluorine is very electronegative and gains electrons from cesium causing cesium to become an anion.

C OVALENT AND M OLECULAR C OMPOUNDS Molecule- a neutral group of atoms held together by a covalent bond ex. H 2 O and sugar(C 6 H 12 O 6 ) Molecular compound- simplest units are molecules ex. O 2 Chemical formula- is a way of writing a combination of two elements in their simplest form to represent the number of atoms each contain Diatomic molecule- molecule that only contains 2 atoms ex. I 2, O 2, Cl 2, H 2, F 2, Br 2, N 2, S 2

F ORMATION AND C HARACTERISTICS OF C OVALENT B ONDS Covalent bonds form at the lowest potential energy rates ex. H to H Electrons become attracted at the same time the nuclei of the two atoms are repelled, this force of attraction continues until the attraction force out numbers the repulsive force Bond energy is the force required to break the bond; covalent bonds are easier to break than ionic bonds

O CTET R ULE The noble gases are stable and inert gases who’s outer electrons (valence) are full with 8 electrons. This is a combination of the s block and the p block of the period. All elements want to mimic the octet rule by combining with other elements or being a charged ion ex. H 2 or Na + Most main group elements form covalent bonds (Groups 1,2 & 13-17) Exceptions to the rule fall in the boron family, because it has 3 valence electrons

E LECTRON -D OT N OTATION & L EWIS S TRUCTURES Electron-dot notation represents the valence electrons of an atom, which is 1 to 8 The rule is in filling : right, left, top, bottom and then all over again until each side has two electrons Lone pair of unshared electrons are valence electrons which do not bond Lewis structures are the combinations of the electron-dot notations of elements when they combine to show the types of bonds which can occur Structural formula- represents the bonding of two or more atoms in the form of a dash ex. F-F or H-Cl

E LECTRON -D OT N OTATION & L EWIS S TRUCTURES Single Bond- one pair of electrons being shared ex. H-H Double Bond- two pairs of electrons being shared ex. C=0 Triple Bond- three pairs of electrons being shared ex. N=N Multiple Bonds- represent a combination of more than 1 type of bond ex. H-C=C-H Resonance – shows that there is more than one type of possible bonding combination and therefore, you have to show all types ex. O=O-O or O-O=O