Chapter 7  Chemical Bonds

Chemical bond  Link between atoms that results from attractions of their nuclei for e -

1. Ionic bond  Attraction between (+) and (-) ions, exchange of e -  Usually between metals and nonmetals

Ion  Atom or group of atoms with a (+) or (-) charge  Cation: (+) chg  Anion: (-) chg

e.g. sodium

e.g. chlorine

Na and Cl ions  ionic bond

Polyatomic ions  Charged group of bonded atoms  e.g. phosphate ion (PO 4 3- )

2. Covalent bonds  Sharing of e -  Usually between nonmetals nonmetals

Covalent bonding  Molecule- smallest unit quantity of matter that can exist by itself, e.g. atom of He, O 2, H 2 O  Diatomic molecule-2 atoms, e.g. HCl, H 2

e.g. hydrogen molecule

Bond types

 Chemical bonds are usually not completely ionic or covalent ionic Polar covalent Non polar covalent Difference in electronegativity

electronegativity  Measure of ability of an atom in a chem. cmpd. to attract electrons

Chemical formula  Type and relative # of atoms in a chemical compound, e.g. H 2 O

e - config. and bonding

Octet rule  Atoms often gain, lose, or share electrons to achieve the same number of electrons as the noble gas closest to them in the periodic table  Because all noble gasses (except He) have filled s and p valence orbitals (8 electrons), many atoms undergoing reactions also end up with 8 valence electrons.  Octet Rule: Atoms tend to lose, gain, or share electrons until they are surrounded by 8 valence electrons  Note: there are exceptions to the octet rule, e.g.He

Valence electrons  Electrons lost, gained, or shared in formation of chemical cmpds.

Lewis structures  N 2 (nitrogen)  Carbon tetrachloride

 Lewis structure  Structural formula

Structural formula  Indicates the kind, number, arrangement, and bonds of atoms in molecules

Single bonds  Sharing (1) pr. of e -

Double bond  Sharing (2) pr. of e -

Triple bond  Sharing (3) pr of e -

3. Metallic bonds  Metal-metal bonds, electron ‘sea’

Metallic bonding  Results from attraction between (+) ions and surrounding mobile electrons (electron sea)  Motion of free electrons accounts for high conductivity of heat and electricity  Malleability and ducticity possible because bonding is not directional

4. Hydrogen bonds  Weak bonds between molecules due to partial charges on atoms  e.g. water

Polarity of water molecule  hydrogen bonding

Review: ionic or covalent?  Ca and Cl  Ionic  Na and F  Ionic  N and O  Covalent  H and H  Covalent

Review: Lewis Structure 1.H + H + O 2.C 2 H 4 (ethene)

What kind of bonds?

Define:  Covalent bond  Ionic bond  Metallic bond  Hydrogen bond  Diatomic molecule  Cation  Anion  Electronegativity