 A covalent bond is formed when two or more nuclei share electrons in order to achieve a stable electron configuration (noble gas).  Covalent bonds often occur between two non- metals of the same element. (Diatomics)  H,O,F,Br,I,N,Cl  Atoms of different elements can also combine to form a covalent bond.  Example: water, carbon dioxide

 There are different types of covalent bonds. They are:  Non-polar Covalent  Polar Covalent  Multiple Covalent  Double bonds  Triple bonds

 A nonpolar covalent bond exists when there is an equal sharing of electrons between two nuclei.  Nonpolar covalent bonds are formed between atoms having equal or close electronegativity values.  The diatomics always make nonpolar covalent bonds because they are non-metals and their electronegativity values cancel.  If the electronegativity different is between 0 and 0.4 the compound is considered nonpolar covalent.

 Atoms involved in a polar covalent bond have an unequal sharing of electrons.  This can be determined based on their differences in electronegativity.  The element with the higher electronegativity value attracts the shared electrons more strongly.  This causes a portion of the molecule to acquire a partially negative charge.  The other end of the polar molecule acquires a partially positive charge.

 H-Cl and H-I are two common polar compounds.  Hydrogen obtains a partially positive charge and the halogens obtain a more negative charge.  This happens because the halogens (group 17) have a higher electronegativity value than hydrogen.

 Water is a polar covalent compound.  In a water molecule, the oxygen atom takes on the negative charge and the hydrogens take on the positive charge.

 Atoms in covalent bond may share more than one pair of electrons.  This additional sharing of electrons results in the formation of a multiple covalent bond.  Double bond- the sharing of two pairs of valence electrons.  Triple bond- the sharing of three pairs of valence electrons.

 Every Hydrogen atom has one line connecting it to other atoms or itself. (single bond)  Every Oxygen atom has two lines connecting it to other atoms or itself. (double bond)  Every Nitrogen atom has three lines connecting it to other atoms or itself. (triple bond)  Every Carbon atom has four lines connecting it to other atoms. (not itself because Carbon is not diatomic) – (single bonds)

HH(single) O O(double) NN(triple) ClCl(single)

 A molecule is the smallest discrete particle of an element or compound formed by a covalent bond.  Each atom in a molecule obtains an electron configuration of a noble gas.  Molecular substance can either be solid, liquid, or a gas.  The state of matter depends on the strength of the forces of attraction.  Molecules tend to be soft, poor conductors of heat and electricity, and they have low melting and boiling points.

 A large majority of all chemical compounds on Earth are covalent (either polar or non-polar).  A vast majority of covalent compounds are organic, meaning they contain carbon and hydrogen.  Plastics, foods, living things, oil, etc. are all organic compounds.  There are thousand of these compounds and we use them everyday.

 If a molecule contains polar bonds does not mean that the compound itself is polar.  For example, the Hydrogen – Carbon bond is polar but the compound CH4 is a non-polar compound.  To understand this, one must look at the molecules shape.  Asymmetrical molecules are polar  Symmetrical molecules are non-polar because the pull of the various polar bonds offset each other.

 Polyatomic ions are two or more different atoms bonded together that act as one unit.  Polyatomic ions must also contain an ionic bond to be considered stable.  The bonds that hold the polyatomic ion together are covalent.  A polyatomic ion plus a metal will contain both ionic and covalent bonds.

 Ionic, metallic, and covalent bonds all have different properties.  This table explains the main difference between all three BondMelting/BoilingHardnessConductivity SLAq. MetallicHighHardYes CovalentLowSoftNo IonicHighHardNoYes

 Molecules have attractive forces acting on them in the solid, liquid and gaseous state.  These forces are:  Ionic forces  Dipole forces  Hydrogen bonding  Induced dipole