COVALENT BONDING

COVALENT BONDS Covalent bonds = Sharing electrons Octet rule: Atoms still need to become stable by having 8 electrons in their outer energy level!! Instead of losing or gaining valence electrons, atoms in covalent bonds share valence electrons These bonds take place between nonmetals and nonmetals

COVALENT BONDS Atoms that combine through covalent bonds (electron sharing) form molecules Example: Nonmetal

COVALENT BONDS Compound Properties Have lower melting and boiling points than ionic compounds - No bonds to be broken as in ionic compounds - Molecules are very close to each other, but not bonded Are soft and “squishy,” compared to ionic compounds - Molecules move very easily around each other because there are no bonds between them - These makes them flexible and not hard http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom1s2_11.swf

COVALENT BONDS Compound Properties They are more flammable than ionic compounds - Most covalent compounds have carbon and hydrogen which burn very easily with oxygen - Those without carbon and hydrogen do not burn They do not conduct electricity in water - Ion (charge carriers) movement in water is the conduction of electricity - Covalent compounds do not have ions They are usually not very soluble in water - “Like dissolves like” rule - Compounds dissolve in compounds with similar properties - Water is polar solvent and most covalent compounds are nonpolar = then do not dissolve in water

Single covalent bonds Made up of two shared electrons Usually, one of the shared electrons comes from one of the atoms in the bond and the other electron from the other atom in the bond Halogen (Group 7A) elements exist as molecules of single covalent bonds (more stable) Example: Hydrogen molecule (H ) 2

Single covalent bonds Hydrogen Molecule . . . . H H H H + Each hydrogen atom has 1 valence electron Bonding pair Another way to represent the hydrogen covalent bond: H H http://web.jjay.cuny.edu/~acarpi/NSC/5-bonds.htm Bonding pair

Single covalent bonds Water Molecule . . . . . . . . . . . . . H H . O + + H O . . H OR . . . . H O H http://web.jjay.cuny.edu/~acarpi/NSC/5-bonds.htm

Multiple Covalent Bonds Covalent bonds can have more than one pair of shared electrons Atoms of the elements carbon, nitrogen, oxygen, and sulfur very often form multiple covalent bonds Multiple bonds can be double or triple covalent bonds

Double covalent bonds Oxygen Molecule . . . . . . . . . . . . . . . . O . O . . O . + O Each oxygen atom has 6 valence electrons Bonding pairs

Triple covalent bonds Nitrogen Molecule . . . . . . . . . . . . N . N . N N + Each nitrogen atom has 5 valence electrons Bonding pairs http://www.tutorvista.com/content/chemistry/chemistry-i/chemical-bonding/covalent-bond-animation.php

How do elements combine?

Naming Covalent Compounds Names are usually composed of two words - First is the name of the first element in the formula - Second is the name of the second element in the formula, but changing the ending to –Ide Example: HF = hydrogen fluoride

Naming Covalent Compounds If there is more than one atom of an element in the molecule, then we need to use prefixes to tell us how many are there 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 Covalent Compounds Some common names to some very important covalent compounds Formula Common Name Molecular Compound Name H O water dihydrogen monoxide NH ammonia nitrogen trihydride N O nitrous oxide (laughing gas) dinitrogen monoxide NO nitric oxide nitrogen monoxide CH methane carbon tetrahydride 2 3 2 4

Naming Covalent Compounds Examples…… P O = diphosphorus pentaoxide CO = carbon monoxide CF = carbon tetrafluoride 2 5 4