Molecular Compounds

Molecular Compound• atoms of non-metals combine and form a pure

substance• example: nitrous oxide (N2O)

• the atoms are joined by covalent bonds• each bond shares a pair of electrons• bonded atoms form a MOLECULE

Covalent Bonds• connection where two atoms share a pair of

electrons• the electron pair belongs to both atoms• attraction of atoms holds them together

SMART Board Activity

Remembering Non-Metals

• non-metal valence shells are almost full• the spaces can attract other electrons• allows non-metals to get close to each other• the two nuclei form strong attractions for each

other’s electrons• but not strong enough• net effect – share the electrons

Molecular Elements• molecular elements are two or more atoms of the same

element• a molecule made of only two atoms is called a diatomic

molecule

Molecular Elements that Commonly Form Diatomic Molecules:

Element Formula

bromine Br2

chlorine Cl2

fluorine F2

hydrogen H2

iodine I2

nitrogen N2

oxygen O2

Other Diatomic Molecules• there can be other types of diatomic

molecules• some can share 2 pairs of electrons• e.g. O2

• other diatomic molecules can be made of two different elements

• e.g. hydrogen and fluoride HF

Properties of Molecular Compounds

• at room temperature they can be liquid, solid or gas

• generally soft solids• if dissolved in water, they do not conduct

electricity• have relatively low melting points• two non-metallic elements can combine in

different ways and form different compounds• e.g. hydrogen and oxygen:water = H2O hydrogen peroxide = H2O2

Naming Molecular Compounds• any molecular compound that contains two

elements and does not contain hydrogen uses Greek prefixes

• the prefix indicates how many atoms of each element are in the compound

• e.g. P2O5 is diphosphorus pentoxide

• di- means 2, pent- means 5

Number of Atoms Prefix1 mono-2 di-3 tri-4 tetra-5 penta-6 hexa-7 hepta-8 octa-9 nona-

10 deca-

Naming Rules1. Name the first element (e.g. nitrogen)2. Name the second element, using the suffix “-ide”

(e.g. oxide)3. add prefixes to indicate the number of each atom

(e.g. dinitrogen monoxide)

Note: mono is not used in first element; if it is required before oxide, the last “o” in prefix is dropped

e.g. N2O

Hydrogen

• hydrogen is unique• often does not follow same naming• has given names:

Name Formulawater H2O

hydrogen peroxide H2O2

ammonia NH3

methane CH4

hydrogen sulfide H2S