Molecular Compounds

Types of Compounds

Ionic

• Metal (or NH4+) with a

non-metal• Transfer of electrons from

metal non-metal• Have ionic bonds

Molecular

• Non-metals only• Sharing of electrons

between non-metals• Have covalent bonds

Properties

Ionic

• Solid (s)• High melting points• When dissolved in water,

aqueous (aq), ionic compounds are electrolytes (good conductors of electricity)

• Electrolytes when melted.

Molecular

• Solid (s), liquid (l) or gas(g)

• Lower melting points• When dissolved in water,

(aq) or melted they are not electolytes

A molecular compound

• A molecular compound, is a pure substance that is formed from covalent bonds between nonmetals.

• Examples include:

• Water H2O (l)

• Carbon Dioxide CO2 (g)

• Oxygen O2(g)

Covalent Bonding• A covalent bond is a form of chemical bonding that is

characterized by the sharing sharing of pairs of electrons between atoms. This sharing allows the atoms to form a stable electron arrangement.

• For H2(g) that stable arrangement has 2 e-’s• For other molecular compounds an octet is required by

sharing.

Diatomic Molecules• A diatomic molecule is a

molecule consisting of only two atoms, of either the same or different chemical elements.

• http://www.dnatube.com/video/1290/Covalent-bond

O2 Oxygen

N2 Nitrogen gas

Diatomic Molecules

Here are some examples of diatomic molecules (same element):

hydrogen (H2)nitrogen (N2)oxygen (O2)fluorine (F2)chlorine (Cl2)bromine (Br2)iodine (I2)

Here are some examples of diatomic molecules (different elements):

CO – Carbon MonoxideCO – Carbon Monoxide

NO – Nitrogen NO – Nitrogen MonoxideMonoxide

HF – Hydrogen HF – Hydrogen FluorideFluoride

HCl – Hydrogen HCl – Hydrogen ChlorideChloride

HBrHBr – – Hydrogen BromideHydrogen Bromide

NN22O- dinitrogen O- dinitrogen monoxidemonoxide

SOSO33- sulfur trioxide- sulfur trioxide

Diatomic Elements

• I Bring Clay For Our New Home

• *to help you remember the molecular diatomic elements.

Diatomic Compounds• Since many combinations of some atoms are

possible, the number of atoms in the molecule is often stated using Latin prefixes.

– Carbon monoxide is CO while carbon dioxide is CO2.

– Memorize the prefixes!

Common Prefixesone mono   six hexa

two di   seven hepta

three tri   eight octa

four tetra   nine nona

five penta   ten deca

• NBr3 = Nitrogen tribromide

• Dihydrogen dioxide = H2O2

Rules

• Use the Greek prefixes to indicate how many of each element are present in the formula. Mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca,…

• Drop mono for the first element.• Drop all prefixes if the first element is hydrogen.• Drop the second o in mono prior to a vowel.• Drop the a in prefixes ending in a prior to a vowel.

Examples:

• N2S

• N2O3

• CO2(g)

• HCl• CO(g)

• N2O4

• Dinitrogen monosulfide• dinitrogen trioxide • carbon dioxide• hydrogen chloride• carbon monoxide• dinitrogen tetroxide

Naming Molecular Compounds

• Can be more complicated than ionic compounds.

• There are also “common” names that will need to be memorized, such as:

• Water (H2O)• Methane (CH4)• Hydrogen peroxide (H202)• Sucrose C12H22O11

• Page 204– #1 5

Writing Formulas for Molecular Compounds

• Method is similar to the one used for ionic compounds.

• The combining capacity of a nonmetal tells you how many covalent bonds are needed to form a stable molecule.

• To figure out an atoms combining capacity you need to see where it falls on the periodic table or know how many valence electrons it has.

Methane

CH4

Writing Molecular Compounds Step by Step

Carbon & Sulfur

• Step 1:– Write the symbols and combining capacities

• Step 2:– Use the crisscross rule & the combining

capacities to get the proper subscripts.

Writing Molecular Compounds Step by Step

Carbon & Sulfur

This formula becomes C2S4 reduced to CS2.