Chapter 5.2

Molecular Substances

• Most solid compounds at room temperature are ionic.

• Most liquid and gas compounds at room temperature are covalent.

• There are exceptions to these rules.

• Exceptions: solid covalent cpds.»Sugar»Moth balls»Sand»Butter

• Covalent compounds/molecules are much more variable than ionic cpds.

• Differences due to fact that covalent bonds are weaker than ionic bonds.

• Covalent compounds react very differently due to different bond strengths.

• Ex: diamonds- hard, carbons tightly bound to each other

crayons and wax- soft and have low melting point due to weak bonds

Separation of SubstancesDistillation:Method of separating substances in a mixture byevaporation of the liquid and condensation of its vapor

Molecular ElementsI. Molecular Element:

molecule with two or more of the same element

- Diatomic elements: 2 of same elements in a cpd.» 7 found naturally in diatomic state

H2 gas at RT H : HN2 “ “ N ::: NO2 “ “ O :: OF2 “ “ F : FCl2 “ “ Cl : ClI2 solid at RT I : IBr2 liquid at RT Br : Br

WHY ARE THESE NOT FOUND AS MONOATOMIC ELEMENTS?

II. Allotropes:forms of elements that differ in the way the atoms are bonded

- have different structures of the same element

- properties of allotropes differ from the single element and from other allotropes

AllotropesA. Oxygen Allotropes

O2 (diatomic) O=O

Ozone (O3)

O2 + O O3

- formed by:»O2 + uv light or lightning»O2 + pollution (smog)» layer in upper atmosphere, filters out

harmful UV light

Allotropes

B. Carbon Allotropes

- most versatile element in forming different structures of covalent bonds (4 valence electrons)

- can make more covalent bond formations than any other element Eight allotropes of carbon:

a) Diamond b) Graphite c) Lonsdaleite d) Buckyball C60e) C540, f) C70g) Amorphous carbonh) Single-walled carbon nanotube

C. Phosphorous Allotropes

- white: ignites in air, flares

- black: semiconductors

- red: match sticks

* differences result from temperature and pressure during formation

Formulas and Names of Molecular Compounds

Types Molecular Compounds

1. Inorganic: no carbon

ex: HCl, NO2, H2O, SO4

2. Organic: contain carbon

ex: CO2, C2H6O3, CH4, CCl4

Naming Inorganic CompoundsRules

1. Write name of first non metal

2. Write name of second non metal and change ending to “ide”

- first element should be further left on periodic table (except H)

- if both in same group, first element should be closer to bottom of periodic table

3. Add a prefix to each element to tell how many atoms of each element are present

- if first element has only 1 atom, not necessary to write “mono”

4. If using prefix “mono” and o-o or o-a are next to each other, drop the first “o” or “a”

ex: monooxide monoxide pentaoxide pentoxide

Write the names of the following molecules:

BF3

PBr5

C5H9

IF7

N2O6

SiO2

H2S

N8O4

CS2

P4O10

Write the formulas for the following molecules:

Carbon tetrachloride

Sulfur trioxide

Dinitrogen pentoxide

Carbon monoxide

Nitrogen monoflouride

Phosphorous pentachloride

Disulfur hexaselenide

Tricarbon heptabromide

Hydrogen monochloride

Octasulfur diastatide

Formal vs Common NamesFormal Name

tells chemical composition of compoundex: CCl4 carbon tetrachloride

NaCl sodium chlorideH2O dinitrogen monoxide

Common Name“nickname”, easier to say, does not tell composition

ex: NaCl saltH2O waterHCl hydrochloric acidH2SO4 sulfuric acidHNO3 nitric acidNH3 ammonia

Organic Compounds• Contains carbon• Names based on hydrocarbon bonds (H-C)

– Hydrocarbon: organic compound that contains only hydrogen and carbon atoms

»Found in fossil fuels (gas, petroleum)»Form long chains as compounds

Ex: CH4 methane C3H8propane

C4H10butane

C8H18octane

Study for the test !