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 Substances Distillation: Method of separating substances in a mixture by evaporation of the liquid and condensation of its vapor

Molecular Elements I. 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 : H N2 “ “ N ::: N O2 “ “ O :: O F2 “ “ F : F Cl2 “ “ Cl : Cl I2 solid at RT I : I Br2 liquid at RT Br : Br WHY ARE THESE NOT FOUND AS MONOATOMIC ELEMENTS?

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

Allotropes A. Oxygen Allotropes O2 (diatomic) O=O Ozone (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 C60 e) C540, f) C70 g) Amorphous carbon h) Single-walled carbon nanotube

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 Inorganic: no carbon ex: HCl, NO2, H2O, SO4 2. Organic: contain carbon ex: CO2, C2H6O3, CH4, CCl4

Naming Inorganic Compounds Rules 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 Names Formal Name tells chemical composition of compound ex: CCl4 carbon tetrachloride NaCl sodium chloride H2O dinitrogen monoxide Common Name “nickname”, easier to say, does not tell composition ex: NaCl salt H2O water HCl hydrochloric acid H2SO4 sulfuric acid HNO3 nitric acid NH3 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 C3H8 propane C4H10 butane C8H18 octane

Study for the test !