Types of substances Phase at room temperature Melting point ConductivitySolubility in water MetallicSolid Except Hg Very highGood (high) in solid and liquid phases No (insoluble) IonicSolid onlyHighGood (high) in liquid and aqueous phases Yes (soluble) MolecularSolid, liquid, gas LowPoor (low) in all phases Yes (slightly soluble) Network solid Solid onlyExtremely high Very poor in all phases No (insoluble)

Examples of Four Types of Substances and their melting points Type of substanceExampleMelting Point Molecular Solid Ice (H 2 O)O°C Ionic Substance Salt (NaCl)801°C Metallic Substance Gold (Au)1065°C Network Solid Diamond (C)3550°C

Metallic substances are metallic elements Contain atoms held together by metallic bonding Normally exist as solids at room temperature Mercury is the only liquid metallic element ExamplesCaNi High melting points (highly stable) Hard solid Insoluble in water High (good) electrical conductivity as solids and liquids (conductivity is due to mobile valence electrons)

Ionic substances are compounds formed by positive and negative ions. Positive ion is usually a metallic element. Negative ion is usually a nonmetal element or a polyatomic ion. Binary ionic compounds containing only ionic bonds formulas usually contain a metal and a nonmetal NaCl (sodium chloride)Al 2 O 3 (aluminum oxide) Ionic compounds containing both ionic and covalent bonds (usually contain three or more elements) formulas usually have a polyatomic ion MgSO 4 magnesium sulfateNH 4 Cl ammonium chloride Properties High melting points (stable, require high heat to decompose) High or good electrical conductivity (only as liquids and aqueous Hard solids Very soluble in water

Molecular (covalent) substances are substances that contain molecules (smallest units of molecular substances; usually a group of nonmetal atoms covalently bonded) All three phases: solid, liquid, gas Polar or nonpolar depending on the charge distribution in the molecule Low melting points Low (poor) electrical conductivity Solids are usually soft and brittle Slightly soluble in water Examples H 2 O water Neneon CO 2 carbon dioxide H 2 hydrogen

To determine formula or name of a substance from properties given in a question DETERMINE if properties described are metallic, ionic, or molecular CHOOSE a formula that represents that type of substance you determined To determine correct set of properties of a name or formula of a substance DETERMINE if the formula is of metallic, ionic, or molecular solid CHOOSE properties which belong to the type of substance you had determined

Molecular substance can be classified as nonpolar or polar based on the symmetry of its molecules Nonpolar substances contain symmetrical nonpolar molecules Polar covalent bonds between atoms that are symmetrically arranged H – HF F - C - F F Polar substances contain asymmetrical polar molecules Polar covalently bonded atoms that are asymmetrically arranged H – FO H

Nonpolar substances contain molecules that have symmetrical structure (charges are evenly distributed – there are no positive or negative poles (nonpolar)). Nonpolar molecules can be formed by polar and nonpolar covalently bonded atoms. Nonpolar molecules containing nonpolar covalent bonds (electrons are shared equally; structures are symmetrical and linear) H – HCl – Cl N = N H 2 Cl 2 N 2

Nonpolar molecules containing polar covalent bonds (electrons are shared unequally; one atom has a + charge and the other has a – charge; atoms are symmetrically arranged H Cl H - C - HO=C=OCl – C – Cl H Cl Nonpolar monatomic elements – all group 18 Noble gases belong to this category of nonpolar molecules Ne (neon)Ar (argon)

Polar substances contain molecules that have asymmetical structure (charges are unevenly distributed within the molecule). Uneven charge distribution makes one atom positive and the other atom negative. Polar means two poles + and -. Polar (dipole) molecules can only be formed by polar covalently bonded atoms. HClH – Cl H 2 O O H NH 3 H – N – H H

In a polar molecule because of uneven electron sharing, one atom appears to be more negative and the other appears to be more positive To determine the negative atom – CHOOSE the higher electronegativity atom To determine the positive atom – CHOOSE the lower electronegativity atom

Structure and shape of a molecular substance are very important because they determine properties of the substance Molecular shapes LinearO=OO 2 oxygen Tetrahedral H H – C – HCH 4 methane H Bent OH 2 O water H H

Trigonal planar Cl AlCl 3 aluminum trichloride Al Cl Cl Trigonal pyramidalH – N – H NH 3 ammonia H

ConceptsExplanations Depends onTypesDescriptionExamples Bond polarityDescribes polarity of a covalent bond between two atoms Depends on the type of bonds or their electronegativity difference Polar bond Nonpolar bond Bond that produces + and – ends on bonded atoms Found between two different nonmetals Does not produce + and – ends Found between two of the same nonmetals C – H P – Cl H – H O=O Molecular polarityDescribes the overall polarity of a molecule Depends on the symmetry and charge distributions on a molecule Polar molecule Nonpolar molecule Asymmetrical structure Uneven + and – charge distributions Symmetrical structure Even + and – charge distributions H – F O H H Cl – Cl H H C H H

Molecular symmetry Describes the overall arrangement of atoms to make a molecule Depends on the nature or type of atoms and the number of each atom of the molecule Symmetrical molecules Asymmetrical molecules Arrangement of atoms is evenly distributed Arrangement of atoms is unevenly distributed Br – Br H H C H H H – Cl H – N – H H Molecular shapes Describe structural shapes of molecules due to arrangements of its atoms Depends on several factors including types of and number of atoms, as well as shared and unshared electrons Linear Tetrahedral Bent Pyramidal H – Cl 0=C=O Cl Cl – C – Cl Cl S H H H – N – H H

Bond polarity refers to how ionic, polar, or covalent is a bond between two atoms Molecular polarity refers to how polar a molecule of a substance is A compound may contain a bond that has more ionic or more covalent characteristics than a bond between atoms of another compound. Some molecules also have more polar characteristics than others do. The degree of bond and molecular polarity of substances depends on the electronegativity difference between the two atoms in the formula of the substance.

To calculate electronegativity difference between two atoms in a bond: Electronegativity difference = high electronegativity – low electronegativity To determine which formula is most or least ionic or polar Electronegativity difference scale ranging from 0 – As electronegativity difference increases Least polar Most polar Least ionic Polarity and Ionic characteristics increase Most Ionic Most covalentCovalent characteristic decreases___________ Least covalent The smaller the difference in electronegativity, the more covalent, the less ionic and the less polar the substance. The larger the difference in electronegativity, the less covalent, the more ionic, and the more polar the substance.

To determine Most ionic, most polar, or least covalent LOOK for highest electronegativity difference Least ionic, least polar, or most covalent LOOK for lowest electronegativity difference LiClCl = 3.2least ionic Li = 1.0least polar 2.2most covalent KClCl = 3.2 K = FrClCl = 3.2most ionic Fr = 0.7most polar 2.5least covalent