EXPERIMENT 4 Properties of Ionic and Molecular Covalent Compounds

THE PERIODIC TABLE OF ELEMENTS Non - metals Metals Metalloids Non - metals

Ionic bond: A chemical bond resulting from the electrostatic attraction of an anion (negatively charged ions) and a cation (positively charged ions). Ionic compounds : Formed when metals and non – metals react, contain ionic bonds, solid at room temp, Do not exist as discrete molecules, anions and cations are arranged in three dimensional geometrical pattern. Examples : NaBr, LiBr, K 2 O, NiS, FeCl 2 We classify chemical bonds as ionic, polar covalent, and nonpolar covalent based on the difference in electronegativity between the bonded atoms. (Note: The easiest way to identify an IONIC bond is if the compound contains a METAL.) TYPES OF COMPOUNDS 1. IONIC COMPOUNDS :

Ionic Representation in NaCl Crystal : Negatively charged chlorides are attracted to positively charged sodium ions. Like charges repel!!! Geometrical Square array of NaCl structure Each Na + is surrounded by six Cl - ions and vice versa! Bonding in the structure CANNOT be classified as intra- or inter, only ionic bonding exists. Ionic bonding strength in NaCl is similar to covalent bonding in NO.

Covalent bond: A chemical bond resulting from two atoms sharing one or more pairs of electrons. Covalent compounds : Formed by the reaction of non - metals with non – metals. Categories of Covalent compounds : A.Molecular Covalent Compounds : Exist as discrete molecules (liquids,solids or gases) Examples : NO, H 2 O, SO 3, CH 4 TYPES OF COMPOUNDS……..continued 2. COVALENT COMPOUNDS : Intramolecular forces – Covalent bonding, and Intermolecular forces – Weak Van Der Waals forces

B.Network Covalent Compounds : No discrete molecules. Atoms are networked by covalent bonds! Eg. SiC and SiO 2.

PROPERTIES OF IONIC AND MOLECULAR COVALENT COMPOUNDS

TYPES OF COMPOUNDS……..continued ALLOY: 3. ALLOY: ALLOY - ALLOY - is a mixture of metals bonded by metallic bonding character Brass is a metal alloy made of coper and zinc Stainless Steel is a metal alloy of iron, chromium, and trace amounts of carbon and nickel Bronze is a metal alloy made of copper, tin and aluminum BRASSSTAINLESS STEELBRONZE

MELTING POINT OF COVALENT AND IONIC COMPOUNDS MELTING POINT - the temperature at which a substance changes from the solid state into the liquid state without change in temperature. If temperature is removed, some liquid will freeze without change in temperature this Is its FREEZING POINT. Intensive properties are independent of the amount of material being tested (example = density, melting point, boiling point) Intramolecular forces are very strong. When a compound goes from one phase to another (liquid to vapor, solid to liquid, etc.) intermolecular forces are being broken (i.e. dipole moment, hydrogen bonding, van der Waals). During melting, the heat energy (kinetic energy) breaks the rigid structure in the solid. Intermolecular forces are much weaker than the ionic force of attraction or covalent bonds. That is why covalent compounds require less energy to melt than ionic compounds. Acetic acid (Organic Covalent) melts at 16 0 C, NaCl (inorganic ionic) melts at C.

Acetic acid – HC 2 H 3 O 2 (Organic Covalent) melts at 16 0 C, potassium acetate KC 2 H 3 O 2 - (inorganic ionic) melts at between C. Supercooling – where a liquid cools momentariry below its freezing point without freezing. A liquid will freeze without change in temp 0 at its FREEZING POINT

QUALITATIVE DETERMINATION OF MELTING POINT and FREEZING POINT Only melting point RANGES will be determined in the experiment, NOT exact accurate values! No thermometers will be used as many would be needed to read temperatures of 0 – C

ELECTRICAL CONDUCTIVITY AND ELECTROLYTES Electrical Current – transfer of electrons (moving electrical charge). Bulb glows if the liquid into which electrodes are dipped into conduct current. A liquid will be a good conductor of electricity if it has ions in it (cations or anions) The more the ions, the more the conductivity, the brighter the bulb in the circuit lights