SCH3U Chemical Bonding Ionic vs. Covalent Compounds Ms. Yusuf

Formation of Bonds Chemical Bonds are formed between two atoms using shared valence electrons; this is the force that holds atoms together in compounds. Valence Electrons are the electrons that occupies the outermost energy level of an atom

Type of Bonds Ionic vs. Covalent Ionic bonding occurs between metals and non-metals Covalent bonding occurs between non-metals Note: Bonding between metals is called Metallic bonding Video Clip: Chemical Bonding

Octet Rule Most Noble gasses have 8 electrons in their outer shell. This is a stable conformation. Thus, the noble gasses do not react with other elements. In other words, noble gasses are very stable.

Octet Rule (Continued) When atoms form ions or combine in compounds they obtain electron configurations of the nearest noble gas (eight electrons in their valence shells)

Ionic Bonding Ionic Bonds are formed from the electrostatic attraction of positive and negative ions An atom that can lose an electron to become a positively charged ion, called a cation An atom can gain electrons to become a negatively charged ion, called an anion In each case, the atom attains a noble gas configuration with its valence electrons. A noble gas configuration is defined as a completely filled outer shell, like the noble gases.

Ionic Bond: Example (Na and Cl)

Ionic Bond: Example (Al and O) Al O O O

Examples of Ionic Bonding using Lewis Structures Magnesium and Fluorine Calcium and Oxygen Potassium and Sulfur

Covalent Bonding Covalent bonding occurs between two non-metals. Covalent bonding is different from ionic bonding because electrons are shared instead of transferred. Each atom has eight shared electrons

Covalent Bonding: Example (H and F) H FHF

Covalent Bonding Using Lewis Structures Silicon Oxygen Hydrogen and chlorine Bromine and Bromine

Elements will not share the electrons in a bond equally The electronegativity (EN) of an element determines its ability to attract electrons in a bond When elements are bonded together, the more electronegative element attracts the electrons Example: HF Flourine is more electronegative. The electrons in the bond are attracted towards the fluorine atom Polar Bond (Dipole Moment) EN H = 2.1 EN F = 4.0 ∆EN H-F = = 1.9

(Continued) This is not a complete transfer of an electron from hydrogen to fluorine; it is merely a drifting of electrons toward fluorine When a charge separation of this type is present, the molecule possesses an electric dipole, so called “dipole moment” and the bond is called a POLAR COVALENT BOND H : FCl : Polar Covalent Covalent

Polar Covalent Compound 0.5 < Electronegativity difference < 1.7 This difference is great enough for the bonding electron pair to spend more time near the more electronegative atom than the less electronegative atom.

(Continued) Example: Water (H 2 O) ∆EN = 1.24 (which is between 0.5 and 1.7) Polar Covalent Bond Oxygen = a slightly negative charge Hydrogen = a slightly positive charge Since the hydrogen does not completely transfer its electron to the oxygen, the their respective charges are indicated as  + (the indication of partial positive charge) and  - (indication of partial Negative charge). O HH  + --

∆EN 3.3 Comparison of Ionic, Non- polar covalent and Polar covalent bonding [Na] + [Cl] - H  + - Cl  - Cl - Cl

Summary Chemical Bonds are formed between the atoms in molecules The bonds are formed from the valence electrons of the atoms and the resulting bond allows each atom to achieve a noble gas configuration (the most stable arrangement of electrons around the atom: Octet Rule) The types of bonding can be classified as: 1. Covalent (non-metal bondin; 0<∆EN<0.5) 2. Polar covalent bonds (non-metal bonding with a dipole moment; 0.5<∆EN<1.7) 3. Ionic (metals + non-metals; 1.7 <∆EN< 3.3)

Questions Complete the chart: Identify each compounds as ionic or covalent: CCl 4,HCI, MgF 2, H 2 O,NH 3, NaCl, OH, H 2 Show how the bond forms between Li+Cl, Mg +O (Follow the Octet Rule) as well as Li + O