Covalent Bonding Covalent Bonding 9 1 The Covalent

Covalent Bonding

Covalent Bonding • 9. 1 The Covalent Bond • A covalent bond usually takes place between two non-metal elements • Covalent bonds generally occur between elements that are close together on the periodic table.

Covalent Bonding • Octet Rule- When two atoms both need to gain valence electrons to complete the octet rule, they share electrons in order to gain the configuration of a noble gas : 8 valence electrons.

Covalent Bonding • A covalent bond is a chemical bond that results from the sharing of valance electrons.

• Covalent Bond- the shared electrons in a covalent bond are considered to be part of the complete outer level for both atoms involved.

Molecule A Molecule- is formed when two or more atoms bond covalently. A compound that is formed by molecules is called a molecular compound.

Formation of a covalent bond A valence orbital containing an electron from one atom overlaps a valence orbital from another atom. Because the nuclei of both atoms have a positive charge, they are attracted to the shared concentration between them.

Diatomic molecules (Mr. Br. INCl. HOF) • Diatomic molecules do not occur in nature as single atoms because the molecules formed are more stable than the individual atoms. Bromine (Br 2), iodine (I 2), chlorine (Cl 2), hydrogen (H 2), oxygen (O 2), and fluorine (F 2) are all diatomic molecules

Single Covalent Bonds • When a single pair of electrons is shared, e. g. hydrogen, a single covalent bond is formed.

Lewis Structures • Lewis structures - use dot structures to show electrons are arraigned in molecules. • A shared pair of electrons known as the bonding pair, can be represented as a pair of dots or a line.

• a lone pair is a valence electron pair without bonding or sharing with other atoms. • They are found in the outermost electron shell of an atom. • Electron pairs are considered lone pairs if two electrons are paired but are not used in chemical bonding.

Multiple Covalent Bonds - Many molecules gain a noble gas configuration by sharing more than one pair of electrons, forming multiple covalent bonds. Carbon, nitrogen, oxygen, and sulfur most often form multiple bonds.

Carbon, nitrogen, oxygen, and sulfur most often form multiple bonds.

Multiple Covalent Bonds • Double and triple covalent bonds are examples of multiple bonds. • A double bond occurs when two pairs of electrons are shared. e. g. O 2.

Multiple Covalent Bonds • Double and triple covalent bonds are examples of multiple bonds. • A triple bond occurs when three pairs of electrons are shared. e. g. N 2.

Strength of Covalent Bonds • The strength of covalent bonds depends on how much distance separates the bonded nuclei. • This is called the bond length.

Strength of Covalent Bonds • Since multiple bonds have a shorter bond length. • Single bonds (F 2) are weaker than double bonds (O 2) • Double bonds are weaker than triple bonds (N 2)

• Bond dissociation energy is the amount of energy needed to break a covalent bond. • Breaking bonds always requires the addition of energy.

• Endothermic reactions occur when a greater amount of energy is required to break the existing bonds than is released when the new bonds form in the product molecules.

Exothermic reactions occur when more energy is released forming new bonds than is required to break the bonds in the initial reaction.

9. 2 Naming Molecules • Naming Binary Compounds • 1. The first element in the formula is always named first. • 2. The second element is named using the root of the element and adding the suffix -ide. • 3. Prefixes are used to indicate the number of atoms of each type that are present in the compound. • Note: One exception is that the first element never uses the prefix mono- CO is carbon monoxide, not mono carbon monoxide.

Common Names:

Naming Acids • • An acid is a compound that produces hydrogen ion (H+) in solution. Naming Binary Acids Binary acid- contains hydrogen and one other element e. g. HCl (hydrochloric acid) 1. Use the prefix hydro- to name the hydrogen portion of the compound. 2. Use the root of the second element plus the suffix -ic. e. g. HCl would be hydrochloric acid.

Try These • • HBr HF H 2 S HI

Try These • • HBr - hydrobromic acid HF - hydrofluoric acid H 2 S - hydrosulfuric acid HI - hydroiodic acid

Naming Acids • Note: If the acid contains a polyatomic ion that does not contain oxygen, the acid is named the same way as a binary acid except the root for the second part of the name is the root of the polyatomic ion • e. g. HCN, which is composed of hydrogen and the polyatomic ion cyanide, would be named hydrocyanic acid.

Naming Acids • Naming oxyacids • oxyacid- an acid that contains an oxyanion (poly atomic ion that contains oxygen).

Naming Oxyacid • 1. Identify the anion present. • 2. The name of the oxyacid consists of a form of the root of the anion, a suffix, and the word acid. • 3. If the anion suffix is -ate, it is replaced with the suffix -ic. If the anion ends in -ite, it is replaced with the suffix -ous. • EX: The oxyacid HNO 3 has nitrate (NO 3 -) as its oxyanion. Following the rule it would be named nitric acid. • EX: The oxyacid HNO 2 has nitrite (NO 2 -) as its oxyanion. Following the rule it would be named nitrous acid.

Try these acids • HNO 3 • HNO 2 • H 2 CO 3 • H 2 SO 4 • H 2 SO 3

Try these acids • HNO 3 • HNO 2 - nitric acid - nitrous acid • H 2 CO 3 - carbonic acid • H 2 SO 4 • H 2 SO 3 - sulfuric acid - sulfurous acid

Naming Acids Hints • Ic I ate an oxyacid, It was dangerous, but I’m ite

Naming Acids Hints • Do not use prefixes (mono, di, tri etc) • The most common polyatomic ions are the ones that end in ate. They contain 3 or 4 oxygens. If the first letter of the (ate) polyatomic ion begins with A-O it contains 3 oxygens, if the first letter of the (ate) polyatomic ion begins with P-Z it contains 4 oxygens. E. g NO 3, Cl. O 3, CO 3; PO 4, SO 4.

Naming Acids Hints • The ite polyatomic ions have one less oxygen than their ate counterparts. e. g. Cl. O 3 is chlorate and CLO 2 is chorite, NO 3 is Nitrate and NO 2 is nitrite, PO 4 is phosphate, PO 3 is phosphite, SO 4 is sulphate, SO 3 is sulphite

Acid Naming Game • Rules. 1. Roll one die and combine with hydrogen to get acid. 2. Write correct formula and name of acid. 3. Other players will check for correctness. 1 st player to get 3 acids correctly wins.

Dot Diagrams For Molecules and Polyatomic Ions Step 1 - Sum the valence electrons for all atoms in the molecule. (Use Periodic Table) • For Anions - Add an electron for each negative charge. • For Cations – Subtract an electron for each positive charge.

• Step 2 – Write the symbols for the atoms to show which atoms are attached to which, and connect them with a single bond. – Single bond – represents 2 electrons

• Step 3 – Complete the octets of the atoms bonded to the central atom ( hydrogen can have only 2 electrons).

• Step 4 - Place any leftover electrons on the central atom, even if doing so results in more than an octet.

• Step 5 – If there are not enough electrons to give the central atom an octet, try multiple bonds.

• • • Dot Diagrams For Molecules and Polyatomic Ions Step 1 - Sum the valence electrons for all atoms in the molecule. (Use Periodic Table) For Anions - Add an electron for each negative charge. For Cations – Subtract an electron for each positive charge. Step 2 – Write the symbols for the atoms to show which atoms are attached to which, and connect them with a single bond. – Single bond – represents 2 electrons Step 3 – Complete the octets of the atoms bonded to the central atom ( hydrogen can have only 2 electrons). Step 4 - Place any leftover electrons on the central atom, even if doing so results in more than an octet. Step 5 – If there are not enough electrons to give the central atom an octet, try multiple bonds.

9. 4 Molecular Shape VSEPR Model- Valence Shell Electron Pair Repulsion model • – Linear • – Trigonal planer • – Tetrahedral • – Bent • – Pyramid

Polar Covalent Bonds • If a covalent bond formed between atoms of different elements does not have equal sharing of electron pairs, it is said to be polar covalent. • When a polar bond forms, the shared pair of electrons is pulled towards one of the atoms and a partial charge forms at the end of the atom.

Polar Covalent Bonds

Polar Covalent Bonds

Molecular Shape • VSEPR Model- Valence Shell Electron Pair Repulsion model • Many chemical reactions, depend on the ability of two compounds to come in contact with each other. • The shape of a molecule determines whether or not molecules can get close enough to react. •

Linear Trigonal planer Tetrahedral Bent Pyramid

• The repulsions among electron pairs results in atoms exhisting at fixed angles to each other. • The angle formed between two terminal atoms and the central atom is the Bond Angle

Molecules that contain no lone pairs • When two pairs are shared off the central atom the bond angle is 180 o and the shape is linear (Ba. Cl 2)

Molecules that contain no lone pairs • Three bonding pairs will seek the maximum separation forming a bond angle of 120 O (Al. Cl 3) and the shape is trigonal planer.

Molecules that contain no lone pairs • When the central atom has four bonding pairs (CH 4) the shape is tetrahedral with bond angles of 107. 3 O

Molecules with lone pairs • Lone pairs take up a greater amount of space than shared pairs. The geometry of PH 3 is trigonal pyramidal

Molecules with lone pairs • A water molecule has two single covalent bonds. And two lone pairs. The water molecule has a bent shape with a bond angle of 104. 5 O

Bonding

Bonding

Bonding

Bonding

1. If the electronegativity difference (usually called ΔEN) is less than 0. 5, then the bond is nonpolar covalent. 2. If the ΔEN is between 0. 5 and 1. 6, the bond is considered polar covalent 3. If the ΔEN is greater than 1. 6, then the bond is ionic.

Use the electronegativity difference ΔEN to • Predict the type of bond that forms between. • K and O H and F • H and O Fr and F • Mg and N N and O • Mn and Cl Al and Cl • Pb and O C and I

Solubility of Polar Molecules Surficant Properties of Covalent Compounds Intermolecular forces (van der Waals forces)

Properties of covalent bonds • Molecules are either polar or non polar one way to distinguish between polar and non polar is that non polar molecules are not attracted to an electrical field

Solubility of Polar Molecules • Like dissolves like • Non polar molecules are only soluble in non polar substances. • Polar and ionic substances are usually soluble in polar substances • oil and water don’t mix, why?

Intermolecular forces • The weak forces of attraction between molecules are called intermolecular forces (van der Waals). These forces are much weaker than the forces holding the molecule together.

Intermolecular forces • Many properties of molecules are due to intermolecular forces. • Low melting and boiling points • Hardness- many covalent compounds are relatively soft when in solid form e. g. paraffin wax.

• http: //www. youtube. com/watch? v=0 UAMb P 8 r 9 VU • http: //www. youtube. com/watch? v=1 lnjg 81 da. Bs • http: //www. youtube. com/watch? v=7 DZP 92 X_n 2 I • http: //www. youtube. com/watch? v=45 yabrn ry. Xk&NR=1&feature=fvwp