Covalent Bonds Atoms can form molecules by sharing electrons in the covalent bond. This is done only among non-metal atoms.

Molecules Some elements in nature are found in the form of molecules Diatomic = 2 atoms BrINClHOF Compound composed Of molecules is called a Molecular compound

PROPERTIES Relatively low melting points and boiling points Many are gases and liquids at room temperature Composed of atoms of 2 or more nonmetals

Molecular Formulas Show how many atoms of each element a molecule contains Ex. H2O has 2 hydrogen atoms and 1 oxygen atom Doesn’t show shape of molecule or which atoms are covalently bonded and how

Dot Structures-Octet Rule (All atoms want 8 electrons around them.) Valence electrons are those in the outermost orbitals. They are the ones that can form bonds. Electron sharing occurs in such a way so that atoms attain the electron configuration of the noble gases.

H H SINGLE COVALENT BONDS Two atoms held together by sharing a pair of electrons. Can be shown by lewis dot or a dash H H

UNSHARED PAIRS In F2 each flourine contributes one electron The electrons that are not shared are called Unshared pairs, lone pairs or nonbonding pairs

Draw Lewis structures NH3 PCl3 Cl2 SBr2

DOUBLE AND TRIPLE COVALENT BONDS Occurs when three pairs of electrons Are shared Occurs when two pairs of electrons are shared

NASL Method for Lewis Dot Structures Helps to determine how to place electrons around an atom ( double/triple bonds + lone pairs) Exceptions to octet = H = 2, Be = 4, B= 6 STEPS Write a skeleton molecule with the lone atom in the middle (Hydrogen can never be in the middle) Calculate (N) Needed which is the sum of electrons needed for all atoms to obey the octet rule.

NASL Method Show structure for CO2 O C O skeleton 2. Needed electrons C = 1 x 8 = 8 O = 2 x 8 = 16 N = 24

NASL METHOD Step 3; Calculate A (Available) = sum of all valence electrons. For anions and cations you need to subtract or add electrons here. Step 4; Calculate S ( Shared) = Difference between N and A

CO2 Shared Needed – Available = 24-16= 8 1 x 4 = 4 for Carbon 2 x 6 = 12 for Oxygen 16 A (available) Shared Needed – Available = 24-16= 8

NASL Method Divide S by 2 to obtain the number of bonds to be extended from the central atoms. 8 / 2 = 4 O::C::O Calculate L ( Lone-pair electrons ) the difference between A and S 16 – 8 = 8 .. .. O::C::O ●● ●●

Let's Try it! H O H S Water H2O N 2 x 2 = 4 for Hydrogen 1 x 8 = 8 for Oxygen 4+8=12 needed electrons 12 N - 8 H 2 x 1 = 2 for Hydrogen 1 x 6 = 6 for Oxygen You have 8 available electrons - 4 B 4 NB 12 – 8 = 4/2 = Bonding H:O:H 8 – 4 = 4 non-bonding electrons .. H:O:H ●● .. H:O:H ●●

Let's Try it! H H N H S Ammonia NH3 N 3 x 2 = 6 for Hydrogen 1 x 8 = 8 for Nitrogen 6+8=14 needed electrons 14 N - 8 H 3 x 1 = 3 for Hydrogen 1 x 5 = 5 for Nitrogen You have 8 available electrons - 6 B 2 NB 14 – 8 = 6/2 = 3 bonding pairs H .. H:N:H 8-6 = 2 lone electrons H H .. H:N:H ●● .. H:N:H ●●

REVIEW Draw lewis dot structures for the following PCL3 CH4

Review Quiz #2 Using NASL Show covalent bonding for the following compounds. Show all work for credit. ( 6 points ) SO2

Nomenclature Naming of Binary Molecular Compounds Binary Compounds: Composed of two different elements that are nonmetals. Ex. CO and CO2 (not carbon Oxide) CO = Carbon monoxide = poisonous gas CO2 = carbon dioxide waste product of breathing Need to differentiate different types of compounds by using prefixes. Tells you how many of each element are present Mono = 1 Penta = 5 Di = 2 Hexa = 6 Tri = 3 Hepta = 7 Tetra = 4 Octa = 8

Naming Guidelines 1. make sure you have a binary molecular compound composed of two nonmetals 2. Name must identify the elements and how many are present 3. Name the elements in the order listed 4. Omit the prefix – mono when the first element only has one Ex. SF6 is sulfur hexaflouride NOT monosulfur hexaflouride 5. The suffix for the second element is -ide

Writing Formulas Use the prefixes in the name to determine the correct subscripts for the formula. Ex. Silicon Carbide ( no prefixes so must contain one of each) SiC Dinitrogen Tetroxide = N2O4

Let’s Practice! Phosphorus Pentachloride Iodine Heptaflouride Chlorine triflouride OF2 SO2 N2O4

Using a few sentences discuss what the cartoon might mean in terms of how Cl and H bond

POLARITY Covalent bonds involve atoms sharing electrons (pulled in a tug of war) When electrons are pulled equally = nonpolar Covalent bond When electrons are pulled unequally = polar covalent bond

Electronegativity The magnitude of attraction for electrons is called “Electronegativity”. The more electronegative an atom is, the more it wants the electrons.

The higher the electronegativity Value the greater the ability to attract electrons

Bond types WATER IS A POLAR MOLECULE O = 3.5 ELECTRONEGATIVE H = 2.1 ELECTRONEGATIVE DIFFERENCE = 1.4 = POLAR COVALENT OXYGEN PULLS HYDROGENS ELECTRONS CLOSER THAN HYDROGEN CAN PULL OXYGENS ELECTRONS. OXYGEN GETS AN OVERALL PARTIAL NEGATIVE CHARGE AND HYDROGEN GETS AN OVERALL PARTIAL POSTITIVE CHARGE DESIGNATED BY A GREEK DELTA SIGN

VSEPR Theory Electron dot structures fail to reflect the 3-dimensional shape of molecules Molecules in reality are 3 dimensional and can be explained by the VSEPR theory

VSEPR Theory Explains 3-D shape of molecules Based on the theory that repulsion occurs between electron pairs and causes a variety of molecular shapes. Electrons want to stay as far apart as possible Can be determined by first looking at the lewis dot structure Counting how many electron clouds (pairs) are radiating

LINEAR MOLECULES The simplest structure has two groups around the central atom. Carbon monoxide, CO2, is an example of this kind of shape. The two groups of electrons in the two double bonds repel each other and assume a shape with an angle of 180 degrees.

MOLECULAR SHAPES

Review Pyramidal = 3 bonding pairs And a lone pair Trigonal planar = 3 bonding No lone pairs