Covalent Bonding - Henry County School District

Covalent Bonding - Henry County School District

No Bellwork 10/13/15 Review your grade report. Questions after class. Missing assignments before 9/11 worth 50% Missing assignments 9/12-10/9 must be turned in by this Friday (10/16) After Friday, anything before 10/9 worth 50% Have parent/guardian sign grade report by Friday for extra credit ***Ionic Bonding & Naming Schoology Test will be available later today (due Tues 10/20 9am) 1 Covalent Bonding Chapter 8 2

8.1 Molecular Compounds Covalent Bond are atoms held together by sharing electrons. Molecule is a neutral group of atoms joined together by covalent bonds. Diatomic molecule is a molecule consisting of two atoms Molecular compound is a compound composed of molecules. Example: water has two covalent bonds, the smallest particle of water is called a water molecule, and is a molecular compound 3 8.1 Molecular Compounds Molecular compounds tent to have relatively lower

melting and boiling points that ionic compounds Most are gases or liquids at room temperature, and most molecular compounds are composed of two or more nonmetals. Molecular formula is the chemical formula of a molecular compound Example: Waters formula is H2O A molecular formula shows how many atoms of each element a molecule contains 4 8.2 The nature of Covalent Bonding In covalent bonds, electrons sharing usually occur so that atoms attain the electron

configuration of noble gases. In covalent bonds elements usually acquire a total of eight electrons (an octet) by sharing electrons. Single covalent bond is when atoms are held together by sharing a pair of electrons 5 8.2 The nature of Covalent Bonding An electron dot structure can be used to represent the shared pair of electrons of the covalent bond by two dots. Structural formula represents covalent bonds by dashes and shows the arrangement of covalently bonded atoms. Unshared pair (or lone pair) is a pair of valence

electrons that is not shared between the atoms 6 8.2 The nature of Covalent Bonding Single covalent bond example Water: The oxygen atom has two unshared pair of electrons and two single covalent bonds. 7 8.2 The nature of Covalent Bonding Atoms form double or triple covalent bonds if they can attain a noble gas structure by sharing two pairs or three pairs of electrons.

Double covalent bond is a bond that involves two shared pairs of electrons Triple covalent bond is a bond that involves three shared pairs of electrons 8 Steps for Building Lewis Structures 1. Decide on a central atom. Generally the LEAST electronegative atom is central atom. Hydrogen can NEVER be central atom because it can only form one bond. 2. Add up the number of valance electrons for ALL elements in compound 3. Form a single bond between the central atom and each of the other atoms 4. Add lone pair to elements to complete the octet (remember Hydrogen only want 2 electrons) 5. Check each element to make sure they have access to 8 electrons (H =

2). Ask are they happy? 6. Add up the number of electrons in drawing [count dots + 2(# of lines)] and see if this number match the number of valance electrons in step 2 If you have too many form double or triple bonds as needed If you have too few than you made a mistake in your drawing. 9 Carbon Carbon Dioxide, Dioxide, CO CO22 1. Central atom = 2. Valence electrons = 3. Form bonds. O

C O C 4 eO 6 e- X 2 Os = 12 eTotal: 16 valence electrons This leaves 12 electrons (6 pair). 4. Place lone pairs on outer atoms. 5. Check to see that all atoms have 8 electrons around it except for H, which can have 2. Carbon Carbon Dioxide, Dioxide, CO

CO22 C 4 eO 6 e- X 2 Os = 12 eTotal: 16 valence electrons How many are in the drawing? 6. There are too many electrons in our drawing. We must form DOUBLE BONDS between C and O. Instead of sharing only 1 pair, a double bond shares 2 pairs. So one pair is taken away from each atom and replaced with another bond. O O

C C O O

O C O

How many double bonds is Carbon making? How many double bonds is one Oxygen making? How many lone pairs are on Oxygen? Carbon? 11 Now Now You You Try Try One! One! Draw Draw Carbon Carbon tetrachloride tetrachloride 1. Central atom is Carbon 2. One C = 4 e-, Four Cl = 4 (7e-) Total: 32 e3. Form single bonds

4. Add Lone Pairs 5. Carbon has 4 single bond and is happy, each Chlorine has 1 single bond and 3 lone pairs and is happy 6. Check electrons used 24 dots + 2 (4 lines) = 32 eStructure is correct Now Now You You Try Try One! One! Draw Draw Sulfur Sulfur Dioxide Dioxide 1. Central atom is Sulfur

2. One S = 6 e-, Two O = 2 (6 e-) Total: 18 e3. Form single bonds 4. Add Lone Pairs 5. Sulfur has 2single bond and 2 lone pairs and is happy, each Oxygen has 1 single bond and 3 lone pairs and is happy 6. Check electrons used 16 dots + 2 (4 lines) = 20 eStructure is NOT Correct Make double bonds Check electrons used 12 dots + 2 (3 lines) = 18 structure is correct Diatomic Molecules There are 7 elements that do not exist in nature as a single atom; they always appear as pairs When atoms turn into ions, this NO LONGER HAPPENS! They can

form bonds as single atoms. Hydrogen H2 Nitrogen N2 Oxygen O2 Fluorine F2 Chlorine Cl2 Bromine Br2 Iodine I2 Remember: BrINClHOF Or remember the 7 elements in the shape of a 7 on the periodic table 14 8.4 Polar Bonds and Molecules Nonpolar covalent bond (nonpolar bond) is when the bonding electrons are shared equally.

ALL diatomic halogen molecules are nonpolar Polar covalent bond (polar bond) is when the bonding electrons are NOT shared equally The more electronegative atom attracts electrons more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge. When polar molecules are placed between oppositely charges plates they tend to become oriented with respected to the positive and negative plates. 15 8.4 Polar Bonds and Molecules To determine if a bond is polar or nonpolar look at the difference in electronegativity values Nonpolar covalent is electronegativity difference range of 0.0 to 0.5 polar covalent is electronegativity difference range of

0.51 to 1.6 Ionic bonds is electronegativity difference range above 1.7 to 4.0 16 17 Bond Bond Polarity Polarity HCl is POLAR because it has a positive end and a negative end. (difference in electronegativity) +d -d

H Cl Cl has a greater share in bonding electrons than does H. Cl has slight negative charge (-d) and H has slight positive charge (+ d) 18 Bond Bond Polarity Polarity

This is why oil and water will not mix! Oil is nonpolar, and water is polar. The two will repel each other, and so you can not dissolve one in the other 19 Bond Bond Polarity Polarity Like Dissolves Like Polar dissolves Polar Nonpolar dissolves Nonpolar 20

Compare and contrast Ionic and Covalent bonds Characteristic Reason for forming Ionic Bonds Covalent Bonds Because atoms want to have full outer energy levels How they form Transferring Sharing Electrons Electrons Strength of bond

Very Strong Weak Bond Bond Melting/Boiling Points Very High Low Phase at room temperature Most are solids Most are liquids or gases 21 Lewis Structure Summary The elements MOST of the time follow the guide

lines below. There are a few exceptions Carbon will form 4 bond Nitrogen and Phosphorous will form 3 bonds and will have 1 lone pair Oxygen, sulfur and Selenium will form 2 bonds and have 2 lone pairs F, Cl, Br, and I will form 1 bond and have 3 lone pairs. Hydrogen will from 1 bond The bonds can be any combination of single, double or triple bonds. 22

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