Chemistry Unit 3 Section 2: Covalent Bonds

​Lesson 3.3 Covalent Bonds

Multiple Choice

"Chemical compounds tend to form so that each atom has an octet (8) electrons in their highest occupied energy level" is known as what

• The Octet Rule

• The rule of 8

• An Electron Flush

• The Balanced Charge Law

Multiple Choice

When an atom loses an electron, it becomes a

• positive ion

• negative ion

Multiple Choice

Ionic bonds form between metals and ____.

• metalloids
• metals
• nonmetals

Lesson Objectives

• Explain how nonmetals share electrons to form bonds

• Distinguish between single, double, & triple bonds

• Draw electron dot structures for molecules

• Describe the difference between polar and nonpolar covalent bonds

​Molecular Compounds

• Covalent Bonds: bonds between nonmetal atoms that share some or all of their valence electrons

• Molecule: A neutral group of atoms held together by one or more covalent bonds

  • Can be two or more of one atom, or two or more different atoms

    • ​Diatomic molecule: A molecule containing only two of the same atoms

​Covalent vs Ionic

• Covalent Bonds Share Electrons

  • ​Covalent Bonds Cooperate and Share

  • Two non-metals

  • Low Melting/Boiling Points

  • Bonds are strong, but not as strong as ionic

• Ionic Bonds involve one atom losing electrons an another gaining electrons

  • Ionic Bonds- It's all about me, I will Take what I want​

  • A metal and a non-metal

  • High Melting/Boiling Points

  • Conduct Electricity

​Molecular Compounds

• There are many different models to show molecules

• One model show the different orbitals of the atoms combining into hybridized orbitals to make different shapes

​The Octet Rule in Molecules

• When nonmetals bond together, they don't gain or lose electrons, but share

• In general, Atoms still want to have 8 electrons in their valence shell to be stable

  • Exceptions:

    • Hydrogen only needs 2

    • Boron Only Needs 6

    • Sulfur and Phosphorus can have up to 12

• The number of Valence Electrons relates to the Group numbers

  • Group 1 Has 1

  • Group 2 has 2

  • Group 13-17 has (group number-10)​

Fill in the Blank

How many Valence electrons are in Group 16?

Fill in the Blank

How many Valence electrons are in Group 13?

​Electron Dot Structure

• ​Electron-Dot Notation: shows only the valence electrons of an atom, indicated by dots around the element symbol

  • Used to show the shared electrons in a molecule

  • Each Bond between atoms is made up of at least 2 electrons

    • More electrons in a bond make a bond stronger/harder to break

    • Different types of Bonds

      • Single Covalent Bond: a bond made of one pair of electrons

      • Double Covalent Bond: A bond made of two pairs of electrons

      • Triple Covalent Bond: A bond Made of three pairs of electrons

​Electron Dot Structure Rules

• ​If Carbon is present, it always goes in the middle

• Hydrogen and Halogens go on the outside

• Start placing your electrons and filling the outer atoms before the central atoms​

• ​One Dot shows a single electron

• A bar shows two electrons​

​Electron Dot Structure Sample 1

• ​Draw an electron dot structure for the diatomic molecule H₂

  • Step 1: Identify the number of Valence electrons in all atoms of the molecule

    • Hydrogen is in Group 1 and has 1 valence electron

    • We have 2 Hydrogens, so we have 2 valence Electrons Total

  • Step 2: Write the Elemental Symbols with a bit of space between them

  • Step 3: Start placing your electrons, starting with a bond formed by TWO Electrons

  • Step 4: Once all electrons are placed, Check to see that all atoms have 8 electrons around them

    • Two if it is hydrogen

​Electron Dot Structure Sample 2

• ​Draw an electron dot structure for the diatomic molecule H₂O

  • Step 1: Identify the number of Valence electrons in all atoms of the molecule

Fill in the Blank

How many Valence Electrons does one Hydrogen have?

Fill in the Blank

How many Valence Electrons does one Oxygen have?

​Electron Dot Structure Sample 2

• ​Draw an electron dot structure for the diatomic molecule H₂O

  • Step 1: Identify the number of Valence electrons in all atoms of the molecule

    • Hydrogen is in Group 1 and has 1 valence electron

    • Oxygen is in Group 16 and has 6 Valence Electrons

    • Total amount of Valence Electrons: 1+1+6=8

  • Step 2: Write your elemental symbols

    • Hydrogen can never go in the middle!

  • Step 3: Connect the atoms with single atomic bonds, then place other electrons so that each atom has a full number of electrons

  • Step 4: Double Check Your Work

​Electron Dot Structure Sample 3

• ​Draw an electron dot structure for the diatomic molecule HOCl

  • Step 1: Identify the number of Valence electrons in all atoms of the molecule

    • Hydrogen is in Group 1 and has 1 valence electron

    • Oxygen is in Group 16 and has 6 Valence Electrons

    ​

Fill in the Blank

How many Valence Electrons does Chlorine Have?

​Electron Dot Structure Sample 3

• ​Draw an electron dot structure for the diatomic molecule HOCl

  • Step 1: Identify the number of Valence electrons in all atoms of the molecule

    • Hydrogen is in Group 1 and has 1 valence electron

    • Oxygen is in Group 16 and has 6 Valence Electrons

    • Chlorine is in Group 17 and has 7 Valence Electrons

    • Total amount of Valence Electrons: 1+6+7=14

  • Step 2: Write your elemental symbols

  • Step 3: Connect the atoms with single atomic bonds, then place other electrons so that each atom has a full number of electrons

  • Step 4: Double Check Your Work

Multiple Choice

A neutral group of atoms that are held together by covalent bonds is called what?

• An Ion

• A Molecule

• A Particle

• An Atom

Multiple Choice

How many atoms are in a diatomic molecule?

• 1

• 2

• 8

• 10

Multiple Choice

How many VALENCE ELECTRONS does Chlorine have?

• 2

• 7

• 8

• 10

• 17

​Electronegativity & Bonding

• ​In covalent bonds, both atoms pull on electrons

  • The Pull is not equal between the two electrons

    • Think Tug-of-War​

• Electronegativity: The ability of an atom to attract electrons towards itself in a chemical bond

  • A Higher electronegativity means an atom can pull electrons to it more

• Electronegativity follows a trend where it increases as you move across the period, and decreases as you move down

  • Fluorine is the most electronegative element with a value of 4.0​

​Electronegativity Trends

​Electronegativity & Bond Types

• Covalent bonds fall into two categories depending on how much each atom pulls

  • Non-polar Covalent Bonds:​ a bond where electrons are shared "equally"

    • Electronegativity is less than 0.4

  • Polar Covalent Bonds: Electrons are shared unequally with one side positive and the other negative

    • Electronegativity difference is between 0.4 and 2.0

  • If the electronegativity is greater than 2.0, the bond is ionic

​Electronegativity & Types of Bonds

​Calculating Electronegativity Differences Sample Problem 1

• Calculate the Electronegativity difference in the bonds between K and F, and determine if it is polar or non-polar

  • Step 1: Find the electronegativity of​ the two elements

    • K=0.8

    • F=4.0

  • Step 2: subtract the smaller value from the larger value

    • 4.0-0.8

Fill in the Blank

Calculate the Electronegativity difference in the bonds between K and F.

​Calculating Electronegativity Differences Sample Problem 1

• Calculate the Electronegativity difference in the bonds between K and F, and determine the bond type.

  • Step 1: Find the electronegativity of​ the two elements

    • K=0.8

    • F=4.0

  • Step 2: subtract the smaller value from the larger value

    • 4.0-0.8=3.2

  • Step 3: Compare to the values for polar and non-polar to determine the bond type

Multiple Choice

What type of bond is the Bond between K & F?

• Polar

• Non-polar

• Ionic

​Calculating Electronegativity Differences Sample Problem 2

• ​Use the electronegativity differences to classify bonding between sulfur (S) and Hydrogen

  • Step 1: Find the electronegativity of​ the two elements

    • S=2.5

    • H=2.1

  • Step 2: subtract the smaller value from the larger value

Fill in the Blank

Calculate the Electronegativity difference in the bonds between Sulfur and Hydrogen.

.

​Calculating Electronegativity Differences Sample Problem 2

• ​Use the electronegativity differences to classify bonding between sulfur (S) and Hydrogen

  • Step 1: Find the electronegativity of​ the two elements

    • S=2.5

    • H=2.1

  • Step 2: subtract the smaller value from the larger value

    • 2.5-2.1=0.4

Multiple Choice

Is the Bond between Sulfur & Hydrogen Ionic, Polar or Non-polar?

• Polar

• Non-polar

• Ionic

Multiple Choice

Electronegativity is...

• how good an atom is at attracting electrons
• the ability of an atom to lose electrons
• the energy required to remove an electron from a specific atom
• how easy it is to make friends. 

Multiple Choice

What two types of atoms make a covalent bond?

• 2 non-metals

• 1 metal and 1 non-metal

• 2 metals

Multiple Choice

The element with the largest electronegativity is - 

• At
• F
• Cl
• Br