COVALENT BONDING CHEMICAL FORMULA Vocabulary Chemical Formula Molecular

COVALENT BONDING & CHEMICAL FORMULA Vocabulary Chemical Formula Molecular Compound Molecular Formula Molecule Ionic compound Formula Unit Bond Energy Electron Dot Notation Lewis Structure Structural Formula Covalent Bond Electronegativity Single Bond Double Bond Multiple Bond

COVALENT BONDING & CHEMICAL FORMULA A little Review: What is a Chemical Formula? • Indicates # of atoms of each element in a compound using the element Symbols and subscripts • Examples: • H 2 O • Na. Cl

COVALENT BONDING & CHEMICAL FORMULA A little Review: What is the difference between a MOLECULAR FORMULA & a FORMULA UNIT ? CHEMICAL FORMULA Molecular Compounds (Covalent) Molecular Formula - Formula for a stable group of atoms which exists as a package. Ionic Compound – Compound created by transferring electrons Unit Formula- simplest part of a crystal structured compound

COVALENT BONDING & CHEMICAL FORMULA A little Review: What is the difference between a MOLECULAR FORMULA & a FORMULA UNIT ? 1 Na Molecules act as individual lumps of substance. Molecular Formula: H 2 O 1 Cl Ionic compounds are part of a geometric crystal structure. The Unit formula is the most simple component of the structure which repeats Unit Formula: Na. Cl

COVALENT BONDING & CHEMICAL FORMULA A little Review: What is a Chemical Formula? • Indicates # of atoms of each element in a compound using the element Symbols and subscripts • Examples: • H 2 O • Na. Cl

COVALENT BONDING & CHEMICAL FORMULA What is a Covalent Bond? Its all about sharing Electrons Some atoms share nicely (equally) . . . while some atoms do not share equally or not at all.

COVALENT BONDING & CHEMICAL FORMULA What is a Covalent Bond? How can you tell how well the atoms are sharing? • Electronegativity tells how much atoms take electrons • Higher Electonegative Atoms keep electrons more • Low Electronegtaive Atoms keep electrons less

COVALENT BONDING & CHEMICAL FORMULA What is a Covalent Bond? How can you tell how well the atoms are sharing? When the Difference in EN in the atoms bonded is less than or equal to. 3 |EN 1 – EN 2| ≤. 3 Example: Bond between H and S EN of H = 2. 1 EN of S = 2. 4 |EN 1 – EN 2| = |2. 1 – 2. 4| =. 3 ≤. 3 This says that H and S will share equally.

COVALENT BONDING & CHEMICAL FORMULA What is a Covalent Bond? How can you tell how well the atoms are sharing? The most equal sharing will be between atoms of the same element in a diatomic molecule such as H 2. |EN 1 – EN 2| ≤. 3 Example: Bond between H and S EN of H = 2. 1 |EN 1 – EN 2| = |2. 1 – 2. 1| = 0 ≤. 3 This says there will be perfect sharing.

COVALENT BONDING & CHEMICAL FORMULA What is a Covalent Bond? .

COVALENT BONDING & CHEMICAL FORMULA Electronegativity for other types of Bonds? Other bonds exist. They are not strictly defined but rather cover a range of EN differences as follows: Ionic - EN difference < 1. 7 Polar Covalent – from. 3 to 1. 7 Covalent – below. 3

COVALENT BONDING & CHEMICAL FORMULA Electronegativity for other types of Bonds? Equal Sharing Unequal Sharing No sharing Equal charge on atoms Atom with higher EN becomes slightly negative Full charge on each component (ion)

COVALENT BONDING & CHEMICAL FORMULA What is a Covalent Bond? Why do atoms form bonds? • • Atoms are more stable with full outer shells. Atoms prefer Noble Gas arrangements of electrons Atoms share, borrow or steal to become stable. This is called the Octet Rule: Atoms prefer outer shells (which is usually 8 electrons. )

COVALENT BONDING & CHEMICAL FORMULA What is a Covalent Bond? Hydrogen gains a full outer shell by sharing an electron with a partner atom.

COVALENT BONDING & CHEMICAL FORMULA What is a Covalent Bond? With Oxygen two pair of electrons are shared, so a DOUBLE BOND is formed. The Double Bond is represented by a double dash.

COVALENT BONDING & CHEMICAL FORMULA What is a Covalent Bond? With Nitrogen three pair of electrons are shared, so a TRIPLE BOND is formed. The Triple Bond is represented by a triple dash.

COVALENT BONDING & CHEMICAL FORMULA You will need to remember how to draw the Electron-dot (Lewis Structure) notation for the elements from the PT.

COVALENT BONDING & CHEMICAL FORMULA Electron Accounting: Draw the Lewis Structure for CH 3 Br: 1. Determine the # or each atom in the molecule: C = 1, H = 3, Br = 1 2. Write the Electron Dot Notation for each atom. 3. Determine the total number of valence electrons available: C H Br 4 + 3(1) +7 = 18 electrons 4. Arrange the atoms to form a skeleton of the molecule. If C is present, it is the central atom. If not the least EN atom is central. H is never central. 5. Replace paired of electrons between atoms with dash to represent bond. 6. Check your work. * Count electrons in structure to check the # matches # available. * Be sure atoms have octet (except H)

COVALENT BONDING & CHEMICAL FORMULA How strong are the Bonds? Bond strengths can be determined by the length of the bond. The length of the bond is the distance between the atoms. Longer bonds are weaker. Shorter bonds are stronger.

COVALENT BONDING & CHEMICAL FORMULA Covalent Bonds and Electron Configuration – When bonding occurs orbitals overlap.