Molecules and Molecules and BondingBondingDanielsDaniels

Sims Fayola Sims Fayola

How are molecules How are molecules represented?represented?

Chemical formulaChemical formula = symbols for the = symbols for the elements are used to indicate the types elements are used to indicate the types of atoms present and subscripts are used of atoms present and subscripts are used to indicate the relative numbers of atoms.to indicate the relative numbers of atoms.

EXAMPLEEXAMPLE: CO2: CO2 Structural formulaStructural formula = individual bonds = individual bonds

are shown indicated by lines. are shown indicated by lines.

EXAMPLEEXAMPLE: H-O-H: H-O-H

What are Chemical What are Chemical Bonds?Bonds?

The forces that The forces that hold atoms hold atoms together in together in compounds. compounds.

MUST follow the MUST follow the octet rule!!!octet rule!!!

Types of Bonds…Types of Bonds… Ionic Ionic MetallicMetallic CovalentCovalent Polar CovalentPolar Covalent Non-polar Covalent Non-polar Covalent

(this one is like a (this one is like a covalent bond) covalent bond)

Ionic Bonds…Ionic Bonds… Closely packed, oppositely charged ions.Closely packed, oppositely charged ions.

(+) ion = cation and (-) ion = anion (+) ion = cation and (-) ion = anion Makes the compound electrically neutral Makes the compound electrically neutral

and joined by electrostatic forces.and joined by electrostatic forces. Formed when an atom that loses Formed when an atom that loses

electrons easily (metals) reacts with an electrons easily (metals) reacts with an atom that has a whole lot of electrons atom that has a whole lot of electrons (non-metals). (non-metals).

The most stable and strongest bond! The most stable and strongest bond! EXAMPLES… (NaCl, MgCl2, Na2O)EXAMPLES… (NaCl, MgCl2, Na2O)

Properties of Ionic Properties of Ionic Compounds…Compounds…

Most are 3-D crystalline solidsMost are 3-D crystalline solids Each ion is strongly attracted to each otherEach ion is strongly attracted to each other Conduct electrical current in a molten stateConduct electrical current in a molten state

Metallic Bonds… Metallic Bonds… Metals consist of closely packed cations Metals consist of closely packed cations

(+ charges)(+ charges) Cations are surrounded by mobile Cations are surrounded by mobile

moving valence electronsmoving valence electrons Consist of an attraction of free-floating Consist of an attraction of free-floating

valence electrons to the positively valence electrons to the positively charges metal ionscharges metal ions

Examples are Cu, Fe, Mg and precious Examples are Cu, Fe, Mg and precious metalsmetals

Lets Practice…Lets Practice… Write the symbols for each elementWrite the symbols for each element Draw an arrow to show the transfer of electrons Draw an arrow to show the transfer of electrons

from one atom to the other (lewis structures)from one atom to the other (lewis structures) Determine the charge for each ion and write the Determine the charge for each ion and write the

chemical formulachemical formula 1) Potassium + Fluorine1) Potassium + Fluorine 2) Magnesium + Iodide2) Magnesium + Iodide 3) Sodium + Oxygen3) Sodium + Oxygen 4) Sodium + Chlorine4) Sodium + Chlorine 5) Calcium + Chlorine5) Calcium + Chlorine 6) Aluminum + Chlorine6) Aluminum + Chlorine

Covalent Bonds…Covalent Bonds… Electrons are shared by the 2 nuclei Electrons are shared by the 2 nuclei

of the atoms. of the atoms. Often non-metals form these bonds.Often non-metals form these bonds. All organic molecules are covalent.All organic molecules are covalent. MOST COMMON BOND!!!MOST COMMON BOND!!! But there are 2 types of covalent But there are 2 types of covalent

bonds.bonds.

Polar Covalent Bonds…Polar Covalent Bonds… Unequal sharing of electrons Unequal sharing of electrons

because 2 different atoms (different because 2 different atoms (different electronegativities) electronegativities)

Makes one atom look more (+) and Makes one atom look more (+) and the other atom look more (-) (dipole the other atom look more (-) (dipole moments) moments)

Any molecules that are different can Any molecules that are different can show some polarity. show some polarity.

EXAMPLES… (H2O, ClF, CCl4, HF) EXAMPLES… (H2O, ClF, CCl4, HF)

Non-Polar Covalent Non-Polar Covalent Bonds…Bonds…

When atoms are shared equally because When atoms are shared equally because they are identical atoms. they are identical atoms.

Pretty much the same as regular Pretty much the same as regular covalent. covalent.

Doesn’t make one atom more + or more -Doesn’t make one atom more + or more - EXAMPLES…(H2, O2, N2, Cl2) EXAMPLES…(H2, O2, N2, Cl2)

VSEPR Theory…VSEPR Theory…

The The VValence-alence-SShell hell EElectron-lectron-PPair air RRepulsion Theoryepulsion Theory

Because electron pairs repel the Because electron pairs repel the molecules adjust their shapes so that the molecules adjust their shapes so that the valence-electron pairs are as far apart as valence-electron pairs are as far apart as possible. (why H2O is bent)possible. (why H2O is bent)

Molecular shapes: linear, trigonal planar, Molecular shapes: linear, trigonal planar, bent, pyramidal, tetrahedral, bypyrimidalbent, pyramidal, tetrahedral, bypyrimidal

Covalent Bonding & Covalent Bonding & Lewis Strucutes…Lewis Strucutes…

Single bonds: H2O, NH3, CH4, NF3Single bonds: H2O, NH3, CH4, NF3 Double bonds: CO2, CH3COOH (acetic Double bonds: CO2, CH3COOH (acetic

acid) acid) Triple bonds: N2Triple bonds: N2 There can be some exceptions to the There can be some exceptions to the

rules, but we won’t get into theserules, but we won’t get into these

Let’s Practice…Let’s Practice… Write the symbols for each elementWrite the symbols for each element Rearrange the electrons to pair up or “fit like a Rearrange the electrons to pair up or “fit like a

puzzle” (use different colors for each atom) puzzle” (use different colors for each atom) AKA make the lewis structureAKA make the lewis structure

Draw circles to show the sharing of electronsDraw circles to show the sharing of electrons Write the chemical formula for each moleculeWrite the chemical formula for each molecule

1) Hydrogen + Hydrogen1) Hydrogen + Hydrogen 2) Hydrogen + Oxygen2) Hydrogen + Oxygen 3) Chlorine + Chlorine3) Chlorine + Chlorine 4) Carbon + Oxygen4) Carbon + Oxygen 5) Carbon + Hydrogen5) Carbon + Hydrogen