Chemical BONDING

Chemical Bond A bond results from the attraction of nuclei for electrons –All atoms trying to achieve a stable octet IN OTHER WORDS –the p + in one nucleus are attracted to the e- of another atom Electronegativity

Two Major Types of Bonding Ionic Bonding –forms ionic compounds –transfer of e - Covalent Bonding –forms molecules –sharing e -

One minor type of bonding Metallic bonding –Occurs between like atoms of a metal in the free state –Valence e- are mobile (move freely among all metal atoms) –Positive ions in a sea of electrons Metallic characteristics –High mp temps, ductile, malleable, shiny –Hard substances –Good conductors of heat and electricity as (s) and (l)

It’s the mobile electrons that enable m e - tals to conduct electricity!!!!!!

IONic Bonding electrons are transferred between valence shells of atoms ionic compounds are made of ions ionic compounds are called Salts or Crystals NOT MOLECULES

IONic bonding Always formed between metals and non-metals [METALS ] + [NON-METALS ] - Lost e - Gained e -

IONic Bonding Electronegativity difference > 2.0 –Look up e-neg of the atoms in the bond and subtract NaCl CaCl 2 Compounds with polyatomic ions NaNO 3

Anion (-) Cation (+)

hard 22 o C high mp temperatures nonconductors of electricity in solid phase good conductors in liquid phase or dissolved in water (aq) SALTS Crystals Properties of Ionic Compounds

Covalent Bonding Pairs of e- are shared between non-metal atoms electronegativity difference < 2.0 forms polyatomic ions molecules

Properties of Molecular Substances Low m.p. temp and b.p. temps relatively soft solids as compared to ionic compounds nonconductors of electricity in any phase Covalent bonding

Covalent, Ionic, metallic bonding? NO 2 sodium hydride Hg H 2 S sulfate NH 4 + Aluminum phosphate KH KCl HF CO Co Also study your characteristics!

Drawing ionic compounds using Lewis Dot Structures Symbol represents the KERNEL of the atom (nucleus and inner e-) dots represent valence e -

NaCl This is the finished Lewis Dot Structure [Na] + [ Cl ] - How did we get here?

Step 1 after checking that it is IONIC –Determine which atom will be the + ion –Determine which atom will be the - ion Step 2 –Write the symbol for the + ion first. NO DOTS –Draw the e- dot diagram for the – ion COMPLETE outer shell Step 3 –Enclose both in brackets and show each charge

Draw the Lewis Diagrams LiF MgO CaCl 2 K 2 S

Drawing molecules using Lewis Dot Structures Symbol represents the KERNEL of the atom (nucleus and inner e-) dots represent valence e -

Always remember atoms are trying to complete their outer shell! The number of electrons the atoms needs is the total number of bonds they can make. Ex. … H? O? F? N? Cl? C? one two one three one four

Methane CH 4 This is the finished Lewis dot structure How did we get here?

Step 1 –count total valence e - involved Step 2 –connect the central atom (usually the first in the formula) to the others with single bonds Step 3 –complete valence shells of outer atoms Step 4 –add any extra e - to central atom IF the central atom has 8 valence e - surrounding it.. YOU’RE DONE!

Sometimes... You only have two atoms, so there is no central atom, but follow the same rules. Check & Share to make sure all the atoms are “happy”. Cl 2 Br 2 H 2 O 2 N 2 HCl

DOUBLE bond –atoms that share two e- pairs (4 e-) O TRIPLE bond –atoms that share three e- pairs (6 e-) N

Draw Lewis Dot Structures You may represent valence electrons from different atoms with the following symbols x,, CO 2 NH 3

Draw the Lewis Dot Diagram for polyatomic ions Count all valence e- needed for covalent bonding Add or subtract other electrons based on the charge REMEMBER! A positive charge means it LOST electrons!!!!!

Draw Polyatomics Ammonium Sulfate

Covalent Bonds Types of Covalent Bonds NON-Polar bonds –Electrons shared evenly in the bond –E-neg difference is zero Between identical atoms Diatomic molecules

Types of Covalent Bonds Polar bond –Electrons unevenly shared –E-neg difference greater than zero but less than 2.0 closer to 2.0 more polar more “ionic character”

Place these molecules in order of increasing bond polarity which is least and which is most? HCl CH 4 CO 2 NH 3 N 2 HF a.k.a. “ionic character”

non-polar MOLECULES Sometimes the bonds within a molecule are polar and yet the molecule is non-polar because its shape is symmetrical. H H HHC Draw Lewis dot first and see if equal on all sides

Polar molecules (a.k.a. Dipoles) Not equal on all sides –Polar bond between 2 atoms makes a polar molecule –asymmetrical shape of molecule

HCl -- ++

H Space filling model “Electron-Cloud” model -- ++

HH O -- ++ Water is asymmetrical ++

Water is a bent molecule O H H HH

W - A - T - E - R as bent as it can be! Water’s polar MOLECULE! The H is positive The O is not - not - not - not

Making sense of the polar non-polar thing BONDS Non-polar Polar Identical Different MOLECULES Non-polar Polar Symmetrical Asymmetrical

IONIC bonds …. Ionic bonds are so polar that the electrons are not shared but transferred between atoms forming ions!!!!!!

C. Johannesson VSEPR Theory Valence Shell Electron Pair Repulsion Theory Electron pairs orient themselves in order to minimize repulsive forces.

C. Johannesson VSEPR Theory Types of e - Pairs –Bonding pairs - form bonds –Lone pairs - nonbonding e - Lone pairs repel more strongly than bonding pairs!!!

4 Shapes of molecules

1. Linear (straight line) Ball and stick model Space filling model

2. Bent Ball and stick model Space filling model

3.Trigonal pyramid Ball and stick model Space filling model

4.Tetrahedral Ball and stick model Space filling model

Attractions between molecules –van der Waals forces Weak attractive forces between non-polar molecules –Hydrogen “bonding” Strong attraction between special polar molecules Intermolecular attractions

van der Waals Non-polar molecules can exist in liquid and solid phases because van der Waals forces keep the molecules attracted to each other Exist between CO 2, CH 4, CCl 4, CF 4, diatomics and monoatomics

van der Waals periodicity increase with molecular mass. increase with closer distance between molecules –Decreases when particles are farther away

Hydrogen “Bonding” Strong polar attraction –Like magnets Occurs ONLY between H of one molecule and N, O, F of another H “bond”

H is shared between 2 atoms of OXYGEN or 2 atoms of NITROGEN or 2 atoms of FLUORINE Of 2 different molecules

Why does H “bonding” occur? Nitrogen, Oxygen and Fluorine –small atoms with strong nuclear charges powerful atoms –very high electronegativities

Intermolecular forces dictate chemical properties Strong intermolecular forces cause high b.p., m.p. and slow evaporation (low vapor pressure) of a substance.

Which substance has the highest boiling point? HF NH 3 H 2 O WHY? Fluorine has the highest e-neg, SO HF will experience the strongest H bonding and  needs the most energy to weaken the i.m.f. and boil

The End