Chemical BONDING

electron shells Atomic number = number of Electrons Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells. Electron shells determine how an atom behaves when it encounters other atoms

Electrons are placed in shells according to rules: The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like to N would like to O would like to Gain 4 electrons Gain 3 electrons Gain 2 electrons

Why are electrons important? Elements have different electron configurations different electron configurations mean different levels of 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

What did the atom of fluorine say to the atom of sodium? You complete me.

Bond Formation exothermic process ENERGY Reactants Energy released Products

Breaking Bonds Endothermic reaction energy must be put into the bond in order to break it ENERGY Products Energy Absorbed Reactants

Bond Strength Strong, STABLE bonds require lots of energy to be formed or broken weak bonds require little E

Is a bond forming or breaking? Strong or weak bond? Reaction Time Energy (KJ) energy absorbed endothermic bond breaking weak unstable bond Products Reactants

Is a bond forming or breaking? Strong or weak bond? Reaction Time Energy Energy absorbed endothermic bond breaking strong stable bond Products Reactants

Is a bond forming or breaking? Strong or weak bond? Energy (KJ) Reaction Time Energy released exothermic bond formation weak unstable bond Reactants Products

Is a bond forming or breaking? Strong or weak bond? Energy (KJ) Reaction Time Reactants Products Energy released exothermic bond formation strong stable bond

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 me-tals to conduct electricity!!!!!!

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

[METALS ]+ [NON-METALS ]- 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 CaCl2 Compounds with polyatomic ions NaNO3

Anion (-) Cation (+)

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

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

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

Covalent, Ionic, metallic bonding? NO2 sodium hydride Hg H2S sulfate NH4+ 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-

[Na]+ [ Cl ]- NaCl This is the finished Lewis Dot Structure 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 lewis dot structure for each atom. - Draw an arrow from the electrons that move to where they move. Step 3 Write the symbol for the + ion first. NO DOTS Draw the e- dot diagram for the – ion COMPLETE outer shell Step 4 Enclose both in brackets and show each charge

Draw the Lewis Diagrams LiF MgO CaCl2 K2S

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 CH4 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”. Cl2 Br2 H2 O2 N2 HCl

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

Draw Lewis Dot Structures You may represent valence electrons from different atoms with the following symbols x, , CO2 NH3

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

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 CH4 CO2 NH3 N2 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 C 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

H Cl + -

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

Water is asymmetrical + + H O -

Water is a bent molecule H H

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!!!!!!

4 Shapes of molecules

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

Bent Ball and stick model Space filling model

Trigonal pyramid Ball and stick model Space filling model

Tetrahedral Ball and stick model Space filling model

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

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 CO2, CH4, CCl4, CF4, diatomics and monoatomics

van der Waals periodicity increase with molecular mass. Greater van der Waals force? F2 Cl2 Br2 I2 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”

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 NH3 H2O 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 Unusual Properties of Water Unusually high boiling point Compared to other compounds in Group 16

Density????

H2O(s) is less dense than H2O(l) The hydrogen bonding in water(l) molecules is random. The molecules are closely packed. The hydrogen bonding in water(s) molecules has a specific open lattice pattern. The molecules are farther apart.

The End