Chemical BondingMs. Manning

Back to Compounds….. 2 Types:

Covalent CompoundsFormed when non-metals bond with

other non-metals Ionic Compounds

Formed when metals bond with non-metals

Classification

Compound of:

Bonding

Structure

Tm and Tb

Conductivity in Solid

Conductivity in Liquid

Metals Metallic Lattice High High High

Metals and Non Metals

Ionic Lattice High Low High

Non Metals

Covalent

Lattice High Low Low

Non Metals

Covalent

Molecular

Low Low Low

Properties of Metallic compounds

Relatively dense solids (exception Hg)

Good conductors of heat and electricity

Lustrous when clean/ freshly cut Strong, malleable (can be

shaped) and ductile (can be drawn into a wire)

Sonorous: Ringing sound when hit

Relatively high melting and boiling points

Usually form positive ions

Properties of Non-Metals Non-lustrous Can exist in any state -

generally gases at room temperature

Brittle, non-ductile Poor conductors of heat and

electricity Usually exist as molecules in

their elemental form Low densities, melting and

boiling points. Combine with other nonmetals

to form covalent bonds Generally form negative ions,

e.g.  Cl-, SO42-, and N3-

Properties of Metalloids Generally look metallic but are brittle (not

malleable or ductile) Neither good conductors or insulators;

instead they are semiconductors.

Chemical BondingChemical Bond = the force of attraction holding atoms or ions together

This is how compounds are made!

Classifying CompoundsIonic Compound = a pure substance formed from a metal and a nonmetal NaCl CaO

Molecular Compound = a pure substance formed from two or more different nonmetals SO2

CO2

Ionic versus Molecular CompoundElectrical Conductivity = the ability of a material to allow electricity to flow through it

Ionic Compounds conduct electricity

Molecular Compounds DO NOT

ElectrolyteElectrolyte = a substance that forms a solution that conducts electricity

Ionic compounds form electrolytic solutions

Molecular compounds form non-electrolytic solutions

Ionic BondingIons = atoms that have gained or lost electrons

Ionic Bond = the electrostatic attraction between positive and negative ions in a compound Metals lose electrons Non-metals gain electrons Both form octets = MORE STABLE

Ionic Bonding – Bohr Diagrams

Lewis Dot Diagrams – Ionic Bonding

MgCl2

KBr

Naming Ionic Bonding Ionic Compounds

Metal + Non-metal Metal name same as on the atom

name Non-Metal suffix “-ide” Example:

NaCl = Sodium ChlorideLiF = Lithium FlourideMgO = Magnesium Oxide

Non-metal Suffixes Nitrogen = Nitride Oxygen = Oxide Fluorine = Fluoride Phosphorus = Phosphide Sulfur = Sulfide Chlorine = Chloride Selenium = Selenide Bromine = Bromide Iodine = Iodide

How Many Atoms in a Molecule?Diatomic Molecules = a molecule consisting of two atoms of the same or different elements CO

Polyatomic Molecules = a molecule consisting of more than two atoms of the same or different elements NH3

Covalent BondingCovalent Bond = the attractive forces between two atoms that results when electrons are shared by the atoms A simultaneous attraction of two nuclei

for a shared pair of electrons

In Lewis Diagrams – the shared pairs of electrons are shown as lines and the lone pairs as dots

Octet Rule Still Applies!The shared pair of electrons is considered to be a pair of electrons that make both atoms have an octet

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Lewis Dot Diagrams – Covalent Bonds

The Lone PairLone Pair = a pair of valence electrons not involved in bonding

Bonding CapacityBonding Capacity = the number of electrons lost, gained or shared by an atom when it bonds chemically Allows us to predict how many bonds an

atom can form

Bonding CapacityAtom # of

Valence Electrons

Number of Bonding Electrons

Bonding Capacity

Carbon 4 4 4

Nitrogen 5 3 3

Oxygen 6 2 2

Halogens 7 1 1

Hydrogen 1 1 1

Choosing the Central Atom for Polyatomic MoleculesThe central position…

Is usually occupied by the element with the highest bonding capacityC and N are often in the central position

The least electronegative atom is usually the central atom

Hydrogen is NEVER the central atom Oxygen and Halogens are usually not

the central atom

Covalent Bonds = StrongA large amount of energy is needed to separate the atoms that make up molecules

The stronger the bond the greater the amount of energy needed to break the bond Single bond = strong Double bond = stronger Triple bond = strongest

Single, Double & Triple Bonds

Polar Covalent BondsPolar Covalent Bonds = a covalent bond formed between atoms with significantly different electronegativities; a bond with some ionic characteristics When electrons are shared between two

atoms = covalent bond In a bond between identical atoms the electrons

are shared equally In a bond between two different atoms the

sharing is unequal

Non-Polar versus Polar Covalent

Comparison…

Difference in Electronegativity…

If the electronegativity difference is: less than 0.2 = bond is pure covalent is between 0.2 and 1.6 = bond is polar covalent

is greater than 1.7 = bond is ionic

Polar MoleculesPolar Molecules = a molecule that is slightly positively charges at one end and slightly negatively charged at the other because of electronegativity differences

Types of ForcesIntramolecular Force = the attractive forces between atoms and ions within a compound Ionic Polar Covalent Non-polar Covalent

Intermolecular Force = the attractive force between molecules

IntRA versus IntER-molecular Forces

Some Intermolecular Forces3 major types of Intermolecular Forces: Dipole-dipole forces London dispersion forces Hydrogen bonding

The first two are known as van der Waals Forces London dispersion forces and dipole-

dipole forces

van der Waals Force Dipole-dipole force = an attractive force acting between polar molecules Attraction between oppositely charged

ends of polar molecules

van der Waals Force London Dispersion force = an attractive force acting between all molecules including nonpolar molecules A result of temporary

displacements of the electron “cloud” around the atoms in a molecule resulting in a extremely short-lived dipole

London Dispersion Force

Hydrogen BondingHydrogen Bonding = a relatively strong dipole-dipole force between a positive hydrogen atom of one molecule and a highly elecgtronegative atom (F, O or N) in another molecule

Hydrogen Bonding

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