Upload
whitney-harper
View
217
Download
0
Tags:
Embed Size (px)
Citation preview
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
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
88
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
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
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
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
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