Chem Unit 3

octet rule

octet rule

all elements seek to have 8 valence electrons

how do atoms bond?

through transfer or share of the valence electrons

ionic bonding

• creates electrostatic attraction or force

• brings both anions and cations together

ionic bonding 2

• transfer of valence electrons

• creates electrostatic attraction or force that brings both ions together

ionic bonding 3

between a metal and nonmetal or includes a poly-atomic ion

poly-atomic ion

• also known as a molecular ion

• a group of atoms bonded together with a charge

ternary compounds

compounds with 3 or more elements, usually one being a poly-atomic ion

metals

lose electrons and become cations

nonmetals

gain electrons and become anions

charges & oxidation numbers

charges are also called oxidation numbers

“crisscross charges trick” for ionic formulas RULES

• compounds must be NEUTRAL

• if you do crisscross, charges become subscripts!

“crisscross charges trick” for ionic formulas examples

basic ionic nomenclature (naming)

• ALWAYS 2 words = METAL name 1st, Nonmental name 2nd

• Metals = names are found on the Periodic Table (ex: Na is Sodium)

• Nonmetals = use the root name on Periodic Table and end it with “ide” (ex: Fluoride - “fluor” is the root word)

special names for nonmetals

• phosphorus: phosphoride

• sulfur: sulfide

• iodine: iodide

• nitrogen: nitride

• oxygen: oxide

special ionic compounds - transition metals

• must add roman numerals to indicate the charge the metal name

• multiple oxidation state - more than 1 charge

• metal name - from PT

• oxidation #’s (or charges) vary

certain charges

• Ag^+ = Ag always has a +1 charge

• Zn²^+ = Zinc will always have a +2 charge

polyatomic ions w/ metals

Name metal FIRST, poly-atomic ion SECOND

how do you know if its a binary or ternary bond?

the amount of elements tells you

properties of ionic compounds

• known as salts

• crystal lattice structure

• rarely burn

• hard and brittle

• conduct electricity when dissolved in water

• high melting & boiling points

covalent bonds

• between 2 nonmetals

• bond is formed through the sharing of valence electrons

• To be stable, compounds want to have 8 ve^- (valence electrons)

what is a covalent compound also referred to as?

a molecule

How many valence electrons does hydrogen need to be stable? (covalent bonding)

H only needs 2 valence electrons to be stable

single bonds

1 pair of electrons, so 2 total electrons

double bonds

2 pairs of electrons, so 4 total electrons

triple bonds

3 pairs of electrons, so 6 total electrons

facts about the 3 types of bonds

• hydrogen & halogens (GROUP 17) usually form single bonds

• GROUP 16 elements usually form double bonds

• GROUP 15 elements usually form triple bonds

which type of bond does Hydrogen never form?

double bonds

what types of bonds can Carbon form?

carbon can form all types of bonds and typically has 4 total electrons!

HONC Rule (made-up mnemonic)

Hydrogen, Oxygen, Nitrogen, Carbon

covalent nomenclature

• NONMETALS ONLY!

• name from the PT of the 1st symbol in formula is always written 1st! It’s usually carbon and NEVER hydrogen.

• name from the PT of the 2nd symbol in formula is written next. Use the root of the name and add the ending ide.

• look at subscripts and determine the # of atoms and add any prefixes.

• If only 1 atom of the first symbol, you don’t write down mono.

covalent nomenclature prefixes

• mono: 1

• di: 2

• tri: 3

• tetra: 4

• penta: 5

• hexa: 6

• hepta: 7

• octa: 8

• nona: 9

• deca: 10

water covalent nomenclature

dihydrogen monoxide

hydrogen gas covalent nomenclature

(H2) dihydrogen

acidic compounds & acidic nomenclature

• H is ALWAYS written FIRST!!!

• No oxygen in compound (binary)

• oxygen in compound (ternary)

H₃P

Hydrophosphoric Acid

HSe

Hydroselenic Acid

Chlorous Acid

HCl0₂

H₂CO₃

Carbonic Acid

Lewis Dot Structures Rules

• FIND THE CENTRAL ATOM (usually the 1st atom (or symbol) in formula; IT CAN NEVER BE HYDROGEN)

• ARRANGE OTHER ATOMS AROUND CENTRAL ATOM!

• MAKE ATOMS STABLE! DRAW 8 ELECTRONS AROUND EACH. (ONLY 2 ELECTRONS FOR HYDROGEN!)

• COUNT THE TOTAL # OF ELECTRONS AND COMPARE TO # OF VALENCE ELECTRONS

  • if valence electrons are shared equally = single bonds

  • if valence electrons are NOT shared equally = remove electrons from central atom

• REARRANGE YOUR PICTURE W/ BONDS!

Which compounds ONLY can you draw Lewis Dot Structures for?

Covalent Compounds!

Atoms w/ an expanded octet

PCl₅

Atoms w/ a reduced octet

BH₃

resonance structures

• when more than one Lewis Structure is valid

• only found in molecules w/ double or triple bonds.

• includes average of all the bonds

molecular geometry

• shape of molecules

• electrons want to be as far away as possible because charges repel.

• look at central atom to determine molecular geometry.

VSEPR Theory

• “Valence Shell Electron Pair Repulsion”

• Format:

  • AXE - where:

  • A: ALWAYS central atom

  • X: # of bonding areas/regions

  • E: # of lone pairs

molecular geometry steps

• draw the correct Lewis structure.

• count the bonding areas and lone pairs on the central atom

• write AXE format

• determine your geometry (the type)

• draw!

bond polarity (ionic)

Ionic:

• transfer of electrons between atoms w/ very different electronegativity values

• form salts or ionic compounds

bond polarity (covalent)

Covalent:

• sharing electrons between atoms with similar electronegativity

• form molecules or covalent compounds

dipole moments

electrons are attracted to more electronegative atoms

electronegativity polarity ranges (nonpolar)

need chart with the actual values

• less than or equal to 0.5

• 2 of the same atom

electronegativity polarity ranges (polar covalent)

need chart with the actual values

• between 0.5-1.7

• 2 different atoms

electronegativity polarity ranges (ionic)

need chart with the actual values

• between metals & nonmetals

• greater than or equal to 1.7

only nonpolar exception?

C-H

how to check for polarity in molecular geometry

look at Lewis dot structure and check for SYMMETRY

polar (polarity in molecular geometry)

• ASYMMETRIC

• look for lone pair of electrons on the central atom

• variety of atoms around the central atom

• variety of bonds between atoms

nonpolar (polarity in molecular geometry)

• PERFECTLY SYMMETRICAL

• no lone pair on central atom

• same atoms around the central atom

• same type of bonds between atoms

metallic bonding

occurs when the delocalized electrons in metal atoms are attracted to the lattice or positive metal ions.

delocalized

means that the electrons do not belong to any one metal nucleus but can spread themselves throughout the metal structure

The strength of the metallic bond depends on what?

• the number of delocalized electrons

• the size of the cation

• the charge of the cation

sodium delocalized electrons

1

magnesium delocalized electrons

2

conductivity

metals are good conductors of electricity and heat (thermal conductivity) because the delocalized electrons are highly mobile and move through the metal structure.

alloys

a material w/ metallic properties consisting of a homogeneous mixture of at least one metallic element and other either metallic or nonmetallic elements.