Octet rule
The tendency of atoms to gain, lose or share electrons to obtain 8 electrons in their valence shells (representative elements)
Valence shell
outermost shell of electrons in an atom.
Ion
an electrically charged atom or group of atoms.
(positive or negative)
Form octets:
~To become more stable
~By losing, gaining, or sharing electrons.
~By forming ionic bonds or covalent bonds.
Cation
a positively charged ion formed by the loss of one or more electrons.
(metals)
Name: Element name and the word ion.
[Ex. Na+ is Sodium ion, Ca+2 is Calcium ion]
Anion
A negatively charged ion, formed by the gain of one or more electrons.
(nonmetals)
Name: Change suffix to -ide and the word ion.
[Ex. Cl- is Chloride ion, O2- is Oxide ion]
Metals
Form positive ions (cations) / achieve octet:
~By losing valence electrons.
~That form positive ions with the number of electrons of the nearest noble gas.
~That have fewer electrons than protons.
Ex. group 1A --> ion 1+
group 2A --> ion 2+
Group 3A --> i
Group 1A (Alkali Earth Metals)
(ionic charge)
lose 1 electron to form ions with a 1+ charge
(group number = charge)
Group 2A (Alkaline earth metals)
(ionic charge)
lose 2 electrons to form ions with a 2+ charge.
(group # = charge)
Group 3A
(ionic charge)
lose 3 electrons fto form ions with a 3+ charge.
(group # = charge)
Nonmetals
Form negative ions (anions) / achieve octet:
~By gaining electrons
~With charges of 1-, 2- or 3-
Group 5A
(ionic charge)
Gains 3 electrons to form an ion with a 3- charge.
(only nonmetals above metalloid line)
Group 6A
gains 2 electrons to form and ion with a 2- charge.
(only nonmetals above metalloid line)
Group 7A (Halogens)
(ionic charge)
Gains 1 electron to form an ion with a 1- charge.
(only nonmetals above metalloid line)
Group 8A (Noble gases)
Do not gain or lose electrons since they already have 8 electrons in their valence shell.
Group 4A
don't make ions.
They will share electrons rather than gain or lose them.
Ionic Compounds
Consist of positive and negative ions.
Usually crystalline solids.
Conduct electricity when dissolved in water.
Have high melting points & boiling points.
Water soluble (only if attraction of the water for the ion overcomes the attraction of the ions for
Ionic formula
Indicates the number and kinds of ions that make up the compound.
The number of positive charges must equal the negative charges.
Sum of all charges is always zero.
Metal first, nonmetal second.
[Ex. NaCl, MgCl2, Na2S]
Transition elements (and group 4A metals)
Variable charge
Form 2 or more kinds of positive ions. (exception: Zn 2+, Ag+, Cd 2+)
Cannot use group # to determine ionic charge.
[Ex. Fe 2+, Fe 3+]
Name: Use Roman Numerals to indicate the charge of the ion.
[Ex. Fe 2+ is Iron (II), Fe 3+ is Iron (III)
How to assign chg to Transitional metals
1. Determine the charge of the cation from the anion
2. Name the cation by it's element name and (Roman numeral) for the charge.
3. Name the anion (change end to -ide)
4. Write name of Cation first & Anion second.
Ex.
FeCl2, Iron (II) chloride
FeCl3, Iron
How to write ionic formulas from name
!. Identify cation and anion.
2. Balance the charges.
3. Write the formula, cation first, using subscripts from the charge balance.
Ex.
Cromium (III) oxide, Cr2O3 (because oxygen has 2- chg)
Iron (II) chloride, FeCl2 (
Polyatomic ions
Ions that are composed of more than one atom.
The atoms are held together by covalent bonds and the entire group of atoms acts as a single unit.
Charge because the total # of electrons is different than the total number of protons for the whole group, res
Polyatomic ions (naming)
end in -ate
Ex. PO4 3-, Phosphate, NO3 -, Nitrate
With one less oxygen, end in -ite
Ex. PO3 3-, Phosphite, NO2 -, Nitrite
With Hydrogen, use Hydrogen or Bi-
Ex. HCO3 -, Hydrogen carbonate or bicarbonate
HSO3 -, hydrogen sulfite or bisulfite
exceptions:
Hy
Covalent bonds
A bond formed by sharing electrons between atoms of 2 nonmetals.
Electrons are shared, not transferred.
Forms:
~When atoms share electrons to complete octets.
~Between two nonmetal atoms.
~Between nonmetal atoms from Groups 4A, 5A, 6A, 7A.
Molecule
A group of atoms held together by covalent bonds.
Multiple covalent bonds
Single bond - bond formed by sharing 1 electron pair.
C-C
Double bond - bond formed by sharing 2 electron pairs.
C=C
Triple bond - bond formed by sharing 3 electron pairs.
Most common multiple bond elements:
C, N, O, S
Properties of covalent molecules
Low melting points & boiling points.
Can be gases, liquids or solids at room temp.
Not soluble in water.
Do not conduct electricity when dissolved in water.
Naming covalent compounds
1. Name first nonmetal as element.
2. Name second nonmetal with -ide ending.
3. Use prefixes to indicate number of atoms (subscript) of each element.
ex. SiBr4, Silicon tetrabromide
Br2O, Dibromine oxide.
Prefixes for covalent compounds
1) Mono
2) Di
3) Tri
4) Tetra
5) Penta
6) Hexa
7) Hepta
8) Octa
9) Nona
10) Deca
Electronegativity
The attraction of an atom for valence electrons in a chemical bond.
Nonmetals have higher electronegativity values because they have greater attraction for electrons than metals.
Electronegativity value
Indicates the attraction of an atom for shared electrons.
Increases from left to right.
High for nonmetals (flourine highest)
Low for metals.
(works the same way for ionization energy - transferring electrons)
Types of bonds
Nonpolar covalent bond: electrons shared equally
Polar covalent bond: electrons shared unequally (dipole)
Ionic bond: Electrons transferred.
Nonpolar covalent bond
Shared Equally
Occurs between nonmetals.
An equal (or almost) sharing of electrons
Has almost no electronegativity difference (0.0 - 0.4)
Polar covalent bond
Shared unequally
Occurs between nonmetal atoms
An unequal sharing of electrons.
Has moderate electronegativity difference (0.5 - 1.7)
Atoms in a covalent bond have different electronegativity values. The electrons are attracted to the more electronegative
Dipole
The separation of charges in a polar covalent bond.
(2 poles identified by Greek symbol delta)
Ionic bond
The electrical attactions between ions of opposite charges.
Composed of cation (+ chg, metal) and anion (- chg, nonmetal).
Occurs between metal and nonmetal.
A result of electron transfer.
Has a large electronegativity difference (1.8 or more)
Naming simple compounds
Transitional elements that form only one ion
Zinc, Zn 2+
Silver, Ag +
Cadmium, Cd 2+
Most common multiple bond elements
Carbon, C
Nitrogen, N
Oxygen, O
Sulfur, S