Unit Four Flashcards
Polyatomic ion
An ion made up of two or more atoms
PO4-3
Cation
A positive ion Forms from the loss of electrons Metals Mg2+ Li+
Anion
A negative ion Forms from the gain of electrons Nonmetals N3- S2-
Naming cations
Keep the name of their parent ion, add ion to the end
Name an ion of Mg
Magnesium ion
Naming anions
Keep the root of their name but change the ending to ide
Name a nitrogen ion
Nitride ion
Chemical bond
An attractive force between atoms or ions that binds them together as a unit
Why do bonds form?
Decrease potential energy
Increase stability
Compound
A pure substance made of two or more elements that are chemically combined
Monotmic ion
An ion made up of one atom
Na+
Molecule
A special term used to describe compounds that are made by the sharing of electrons (covalent bond)
Binary compound
A compound containing two different elements
CaF2
Ionic bonds
A bond formed from the transfer of electrons (one atom loses electrons and the other one gains them)
Often referred to as salts
What types of atoms can form ionic bonds?
Metal and a nonmetal
Metal and a polyatomic ion
Polyatomic ion and a nonmetal
Two polyatomic ions
Structure of an ionic bond
Crystal lattice
Result of positive and negative ions stacking themselves up so they will be near an ion of opposite charge
Strength of ionic bonds
Very strong because the opposite charges inside attract each other, making it hard to pull them apart
Melting and boiling point of ionic bond
High melting and boiling point because their bonds are very strong so they require a lot of energy to break
Conductivity of ionic bonds
Can conduct electricity when they are dissolved in water or molten, don’t conduct electricity when solid because the ions are locked in place and can’t allow the electrons to flow
Are ionic compounds soft?
No they are hard but very brittle—energy required to break is large, it will shatter whole structure instead of breaking just one
Covalent bond
Forms when two atoms share electrons so they can both satisfy the octet rule. Because they are sharing electrons, there is no cation or anion in a covalent molecule (no charges).
What types of atoms can form covalent bonds?
Formed between nonmetals only
Structure of covalent bonds
Structure can vary
Strength of covalent bonds
Weak—there are positive and negative ions being attracted to each other
Melting and boiling point of covalent bonds
Low melting and boiling point—weak type of bond so less energy to break them
Conductivity of covalent bonds
Don’t conduct electricity—don’t break into ions so electrons can’t flow through
Acids
First element is Hydrogen (H) can be bonded to a nonmetal or polyatomic ion
Technically an ionic bond where H gives away its one valence electron
Only exception is water
Polar covalent bond
Atoms are not equally sharing electrons (this is because one of the atoms is stronger)
Nonpolar covalent bond
Atoms are equally sharing electrons
Get partial charges
Polarity is determined by…
The electronegativity of the atoms bonded together
Electronegativty
The ability for an atom to pull shared electrons towards itself (strength)0
Difference of electronegativities is:
0.5?
_>0.5
_>1.7?
Nonpolar
Polar
Ionic
Bond length from lowest to highest
Ionic
Bond strength from lowest to highest
Nonpolar covalent
Ternary compound
A compound containing three or more different elements
Two rules for writing formulas
Cation has to come before the anion (positive comes before negative)
The charges of the ions have to cancel out, use criss cross rule
Acetate
(CH3COO)-1
(C2H3O2)-1
Ammonium
(NH4)+1
Carbonate
(CO3)-2
Cyanide
(CN)-1
Hydroxide
(OH)-1
Phosphate
(PO4)-3
Phosphite
(PO3)-3
Nitrate
(NO3)-1
Nitrite
(NO2)-1
Sulfate
(SO4)-2
Sulfite
(SO3)-2
For ionic compounds, what do you do?
Leave the first ion normal and change the ending of the second one to ide
Naming formulas with polyatomic ions
Normal—put the positive one in front and negative in back, keep names of both, except if normal ion is in back, then change its ending to ide
What is always the charge on silver?
Ag+
What is always the charge on zinc?
Zn+2
What is always the charge on cadmium?
Cd+2
What is always the charge on aluminum?
Al+3
What is always the charge on gallium?
Ga+3
What is the number in Roman numerals in naming transition metals?
The charge of an atom
Naming covalent molecules
Add a prefix if they have a prefix
If there is only one of the second element, add mono (but not if there is only one of the first element)
The second element ends in ide
Oxygen drops some of the prefix endings
Prefix for 1
Mono
2
Di
3
Tri
4
Tetra
5
Penta
6
Hexa
7
Hepta
8
Octa
9
Nona
10
Deca
Naming acids that don’t have oxygen
Add prefix hydro and suffix ic to the anion
Add acid after that
Naming acids with oxygen
If it ends in ate, change to ic
If it ends in ite, change it to ous
Add acid
Exceptions for acids
Phosphorus without oxygen: Phosphoric Sulfur without oxygen: Sulfuric Phosphate: Phosphoric Phosphite: Phosphorous Sulfate: Sulfuric Sulfite: Sulfurous
Lewis dot structures
Show the number of valence electrons for a given atom
Octet rule
Atoms will gain, lose, or share atoms in order to have a full valence shell
How to draw a Lewis dot structure for an atom
Each atom is represented by its symbol
No more than two electrons may go on each side of the atom
Only valence electrons appear in Lewis dot structures
How to draw a Lewis dot structure for a compound
Each bond represents two electrons being shared between two atoms
- Count the total number of valence electrons for all atoms in the compound
- Draw a single bond from the central atom to each of the attached atoms. The central atom is typically the atom written first in a chemical formula
- Complete each outer atoms octet first
- Put any extra electrons on the central atom
- If your central atom did not obtain a stable octet with the previous step, you must create multiple bonds to satisfy the octet rule for all atoms
Single bond is…
Double bond is…
Triple bond is…
2 electrons
4 electrons
6 electrons
Bond length
Bond strength
Length decreases with an increased number of bonds
Strength increases as you increase the number of bonds
Multiple bonds are common between
Carbon, nitrogen, oxygen, and sulfur
How many electrons does hydrogen need to have a full valence shell?
2
How many electrons does boron need to be stable?
Only 6
The central atom forms…
The most bonds—it is usually the element that you only have one of, but not always
Draw some Lewis dot structures for practice
Hopefully you got them right
Polyatomic ion
Multiple ions bonded together
What do you do if the compound has a charge?
Add or subtract electrons to the total depending on the charge
Polyatomic ion Lewis dot structures
Same thing but put the charge into the total number of electrons and put it in brackets and put the charge outside the brackets
What does VSEPR stand for?
Valence shell electron pair repulsion (theory)
VSEPR theory
The negative charges on electrons causes them to repel each other. As a result, the atoms in a molecule try to spread out as far as possible.
Shapes are determined by the repulsion forces between shared and unshared electron pairs.
Before determining a shape, you must draw the Lewis dot structure.
MXE formulas
M = middle or central atom X = attached atoms E = lone electron PAIRS on the central atom
MX2 whole thing
Example = CO2 Draw Lewis dot structure Molecular geometry (shape) =linear Polarity = nonpolar (as long as all attached atoms are the same element) Bond angle = 180°
MX3 whole thing
Example = BH3 Draw Lewis dot structure Molecular geometry (shape) = trigonal planar Polarity = nonpolar (as long as all attached atoms are the same) Bond angle = 120°
MX4 whole thing
Example = CH4 Draw Lewis dot structure Molecular geometry (shape) = tetrahedral Polarity = nonpolar (as long as all attached atoms are the same) Bond angle = 109.5°
MX2E whole thing
Example = SO2 Draw Lewis dot structure Molecular geometry (shape) = bent Polarity = polar Bond angle = n/a
MX2E2 whole thing
Example = H2O Draw Lewis dot structure Molecular geometry (shape) = bent Polarity = polar Bond angle = n/a
MX3E whole thing
Example = NH3 Draw Lewis dot structure Molecular geometry (shape) = trigonal pyramid Polarity = polar Bond angle = n/a