Chapter 5 - Chemical Bonding Flashcards
How do you name molecular compounds?
Greek prefix to shown no. of atoms in first element
Name of first element
Greek prefix to show no. of atoms in second element
add ‘ide’ to second element
What is the Greek prefix for 1?
mono
What is the Greek prefix for 2?
di
What is the Greek prefix for 3?
tri
What is the Greek prefix for 4?
tetra
What is the Greek prefix for 5?
penta
What is the Greek prefix for 6?
hexa
What is the Greek prefix for 7?
hepta
What is the Greek prefix for 8?
octa
What is the Greek prefix for 9?
nona
What is the Greek prefix for 10?
deca
What is H2O?
Water
What is N2H4?
Hydrazine
What is H2O2?
hydrogen peroxide
What is NH3?
Ammonia
What is C2H2?
Acetylene
What is PH3?
Phosphine
What is AsH3?
Arsine
What is NO?
Nitric oxide
What is N2O?
Nitrous Oxide
What is CH4?
Methane
When do Covalent bonds form?
when valence electrons are shared to provide each atom with a full octet
What are electrons shared by covalently bonding called?
bonding electrons
How do you draw more complex covalent bonds?
- adding up of all the valence electrons
- pick a central atom, arrange other atoms around central atom, connect w/ single bond
- fill the octets of outer atoms, left over electrons fill octet of central atom
- if octets aren’t filled try multiple bonds
What does the Lewis model account for?
Why particular combinations of atoms form molecules and others do not
Hydrogen and the halogens are all diatomic molecular elements
oxygen generally forms either 2 single bonds or a double bond in its molecular compounds
What are the Lewis Models limitations?
bonding electrons depicted as typically shared between atoms (often not the case)
What is electronegativity?
the ability of an atom to attract bonding electrons to itself increases across period (left to right) and decreases down group (top to bottom) The larger the difference in electronegativity, the more polar the bond
What does electronegativity values go from?
0.7 to 4.0
What is lowest electronegativity?
0.7 Francium
What is the highest electronegativity?
4.0 Fluorine
In polar covalent bonds the end with more electron density gets a what?
partial negative charge (and vice versa)
Electronegativity of 0-0.4 is what type of bond?
covalent
Electronegativity of 0.4-2.0 is what type of bond?
Polar Covalent
Electronegativity of 2.0+ is what type of bond?
Ionic
What are resonance results?
when we can draw more than one Lewis Structure
What is a resonance hybrid?
intermediate between multiple resonance structures; average of the possible Lewis Structures
What is formal charge?
fictitious charge assigned to each atom in a Lewis Structure if all bonding electrons were shared equally
results from a kind of electron ‘bookkeeping’
What is the goal of formal charge calculation?
sum of formal charges in neutral molecule must be zero
sum of formal charges in ion must equal charge of ion
every atom should have a formal charge of 0 if possible
negative charge if any should be on most electronegative atom
How do you calculate formal charge?
no. of valence electrons - (no. of non bonding electrons + 1/2 of bonding electrons)
What are the 3 exceptions to the Octet rule?
Odd-Electron species
Incomplete Octets
Expanded Octets
What is an Odd-Electron Species?
odd number of electrons, can’t satisfy all octets
- free radicals
-unstable
-few in number
(e.g. NO)
What are Incomplete Octets?
Where due to bonding preferences, octets are not full
(e.g. BF3 as Boron likes to have only 3 bonds)
What are Expanded Octets?
Where central atom has greater number of electrons than an octet
can only occur in third row and beyond as they can access d orbitals
What is Bond Energy?
Energy required to break one mole of the bond in the gas phase
What is the relationship between bond length and energy?
in general as length increases, the bond gets weaker, trend doesn’t always apply for similar compounds/ different compounds
