Structure and Bonding Flashcards
How is the quantum theory of atomic
structure differs from the Bohr’s theory?
The quantum theory explains that electrons
are in 3-dimensional shaped electron clouds that
represent the probability of an electron’s
location. Bohr’s theory explains that the
electrons are in orbits or shells.
What is the difference between an
orbit and an orbital?
Orbit is the idea of an electron “orbiting” the
nucleus like planets orbiting the sun. Orbitals are electron clouds that represent the shape of probability for an electron’s location.
What do electron configurations tell us
about the atom?
It tells about the detailed location of
electrons in an atom, the specific electron
orbitals that the electrons are found.
How many orbitals are in the fourth
energy level?
The 4th level contains s, p, d, and f orbitals,
so the total number of orbitals is 16.
How many orbitals of each type are
there? For s, p, d, and f?
s – 1
p – 3
d – 5
f - 7
______ of more than 30 million chemical compounds contain carbon.
90%
Origins of Organic Chemistry, Why is it so special?
Carbon is group 4A element, it can share 4 valence electrons and form 4
covalent bonds.
Who is often credited as
the father of modern
atomic theory?
John Dalton
Postulates by john Dalton
- Indivisibility of atom (WRONG)
- All atoms of the same element are
identical (WRONG; isotopes) - Different elements have very different
types of atoms or differ in all respects
(WRONG; isobars)
Who proposed the
planetary model of the
atom?
Niels Bohr
Planetary Model of the Atom, Main point
- Electrons orbit the nucleus in
orbits that have a set size and
energy. (WRONG) - The energy of the orbit is
related to its size. - Radiation is absorbed or
emitted when an electron moves
from one orbit to another.
It states that there is an inherent
uncertainty in the act of measuring a
variable of a particle.
Heisenberg Uncertainty Principle
Originally, electrons were thought to orbit around the nucleus in defined paths
Electron orbit model
It was discovered that electrons move in waves in a defined space called an electron cloud
Electron cloud model
Structure of an atom: small diameter
(2 X 10-10 m = 200 pm)
very dense; contains protons and neutrons
Nucleus
Diameter of nucleus
small (10-15 m)
located in space remindful of a cloud (10-10 m) around nucleus
Electrons
number of protons in nucleus
The atomic number (Z):
number of protons plus neutrons
The mass number (A):
All atoms of same element have the same
Z value
atoms of the same element with different
numbers of neutrons and thus different A.
Isotopes:
(atomic weight) of an
element is weighted average mass in atomic
mass units (amu) of an element’s naturally
occurring isotopes.
atomic mass
There are four different kinds of orbitals for
electrons based on those derived for a hydrogen
atom
▪ Denoted
s, p, d, and f
spherical, nucleus at center
s orbitals:
dumbbell-shaped, nucleus at middle
p orbitals:
elongated dumbbell-shaped, nucleus
at center
d orbitals:
tetrahedral, nucleus at center
f orbitals:
Orbitals are grouped in ______ of increasing size and energy
shells
Each orbital can be occupied by ____________
two electrons.
Third shell contains an s orbital (3s), three p orbitals (3p),
and five d orbitals (3d), holds ______ electron
18
Second shell contains one s orbital (2s) and three p orbitals
(2p), holds _____ electrons
eight
Lobes of a p orbital are separated by region of zero electron
density,
node.
(i.e., lowest energy arrangement) of an atom
▪ lists orbitals occupied by its electrons.
Ground-state electron configuration
Rules ground-state electron configuration
- Lowest-energy orbitals fill first:
- Electrons act as if they were spinning around an axis.
Electron spin can have only two orientations, up and down
. Only two electrons can occupy an orbital, and they must
be of opposite spin - If two or more empty orbitals of equal energy are
available, electrons occupy each with spins parallel until
all orbitals have one electron
Principle in 1. Lowest-energy orbitals fill first:
(Aufbau (“build-up”) principle)
Principle in Electrons act as if they were spinning around an axis.
Electron spin can have only two orientations, up and down
. Only two electrons can occupy an orbital, and they must
be of opposite spin
(Pauli exclusion principle)
Principle: 3. If two or more empty orbitals of equal energy are
available, electrons occupy each with spins parallel until
all orbitals have one electron
(Hund’s rule).
Atoms form bonds because
the resulting compound is more
stable than the separate atoms
Ionic bonds in salts form by
electron transfers
(electron dot) show valence electrons of
an atom as dots
Lewis structures
have a line drawn
between two atoms indicating a 2 e- covalent bond.
Kekulé structures
Stable molecule results at completed shell,
octet (eight dots)
for main-group atoms (two for hydrogen)
Atoms with one, two, or three valence electrons form
one,
two, or three bonds, respectively.
Atoms with four or more valence electrons form as many
bonds as electrons needed to fill the s and p levels of their
valence shells to reach a _____________
stable octet.
Carbon has four valence electrons (2s
2 2p
2
), forming ________
four bonds
Valence electrons not used in bonding are called
nonbonding electrons, or lone-pair electrons
forms when two atoms approach each other
closely so that a singly occupied orbital on one atom
overlaps a singly occupied orbital on the other atom
Covalent bond
Two models to describe covalent bonding:
▪ Valence bond theory
▪ Molecular orbital theory
Electrons are paired in the overlapping orbitals and are
attracted to nuclei of both atoms
▪ H–H bond results from the overlap of two singly occupied
hydrogen 1s orbitals
Valence Bond Theory:
H-H bond is cylindrically symmetrical,
sigma (s) bond
H–H has bond strength of
436 kJ/mol
is a factor
that leads to
maximum or
minimum stability.
Distance between
nuclei
If too close, they
repel because both
are
positively
charged
If too far apart,
bonding is
weak
independently observed that carbon
always has four bonds
Kekulé and Couper
proposed that the four bonds of
carbon have specific spatial directions
van’t Hoff and Le Bel
sp3 hybrid orbitals: an s orbital and three p orbitals combine to form four
equivalent, unsymmetrical, tetrahedral
orbitals
C–H bond has a strength of ______ and a length of _____ pm
439 kJ/mol and 109 pm
The remaining p orbital in sp2 is
perpendicular to the plane
Two sp2
-hybridized
orbitals overlap to form a
s bond.
Two sp2
-hybridized
orbitals overlap to form a
sigma
bond
Electrons in the s bond are
centered between nuclei
Electrons in the sigma bond
occupy regions are on either side
of a line between nuclei
Ethylene C=C bond length ____
134 pm
sp orbital placement of tow p-orbitals
perpendicular to the y and z axis
H–N–H bond angle in ammonia
(NH3)
107.3°
C-N-H bond angle is
110.3 °
where electrons are most likely
to be found (specific energy and general shape) in a molecule
molecular orbital
MO is lower in energy
Additive combination
MO is higher in
energy
Subtractive combination
is from combining p orbital lobes with
the same algebraic sign
The additive bonding MO
is from combining lobes with
opposite signs
The antibonding MO
don’t
have C-H or C-C single
bonds shown. They are
understood.
Condensed structures
Drawing Skeletal Structures
(Commonly Used)
1) Carbon atoms
aren’t usually
shown
2) A carbon atom is assumed to be at each intersection of
two lines (bonds) and at the end of each line.
3) Hydrogen atoms bonded to carbon aren’t shown.
4) Atoms other than carbon and hydrogen ARE shown
Electrons occupy ______ around the nucleus.
orbitals
