Transcript ATOMIC STRUCTURE Chapter 7

Ch 4 Arrangement of Electrons
in atoms
ELECTROMAGNETIC RADIATION
• subatomic particles (electron, photon, etc)
have both PARTICLE and WAVE properties
• Light is electromagnetic radiation crossed electric and magnetic waves:
Properties :
Wavelength, l (nm)
Frequency, n (s-1, Hz)
Amplitude, A
constant speed. c
3.00 x 108 m.s-1
7.1
Properties of Waves
Wavelength (l) is the distance between identical points on
successive waves.
Amplitude is the vertical distance from the midline of a
wave to the peak or trough.
7.1
Atomic Line Spectra
• Bohr’s greatest contribution to
science was in building a
simple model of the atom.
• It was based on understanding
the SHARP LINE SPECTRA
of excited atoms.
Niels Bohr (1885-1962)
(Nobel Prize, 1922)
Line Spectra of Excited Atoms
• Excited atoms emit light of only certain wavelengths
• The wavelengths of emitted light depend on the
element.
H
Hg
Ne
Jellyfish lamps made with noble
gases artist- Eric Ehlenberger
7.3
7.3
Uncertainty Principle
Problem of defining nature of
electrons in atoms solved by
W. Heisenberg.
It is impossible to describe the
exact location of an electron.
W. Heisenberg
1901-1976
II.
Quantum theory
A. ground state – when electrons are in their lowest energy
B.
1.
4 quantum numbers
principle quantum number
a.
b.
energy level, n, 1,2,3,4,5
the greatest number of electrons in an
energy level is indicated by the
equation - 2n2
2.
energy sublevels and orbital
a.
energy states in an energy level, l
b.
the number of energy states = the energy level
i.
1 has 1, 2 has 2 ect
ii.
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special people
deserve fudge
3.
orientation in space
a.
s - spherical
b.
p - dumbbell x,y, z
c.
d - 5 orientations
d.
f-7
4.
spin of electrons
a. electrons spin - must have opposite spins
in order to be in same orbital
b.
orbital - space occupied by a pair of electrons
(s orbitals)
1s
7.6
p Orbitals
• The three p orbitals lie 90o apart in space
(d orbitals)
7.6
f
Orbital
principal quantum number n
n = 1, 2, 3, 4, ….
n=1
n=2
n=3
7.6
Boundary surfaces for all orbitals of the
n = 1, n = 2 and n = 3 shells
n=
3d
3
2
There are
n2
orbitals in
the nth SHELL
1
The last quantum number is the spin quantum
number
Electrons act as though they spin about an axis through their ce
Because there are two directions in which they can spin,
the spin quantum number has 2 values
Orbital diagram
Use lines to represent the orbital's
and arrows to represent electrons
H
1s
“Fill up” electrons in lowest energy orbitals (Aufbau principle)
??
CBBe
Li
65 3
electrons
4
electrons
electrons
electrons
H 1 electron
He 2 electrons
7.7
The most stable arrangement of electrons
in subshells is the one with the greatest
number of parallel spins (Hund’s rule).
C810
N
97
6electrons
electrons
electrons
Ne
OF
electrons
7.7
Paramagnetic
unpaired electrons
2p
Diamagnetic
all electrons paired
2p
7.8
Electron configuration is how the electrons are
distributed among the various atomic orbitals in an
atom.
number of electrons
in the orbital or subshell
1s1
principal quantum
number n
Sublevel (angular momentum)
quantum number l
7.8
“Fill up” electrons in lowest energy orbitals (Aufbau principle)
??
C 6 electrons
Li 34electrons
Be
electrons
B
Li
Be
1s2 2
1s
B 5 electrons
1s
2s122
2s
2s22p1
H
He12electron
electrons
He
H 1s
1s12
7.7
The most stable arrangement of electrons
in subshells is the one with the greatest
number of parallel spins (Hund’s rule).
C 97
N
O
F
Ne
6
810
electrons
electrons
electrons
N
CNe
FO
22 2
22
1s
1s
1s
1s
1s
22 2
2
2
2s
2s
2s
2s
2s
32p
26
54
2p
2p
2p
2p
7.7
Noble gas notation
Use the nearest noble gas that is behind the element
and then add to it
e.g write the noble gas notation for Na
Ne is the nearest noble gas – its configuration is
1s2
2s2
2p6
Therefore [Ne] indicates 1s2 2s2 2p6
Na would be [Ne] 3s1
What is the electron configuration and noble gas
notation of Mg?
Mg 12 electrons
1s < 2s < 2p < 3s < 3p < 4s
1s2
2s2
2p6
3s2
2 + 2 + 6 + 2 = 12 electrons
[Ne] = 1s22s22p6
Abbreviated as [Ne]3s2
7.8
What are the possible quantum numbers for the
last (outermost) electron in Cl?
Cl 17 electrons
1s2
2s2
2p6
3s2
3p5
1s < 2s < 2p < 3s < 3p < 4s
2 + 2 + 6 + 2 + 5 = 17 electrons
Last electron added to 3p orbital
n=3
l=p
Try These!
• Write the shorthand (Noble
gas notation) for:
2 3d9
[Ar]
4s
Cu
2 4f14 5d4
[Xe]
6s
W
2 4f14 5d9
[Xe]
6s
Au
Electron dot diagrams
Valence electrons – those electrons in the outer most
energy Level (those with the highest number)
Mg12
1s2
2s2
2p6
3s2
Mg
Mg has 2 valence electrons
Fe26
1s2
2s2
3s2
4s2
2p6
3p6
Fe only has 2 valence electrons
3d6
Fe
S16
1s2
2s2
2p6
3s2
3p4
S
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Isotopes are atoms of the same element (X) with different
numbers of neutrons in their nuclei
Mass Number
A
ZX
Atomic Number
1
1H
235
92
2
1H
U
Element Symbol
(D)
238
92
3
1H
(T)
U
2.3
2.3
Do You Understand Isotopes?
d.
Canal rays - in 1886 Eugen Goldstein observed a cathode ra
tube also generates a stream of positively charged particles
14
How many protons, neutrons, and electrons are in 6 C ?
6 protons, 8 (14 - 6) neutrons, 6 electrons
How many protons, neutrons, and electrons are
11
in 6 C ?
6 protons, 5 (11 - 6) neutrons, 6 electrons
2.3
Odds and ends
VI.
Hund’s rule - electrons must be placed in each
orbital before pairing them up
VII.
Valance electrons - those in the outer most energy level
- gives elements its chemical properties
VIII.
orbital notation - lines
IX.
Electron configuration -
1s2 2s2 2p6
X.
Nobel gas notation - {Ar} 4s1
XI.
Electron dot notation - only use the valance electron
On page 118
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