atomic structure materials science asst. prof. dr azeez ... · asst. prof. dr azeez barzinjy. the...
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A beryllium atom has 4 protons, 5
neutrons, and 4 electrons. What is the
mass number of this atom?
a) 4
b) 5
c) 8
d) 9
e) 13
Atomic structure
The smallest particle into which an element can be
divided and still have the properties of that
element
a) nucleus
b) electron
c) atom
d) neutron
How would you describe the nucleus?
a) dense, positively charged
b) mostly empty space, positively charged
c) tiny, negatively charged
d) dense, negatively charged
Atomic structure
Where are electrons likely to be found?
a) in the nucleus
b) in electron clouds
c) mixed throughout an atom
d) in definite paths
Every atom of a given element has the same
number of
a) protons
b) neutrons
c) electrons
d) isotopes
Atomic structure
What is the meaning of the word atom?
a) dividable
b) invisible
c) hard particles
d) not able to be divided
Which statement is true about isotopes of the
same element?
a) They have the same number of protons
b) They have the same number of neutrons
c) They have a different atomic number
d) They have the same mass
Atomic structure
Which has the least mass in an atom?
a) nucleus
b) proton
c) neutron
d) electron
If an isotope of uranium, uranium-235, has 92
protons, how many protons does the isotope
uranium-238 have?
a) 92
b) 95
c) 143
d) 146
Atomic structure
A carbon atom with 6 protons, 6 electrons, and 6
neutrons would have a mass number of
a) 6
b) 12
c) 15
d) 18
The number at the top is the
a) atomic number
b) element name
c) atomic mass
d) chemical symbol
Atomic structure
How many electrons does a neutral Cl atom
contain?
a)16
b)17
c)18
d)19
What is the difference between atomic mass and
atomic weight?
Atomic structure
Atomic Structure
Neutral atoms have the same number
of protons and electrons.
Ions are charged atoms.
●cations – have more protons than
electrons and are positively charged
●anions – have more electrons than
protons and are negatively charged
If a neutral atom looses one or more electrons
it becomes a cation.
If a neutral atom gains one or more electrons
it becomes an anion.
Na 11 protons
11 electrons Na+ 11 protons
10 electrons
Cl 17 protons
17 electrons Cl- 17 protons
18 electrons
Atomic Structure
e- +
+ e-
electrons are assumed to
revolve around the atomic
nucleus in discrete orbitals,
and the position of any
particular electron is more
or less well defined in terms
of its orbital.
Electrons are permitted to
have only specific values of
energy.
Bohr Atomic model
Bohr Atomic model
excitation vs relaxation
An electron may change
energy by making a quantum
jump either to an higher
energy (with absorption of
energy) or to a lower energy
(with emission of energy).
excitation relaxation
Quantum Mechanics
Unfortunately, extremely small particles
(electrons) do not follow the laws of classical
(Newtonian) physics. The new physics that
mathematically treats small particles is called
Quantum Mechanics.
electron distribution
wave-mechanical model
an electron is no longer treated
as a particle moving in a discrete
orbital;
electron is considered to exhibit
both wavelike and particle-like
characteristics.
The position of an electron is
described by a probability
distribution // electron cloud.
Quantum Mechanics Wave behavior is described with the wave function
ψ, incorporating the wave and particle features of
electrons (Erwin Schrödinger)
The probability of finding an electron in a certain
area of space is
proportional to ψ2
electron density.
Austrian; 1933 Nobel
prize in physics
Quantum Mechanics
Heisenberg’s uncertainty principle more precisely the position of some particle is determined, the less precisely its momentum can be known
A macroscale analogy…
High Shutter Speed Low Shutter Speed
Can judge location, Can judge speed,
but not speed. But not location
we cannot precisely measure the momentum and
the position of an electron at the same time.
As the momentum of the electron is more and more
certain, the position of the electron becomes less
and less certain, and vice versa.
n = 2.5 cannot exist as a principal quantum number.
There must be an integral number of wavelengths
(n) in order for an electron to maintain a
standing wave. If there were to be partial waves,
the whole and partial waves would cancel each
other out and the particle would not move.
Heisenberg’s uncertainty principle
Quantum Mechanics The Schrödinger equation
specifies possible energy states
an electron can occupy.
The energy states and wave
functions are characterized by
a set of quantum numbers.
Instead of orbits in the Bohr
model, quantum numbers and
wave functions describe atomic
orbitals.
every electron in an atom is characterized by four
quantum numbers.
There are three quantum numbers necessary to
describe an atomic orbital.
The principal quantum number (n)
designates size
The angular moment quantum number (l)
describes shape
The magnetic quantum number (ml)
specifies orientation
quantum numbers
Principal Quantum Number (n)
designates the size of the orbital.
Larger values of n correspond to larger orbitals.
The allowed values of n are integers: 1, 2, 3 and so
forth.
A collection of orbitals with the same value of n is
frequently called a shell.
n
K L M N O P .......
1 2 3 4 5 6 ……
Angular moment Quantum Number (l)
signifies the subshell
describes the shape of the orbital.
l values range from 0 to n – 1
Example: If n = 2, l can be 0 or 1.
n 1 2 3 4 5 6
l
subshell
0 1 2 3 4 5
s p d f g h
energy state 1 3 5 7 9 11
Magnetic Quantum Number (ml)
describes the orientation of the orbital in space.
ml are integers that depend on l: – l,…0,…+l
ml identifies # of energy states for each subshell
For an s subshell: a single energy state
For p, d, and f subshells: 3, 5, and 7 energy states
Principal
Quantum No: n
Shell
Subshell
l No. of energy States:
ml
Number of Electrons
Per Subshell Per Shell
1 K s /0 1 / 0 2
2
2 L s / 0 1 / 0 2
8 p / 1 3 / -1,0,+1 6
3 M s / 0 1 / 0 2
18 p / 1 3 / -1,0,+1 6
d / 2 5 / -2,-1,0,+1,+2 10
4 N
s / 0 1 / 0 2
32 p / 1 3 / -1,0,+1 6
d / 2 5 / -2,-1,0,+1,+2 10
f / 3 7 / -3,-2,-1,0,+1,+2,+3 14
5 O
s / 0 1 / 0 2
50 p / 1 3 / -1,0,+1 6
d / 2 5 / -2,-1,0,+1,+2 10
f / 3 7 / -3,-2,-1,0,1,2,3 14
g / 4 9 / -4,-3,-2,-1,0,+1,+2,+3,+4 18
6 P
s / 0 1 / 0 2
72
p / 1 3 / -1,0,+1 6
d / 2 5 / -2,-1,0,+1,+2 10
f / 3 7 / -3,-2,-1,0,1,2,3 14
g / 4 9 / -4,-3,-2,-1,0,1,2,3,4 18
h / 5 11 / -5,-4,-3,-2,-1,0,+1,+2,+3,+4,+5 22
Number of available electron states for initial shells and subshells
An s subshell has one orbital which is spherically
shaped.
If you were to measure where the electron was
within an s subshell many, many times and plot
the results on a graph you would get something
like this.
Atomic orbitals