Electrons In Atoms
Mr. O’Brien (SFHS)
Chapter 5
Standard 1D
Electrons in Atoms (std.1D)
• What are Bohr Models?
– planetary model in which the negatively-charged
electrons orbit a small, positively-charged nucleus
similar to the planets orbiting the Sun
• How are energy levels related to the periodic
table?
– The periodic table is divided into 7 energy levels
(they are the rows)
– Electrons of atoms are organized into these
energy levels.
(figure 1) The diagram to the left shows a
simple Bohr model. The “orbitals” indicate
where electrons orbit around the nucleus. The
orbitals, “energy levels”, are indicated by the
rows on the periodic table.
(figure 2) The Bohr Model can explain
how glow sticks work. When electrons
fall from higher energy orbitals to
orbitals closer to the nucleus, energy
is released in the form of light.
Main Points of Bohr Model
2.
1. Electrons contain energy.
Smaller orbits have less energy than larger ones.
Electrons In Atoms
(std.1D)
1. Look at the “row number” the element is in. Draw that
many energy levels.
2. Starting from atomic # 1, insert the electrons into their
appropriate level.
i.
•
For those between columns 3-12, place those electrons in
the previous level.
You try. Draw elements the following elements:
–
magnesium, chlorine, calcium, iron, scandium, arsenic.
Magnesium-24
Scandium-45
Chlorine-35
Arsenic-75
(figure 1) The figure above shows energy levels
divided into rows. Note: the electrons of the elements
in the “middle section” are placed into the previous
level.
Calcium-40
Iron-56
(figure 2) Examples of Bohr Models of several isotopes.
Electrons In Atoms (std.1D)
•
What are Valence Electrons?
–
•
Electrons in the outermost orbital
Why are they important?
1. Atoms gain or lose valence electrons for bonding
2. Atoms in the same group have similar chemical properties because they
have same # of valence é
•
Is there a short cut to find Valence Electrons?
–
•
Group # (column) represents amount of valence electrons.
What are Electron Dot Structures?
–
Simplistic way to represent an atom and its valance electrons
(figure 2) The valence electrons of Sodium is being
transferred to Chlorine to create a bond..
Examples of Electron dot Structures
(figure 1) These elements are all in the same group
(column) in the periodic table. Just by looking at them
you can see they have similar properties.
Electrons In Atoms (std.1D)
•
Octet rule: Atoms tend to gain, lose, or share e in order to
acquire a full set of eight valence é (noble gas).
–
–
•
Ion: an atom that gains or lose ve to have a positive or negative
charge.
–
–
•
Exception (helium)
Having all their valence é (8) make noble gases stable!
When atoms lose ve and form positively charged ions (cations)
When atoms gain ve, they form negative charged ions (anions).
Practice:
–
–
–
How many electrons will oxygen gain/lose to become a noble gas?
Identify the number of valence electrons for bonding in Magnesium.
Identify the number of electrons chlorine can accept for bonding.
All Elements Want To Be Like Noble Gases!
Bohr Model (HONORS)
•
In addition to principle quantum #, the
electrons are also organized into 4 sublevels.
– s,p,d,f
•
The sub-levels indicate the shape of the
electrons orbit. (see examples)
(figure 1) The figure above shows the division
of the periodic table according to sub-levels.
First Four Principal Energy Levels
(figure 2) The figure above shows the shapes of the sublevels. This is were the electrons
are actually located. The “s” sub-levels are simple orbits around the nucleus. The “p” sublevels are areas above/below or on the side of the nucleus where electrons are located.
The “d” sub-levels are similar but they protrude out in other angles outside the nucleus.
Principal quantum number (n)
Sublevels present
1
s
2
sp
3
spd
4
spdf
(figure 3) A more accurate representation of an atom.
Note electrons are located in different areas around
the nucleus according to their sublevels.
Bohr Model
(HONORS) (cont.)
• Another way to organize electrons
following the periodic table.
• Rules to follow:
– The Aufbau Principle: each é occupies
the lowest energy orbital available.
(figure 1) Notice in the energy level
diagrams that sub-levels “d” have more
energy than the previous “s” group.
Because the “d” sub-levels have more
energy we must first place electrons in
the “s” sub-level before the “d” sub-level.
Writing Electron Configurations
(HONORS)
•
Electron configurations are a way to organize
electrons by indicating the following:
i. the level they are in
ii. the shape (sub-level) of the orbital
iii. the number of electrons in that sub-level
•
You try. Write the following electron configurations:
–
–
–
–
–
•
carbon, neon, potassium, zinc, bromine.
C → 1s2 2s2 2p2
Ne → 1s2 2s2 2p6
K → 1s2 2s2 2p6 3s2 3p6 4s1
Br → 1s2 2s2 2p6 3s2 2p6 4s2 3d10 4p5
Writing “abbreviated” electron configurations.
–
–
–
Substitute the last element from column 18/8A in your
configuration.
Ex: carbon [He] 2s2 2p2
You try. Write the previous examples using the
“abbreviated” method.
•
•
•
Ne → [Ne]
K → [Ar] 4s1
Br → [Ar] 4s2 3d10 4p5
(figure 1) See the images above and below for a
visual explanation of writing electron configurations.
Honors Info
• Quantum: minimum amount of energy
that can be gained or lost by an atom.
– Matter can gain or lose energy only in small,
specific amounts called quanta.
– Photon: particle of electromagnetic
radiation with no mass that carries a
quantum of energy.
– Photoelectric effect: photons are kicked off
by the metal when light with enough energy
strikes it.
• Atomic Emission Spectrum: a set of
frequencies of the electromagnetic
waves emitted by atoms of the element.
– Each element atomic emission spectrum is
unique and can be used to identify element.