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Topic 1- Atomic structure and the periodic table

Measures of central tendency
Proton
Neutron
Electron

Actual mass
1
...
675 × 10!"#
9
...
602 × 10!$%
0
1
...
g
...
This means that isotopes
share the same number of protons but doesn’t share the same number of
neutrons
...
000
&'()$#'* +,'-+)'
...
12 +3 '4'
...
+// 12 13' +#1
...
000
Relative molecular mass
- Definition: The weighted mean of one mole of normal sample of the
!
substance relative to !"#$ the mass of 12C isotope having a value of
12
...
'+3
...
74+ 73(# 12 #$' /76/#+35'
- 𝑀𝑟 =
!
!"#$

#$'
...
12 5+-613 !"8

Mass spectrometry (take gaseous atoms and bombard them with electrons
- For testing the mass of a compound, and determine proportions
- Peak intensity gives the relative abundance – the final peak in a mass
spectrum is due to the molecular ion
1) Sample is vaporized to become gas
2) Sample gets ionized (ionization) using the electron gun
3) The ions are accelerated by an electric field
4) The accelerated ions pass through a magnetic field and are deflected
5) The ions are detected and recorded based on different masses and
quantity (heavier, less it deflected
...


Electron shells
- Electrons have the same energy value, opposite spin values
- First shell: 2 electrons in an S subshell

1S ↿⇂
-

-

-

Second shell: 8 levels, 2 energy levels
Lower level – 2 electrons, S subshell
Higher level – 6 electrons, P subshell
à Electrons in the P subshell are found in 3 different regions of the atom:
“x”, “y”, “z”

2P ↿⇂↿⇂↿⇂
2S ↿⇂

Third shell: 18 electrons, 3 energy levels
Lower level – 2 electrons, S subshell
Next highest – 6 electrons, P subshell
Highest – 10 electrons in the d subshell
4s subshell is filled before the 3D subject since there is overlap between
the energy levels of the subshell
4S subshell is filled before the 3d subshell since there is overlap between
the energy levels of the subshell

ℛ𝒰ℒℰ𝒮
Electrons
è Lower energy levels are filled before higher level ones (Aufbau
principle)
è Lower subshells are filled before higher ones
è Occupying using 1 electron if possible (Pauli’s exclusion principle)
è Occupying the same orbital if they have opposite spins
- Orbital order: 1S, 2S, 2P, 3S, 3P, 4S, 3D, 4P
*An exactly half full or full subshell is particularly stable*
Elements can be classified as s, p, d- block elements
-

Electronic configuration
developed from:
The atomic
emissions spectrum
provides evidence
for the existence of
quantum shells
Successive
ionization energies
provide evidence
for the existence of
quantum shells and
the group which the
element belongs
The fact that the first
ionization energy of
successive elements
provides for electron
sub-shells

Ionization energy
Successive ionization energies
- Definition – The energy required to take away one mole of electron to
infinity from one mole of gaseous ions to form one mole of gaseous
positive ions
- Definition for second ionization energy – The energy required to
remove one mole of electrons to infinity from one mole of gaseous
unipositive ions to form one mole of gaseous dipositive ions (and so
forth for 3rd ionization energy etc
...
The large increases can also
be used to predict the group of an unknown element
First ionization energy
- Definition – The energy required to take away one mole of electrons to
infinity from one mole of gaseous atoms to form one mole of gaseous
positive ions

𝑥(") → 𝑥 $% + 𝑒 &
-

The ionization energy depends on the distance, charge, and the
shielding
...
This
reduces the attraction between the nucleus and the electrons in the
outer shell
...
The shielding effect increases as the
number of inner shell increases which increases the distance of the
outermost electron from the nucleus which reduces the attraction
between the nucleus and the outermost electrons which therefore
reduces ionization energy (if shielding increases)
...

è There are slight drops in some cases since the electrons start to fill
the other subshell, which reduces the attraction between the
nucleus and that outermost electron
...

è It rises as metals contribute more electrons to the cloud
è There is a big rise for giant molecules on group 4
è And it decreases for simple molecules with weak intermolecular
forces
Period 2 & 3
First ionization energy

Melting and boiling points

Electromagnetic spectrum
Infrared à visible light (from red to violet) à UV light
Visible light:
- Red color
è Higher wavelength
è Low energy photons
è Low frequency
- Violet color
è Low wavelength
è High energy photons
è High frequency
è High energy
Line spectrum – the lines of the spectrum shows the energy levels (discrete lines)
When there is heat, electrons will be excited and go to the next energy levels
...

𝑐 = 𝑥𝑓
𝐸 = ℎ𝑓
N3àN2 – Red light
where
c
is
speed
of
where
E
is energy, h is
N4àN2 – Light blue light
light, x is wavelength,
constant, f is
N5àN2 – Dark blue light
f is frequency
frequency charge

𝐸 ∝ 𝐹 (Energy proportional to frequency)
Continuous spectrum
- A nichrome wire is used
- Dip it into concentrated HCL in order to clean the wire
- The dip it into the salt
- Put it in the flame of the Bunsen burner



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