Ball of positive charge with
electrons scattered in it
Cloud of electrons
Dalton initially believed
atoms were tiny
undividable spheres
Replaced Thomson’s Plum Replaced
with --> Pudding model with -->
Discovered
electrons
New evidence leads
to new models
Tiny positive nucleus
at the centre
Rutherford’s
nuclear model
Bohr
model
Replaced
with -->
Alpha particle
scattering experiment
Electrons orbit
in shells
Atomic Model Development
Atomic Structure
1.1 ATOMIC
STRUCTURE
Relative
masses
Protons: 1
Neutrons: 1
Electrons: Very small
Subatomic
Particles
Neutrons
Neutral
charge
Protons
Mass number (A)
Sum of protons and neutrons
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Atomic nucleus contains
protons and neutrons and is
surrounded by electrons
Electrons
Positively
charged
Negatively
charged
Same number of protons
and electrons in an atom
Atomic number (Z)
Number of protons
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Data analysis
Using masses and
abundances of each isotope
Ion detection
Calculate relative
atomic mass
Ion drift
Acceleration
Ionisation
For identifying
elements
Time of Flight (TOF)
mass spectrometry
E.g. Mg+(g) → Mg2+(g) + e-
Successive ionisation
energies equations
Determine relative
molecular mass
Mass
Spectrometry
Gives data about relative
isotopic mass and relative
abundance of isotopes
Isotopes
Same number of
protons, different
number of neutrons
1.1 ATOMIC STRUCTURE
Ionisation
energies
Electron
Configuration
First ionisation
energy
Successive ionisation energies give
evidence of configuration
in shells and subshells
Configurations of elements
up to Krypton
4s subshell filled
before 3d subshell as
it has lower energy
Lowest energy
subshells filled first
E.g. Fe:
1s22s22p63s23p63d64s2
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