A detailed summary of the A level AQA Chemistry topic, Atomic Structure. Definitions and equations given in an easy and understandable way. Goes into detail about atoms, isotopes, electronic configurations, ionisation energies and mass spectrometry.
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Atomic structure
Atomic structure: nucleus contains protons and neutrons...electrons layed out on energy levels.
Atomic diameter = 1x10^10
Mass number (A) and atomic (proton) number (Z)
ATOMS
The mass is concentrated inside the nucleus.
Diameter of the nucleus: 10^ -15 m 1 (fentometre)
Diameter of atom: 10^ -10m
Carbon-12 is used as a comparison for the relative masses as the mass of a Carbon 12 is exactly 12.
Isotopes
Isotopes are atoms with the same number of protons but with a different number of neutrons.
Properties of isotopes
Property type Same/different Reason
Chemical properties identical Same number of electrons or same electronic configuration
Physical properties can differ Different mass numbers
Untitled
RELATIVE MASS AND CHARGE OF SUBATOMIC PARTICLES
Sub atomic particles Relative mass Relative charge Mass (kg)
Protons 1 +1 1.672x10^-27
Neutrons 1 0 1.675x10^-27
Atomic structure 1
, Sub atomic particles Relative mass Relative charge Mass (kg)
Electrons 1/1836 -1 9.109x10^31
Relative masses:
Relative atomic mass (Ar)
The Ar of an element is the weighted average of the masses of its isotopes relative to 1/12 of the
mass of a carbon -12 atom.
The mass of a carbon atom is always 12grams
Ar = averagemassperatomofanelement/1/12massofoneatomofcarbon − 12
12C=12.0g
12.0000 to 4dp
Relative isotopic mass
The relative isotopic mass of an isotope is the mass relative of the mass of a carbon -12 atom
Relative molecular mass (Mr)
This term should only be applied to substances which actually exist as molecules.
A molecule consists of a fixed number of atoms joined together by covalent bonds eg: CO2, N2
Relative formula mass (Mr)
Same symbol as relative molecular mass
Relative formula mass is a more useful term than relative molecular mass because it includes
everything, whatever the bonding.
It works just as well for ionic substances as for covalent substances —> should use this one all
the time.
Nucleon
Anything inside the nucleus; both protons and neutrons are regarded as nucleons
ELECTRON CONFIGURATION
LEVELS AND SUB-LEVELS
Atomic structure 2
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