IB CHEMISTRY - Topic 2 Atomic Structure Notes

IB CHEMISTRY:
TOPIC 2 ATOMIC STRUCTURE NOTES

2.1 The nuclear atom

Subatomic particles and atomic structure
 Atoms are made up of a nucleus containing:
o Positively charged protons
o Neutrons with no charge
o Electrons with negative charge moving around the nucleus in shells/orbitals
 Electrons are assumed to have negligible mass.

Subatomic Relative mass Relative charge
particle
KEY DEFINITIONS
Proton 1 +1
Neutron (A) – Sum of the
Mass number 1 number of protons
0 and neutrons in the nucleus

AtomicElectron 1
number (Z) – The number -1 nucleus. Since atoms are electrically
of protons in the
1836is also equal to the number of electrons
neutral, the number of protons
Isotope – Atoms of the same element with the same number of protons, but with a
different number of neutrons. Isotopes differ in physical properties but have the same
chemical properties.

Nuclear Notation
 Nuclear notation shows the mass number, atomic
number and symbol to represent a particular isotope.
To find:
o Atomic Number (Z): Number of protons
o Mass Number (A): Number of protons and
neutrons
o Number of electrons = atomic number – charge




Properties of isotopes
 Chemical properties all depend on outer shell electrons. Since isotopes still have the
same number of electrons, their chemical properties will remain the same
 Physical properties depend on their nuclei. Since the number of neutrons changes,
properties such as size, speed, mass, density, rate of diffusion, melting and boiling
change, solubility will all differ between isotopes.

, Uses of radioisotopes
 Many isotopes are radioactive because the nuclei are more prone to breaking down
spontaneously. Radiation is emitted when this happens. Radioisotopes can occur
naturally or be man-made.
 Uses of radioisotopes include:

Carbon-14
 Carbon-14 is used to estimate the age of organisms (carbon dating)

Cobalt-60
 Cobalt-60 is a powerful gamma emitter, making it useful for the treatment of cancer

Iodine-131/Iodine 125
 Iodine-131 releases both gamma and beta radiation
 It can be used to treat thyroid cancer, and detect if the thyroid is functioning correctly




Mass Spectrometry (link to Topic 11)
 A mass spectrometer is an instrument that can be used to measure the individual
masses of atoms
 A mass spectrometer separates individual isotopes from a sample of atoms and
determines the mass of each isotope
 The operation of the mass spectrometer can be broken down into four stages:

1. VAPORIZATION: The sample is
heated and vaporized, and passed
through into an evacuated tube – this
separates the particles.

2. IONIZATION: The atoms/molecules are
then bombarded by a stream of high
energy electrons, knocking electrons off
the particles, resulting in ions with a 1+
charge


3. ACCELERATION: The positively charged ions are then accelerated along the
tube by means of the attraction to negatively charged plates. The ions pass
through the slits, which control the direction and velocity of their motion

4. DEFLECTION: The ions are then passed into a very strong magnetic field,
deflecting the ions in a curved path


5. DETECTION: The ions are detected electronically by a device that measures the
location and the number of particles