Model of
the Atom
IGCSE Chemistry
Learning Points
One Two Three
Describe key
Explain what an
Name the three types properties of the
isotope is and provide
of subatomic particle. three subatomic
an example.
particles.
What are atoms?
Atoms make up everything in the world - Basic
Building Blocks.
All atoms are neutral, meaning that they have no
overall charge.
Elements are made up of only one type of atom.
Periodic Table of Elements
Subatomic -
Particles
Atoms are made up of + +
three subatomic particles:
Protons
Neutrons
Electrons -
-
Nucleus
Nucleus
The nucleus is the centre of
+ +
the atom. It is where all of the
mass of the atom is
contained.
-
-
Protons
Positively charged
+ + subatomic particles
Charge denoted as +1
Have a relative weight of
1
-
Neutrons
-
Subatomic particles
having no charge - + +
neutral
Charge denoted as 0
Have a relative weight of
1
-
-
Electrons
Negatively charged
subatomic particles
+ + Charge denoted by -1
Located in shells around
the nucleus
Have a relative weight of
1/1840
-
Summary
Location in Relative Relative
the atom Charge weight
Proton Nucleus +1 1
Neutron Nucleus 0 1
Electron Shells -1 1/1840
Electron Configuration
Atoms can have multiple shells of electrons. The electrons
are arranged in a specific way:
The first shell can hold 2 electrons
The second shell can hold 8 electrons
The third shell can hold 8 electrons
The earlier shells must be filled before the next shell
can be occupied
Looking at Electron Configuration
Ne Cl
Neon atoms have 10 electrons. The Chlorine atoms have 17 electrons. The
electron configuration of neon is 2,8. electron configuration of chlorine is 2,8,7.
Relative Atomic Mass
3 Atomic (proton) number = the number of
protons (also the number of electrons). -
Li
Relative atomic mass = the total mass of +
7 the nucleus (protons and neutrons). + -
+
Elements can be found in the periodic table. The numbers next to
the chemical symbols in the periodic table, provide information
about the numbers of subatomic particles. A lithium atom has 3 -
protons, 4 neutrons and 3 electrons.
Isotopes Hydrogen-1
Isotopes are atoms of the same
element with different numbers
of neutrons. For example, Hydrogen-2
hydrogen has three isotopes with
the same number of protons and
electrons, but different numbers
of neutrons. Hydrogen-3
Practice Questions
Determine the number of protons, electrons, and neutrons in an atom of element X
with atomic number 29 and mass number 63
Protons
The number of protons of element X is the same as the atomic number
Number of protons = 29
Electrons
The neutral atom of element X, therefore, also has 29 electrons
Neutrons
The atomic number of an element X atom is 29, and its mass number is 63
Number of neutrons = mass number – number of protons
Number of neutrons = 63 – 29
Number of neutrons = 34
Practice Questions
Cobalt is an element in Period 4 of the Periodic Table
Complete the table below:
Number of Number of Number of
Particle
Protons Neutrons electrons
Co 27 32 27
Co +2
Co +3
Practice Questions
Explain the term Isotope.
Explain why two isotopes of the same element have identical chemical
properties but different physical properties.
State One industrial and one medical use of radioactive isotopes.
Locating tumors
Tracking leakages
