Notesale: Turn your study into money

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Objectives:
 What is an atom?
 Labeled diagram of an atom
 Atomic structure
 Properties of the three sub-atomic particles
 Electronic configuration
 Atomic numbers and mass numbers
 Calculation of protons, neutrons and electrons
 Valence shell

What is an atom?
 An atom is the smallest particle of an element that can

exist and still have the properties of that element
...
)
Atoms are composed of two parts:
 A central nucleus containing the protons and neutrons

tightly packed together
...
)
 One or more shells or energy levels surrounding the

nucleus containing electrons revolving at high speeds
...
)
 Protons and neutrons are found inside the nucleus of

the atom
...


Labeled diagram of an atom

nucleus

Particle

Relative mass

Relative charge

Location

Protons

1

+1

Inside the nucleus

Neutrons

1

Neutral

Inside the nucleus

Electrons

1/1840 or 0

-1

Outside the
nucleus

 The nucleus of the atom has a positive charge due to

the presence of the protons
 The space has a negative charge due to the presence of

the electrons

 The atom is overall neutral as there are equal positive

and negative charges, i
...
the number of protons and
electrons in an atom is always the same
...
This arrangement is called the electronic
configuration
...

 The second shell contains a maximum of eight (8)

electrons
...


Atoms (contd
...

 The shells become nearer to each other as their

distance from the nucleus increases
...


 Atoms of different elements are different because they

contain different numbers of protons, neutrons and
electrons
...

 The atomic number is unique to a particular element
...


Mass number (contd
...

 The electrons in the this outer shell are the ones that

take part in chemical bonding and are known as
valence electrons
...


 During chemical changes or reactions these valence

electrons are rearranged
...
e
...


Ions
 A particle is described as an ion rather than an atom

when the number of electron(s) is not equal to the
number of protons
...
e The charges of the sub-atomic particles do not

cancel each other out
...
, i
...
they
are positively or negatively charge particles
...
Cations contain more

protons than electrons
...
Anions contain more

electrons than protons
...
)
 NB When an atom loses or gains electrons ONLY the

ELECTRONS are affected
...

 Non-metals gain electrons to form negative ion
...
)
 Ions are chemically inactive and stable because they

have the electronic structure of the noble gases

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