Download Atomic Information

Atomic Information
• All atoms are composed of the same basic
particles, yet not all atoms are exactly the
same. Atoms of different elements have
different numbers of protons.
• The atomic number of an element is the
number of protons in the nucleus of that
element. Atoms of the same element have the
same number of protons.
(Number of Protons)
• Protons have a positive charge. Electrons have
a negative charge. Atoms are electrically
neutral in nature, which means that the
number of protons equals the number of
electrons.
• If electrons are added or taken away, the ratio
between protons and electrons becomes
imbalanced and the atom will have a charge.
Ions
• If electrons are added to the atom, then there
are more negative charges than positive
charges. The atom becomes negatively
charged and is called an anion.
• If electrons are removed from the atom, then
there are less negative charges than positive
charges. The atom becomes positively charged
and is called a cation.
• The size of the charge is easily calculated. Net
charge equals protons minus electrons.
• When an atom has a charge, it is written on
the upper right-hand corner of the element
symbol.
• Calcium ion has 20 p+ and 18 e– Charge is 20 – 18 = +2
» Symbol is Ca2+
• Bromine ion has 35 p+ and 36 e– Charge is 35 – 36 = -1
» Symbol is Br1-
The Neutron
• Early models of the atom only considered two
particles of the atom, the proton and the electron.
• The neutron has a mass about equal to the proton,
but has no charge. Having neutrons would not pose a
problem if all atoms of a particular element had the
same number of neutrons – but this is not the case!
• The number of neutrons can vary.
Isotopes
• Isotopes are atoms of the same element that
have different masses, due to the different
number of neutrons.
• The mass number is the number of protons
plus the number of neutrons in the nucleus.
The mass number is useful when designating
isotopes.
• To write an isotopic symbol, the mass number goes
on the top left-hand corner of the element symbol.
The number of protons (atomic number) goes on the
bottom left-hand corner of the element symbol.
• Oxygen – 17
– Means that the mass number is 17. Oxygen has 8 protons,
which means that there are 9 neutrons.
17 O
8
• Magnesium – 23
– Means that the mass number is 23. Magnesium has 12
protons, which means that there are 11 neutrons.
23 Mg
12
Atomic Notation
• Example:
37
Cl
17
17
• Number of Protons
• Number of Electrons 17
• Number of Neutrons 20
Neutrons = Mass Number – Protons
20 = 37 - 17
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