Download Atomic Structure Cheat Sheet Atomic Number = p+ Mass Number

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Atomic Structure Cheat Sheet
Atomic number :
The atomic number of an element is the same number as the number of protons (p+) in each atom of that element.
It is the whole number on the periodic table.
For example, the element sodium (Na) has atomic number 11. That means that an atom of sodium will always have
11 protons.
Atomic Number = p+
Mass number:
The mass number is the sum of the number of protons (p+) and the number of neutrons (no). It is also a whole
number but is not on the periodic table. It can be determined for any element when you know the number of
neutrons.
For example, if an atom of sodium (Na) has 12 neutrons, the mass number is 23 because 11 p+ + 12 no = 23.
Mass Number = p+
+
no
Number of neutrons:
To determine the number of neutrons, just subtract the number of protons from the mass number.
For example, if an atom of sodium (Na) has a mass number of 23 and 11 protons, then the number of no = 23 – 11 =
12.
Number of no = mass number - p+
Atomic charge:
The charge of an atom depends on the number of protons and electrons (e-). If there are more protons, the
charge is (+). If there are more electrons, the charge is (-). If the number of protons and electrons are equal, the
atom is neutral. To determine the atomic charge, subtract the number of electrons from the number of protons.
For example, it an atom of chlorine has 18 electrons, the charge is 17 p+ – 18 e- = -1
Atomic charge = p+ –
e-
Atomic number
11
p+
Na
Element symbol
nuclear symbol is:
and can be used for
An example of a
Atomic mass
Sodium
Element name
An example of a
22.99
ISOTOPES.
chemical symbol for an ion is:

A positively charged ion is a CATION, such as Ag+1

A negatively charged ion is an ANION, such as Br-1
+1
Ag
and is used for
IONS.