Protons, Neutrons, Electrons - MOLEBUS (ALLCHEM)



Protons, Neutrons, Electrons

The atomic number of an element is defined as the number of protons an atom of that element has in its nucleus; in a neutral atom, this will also be

equal to the number of electrons the atom has.

Isotopes are atoms of the same element that have identical numbers of protons but different numbers of neutrons. Ions are made when an atom gains

Or loses electrons. The mass number of an atom is the number of protons plus the number of neutrons in the atoms’ nucleus.

The mass number is not found on the periodic table; it must be either given or be calculated. The mass number is used to identify isotopes of an

element.

For example, there are 2 different isotopes for Vanadium-50 and Vanadium-51. We can write this in different ways:

[pic]

You must remember what each of these numbers means, so that you can fully describe the isotope!

[pic]

• Protons: look it up on the periodic table to find its atomic number, which must equal the number of protons.

• Neutrons: The number of neutrons is never written you must calculate it! Since mass # = protons + neutrons, and atomic # = protons.

See above Vanadium: 51-23 = 28 neutrons.

• Electrons: Charge = (number of protons) – (number of electrons)

KEY THOUGHT: Unless you are shown it’s an ion you may assume that each line represents a neutral atom.

|Number of

Protons |Number of

Neutrons |Number of

Electrons |Atomic

number |Mass

number |Isotope name |Isotope

symbol | | |23 |28 |23 |23 |51 |Vanadium-51 |[pic] | | | | | | | | |[pic] | | |23 |28 |20 | | | | | | |47 | | | |109 | | | | |38 |50 | | | | | | | | | | | | | |[pic] | | | | |35 |35 |81 | | | | | | |36 | | |Bromine-79 | | | |22 | |18 | |46 | | | | | | | | | |Radium-223 | | | |74 |108 |72 | | | | | | | | | |8 |16 | | | | |8 |9 | | | | | | | | | | | | |Oxygen-18 | | | | | | | | | |[pic] | |

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Mass number

Ion charge (if none, it’s an atom, not an ion!

Atomic number

a)

b)

c)

d)

e)

f)

g)

h)

i)

j)

k)

l)

m)

n)

p)

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