Protons, Neutrons and Electrons... Oh my!
Isotopes and Ions
Sep 30­4:00 PM
Atomic Number
Vocabulary:
The number of protons in an atom
Mass Number
The sum of the number of protons
and neutrons in the nucleus.
Isotopes
Atoms of the same
element with different
atomic masses.
Sep 30­4:02 PM
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Look at the periodic table and you will see that the atomic number determines the element's position in the table.
Because atoms are neutral, the number of protons and electrons must be equal. Thus, once you know the atomic number of an element, you know both the number of protons and the number of electrons.
Sep 30­4:31 PM
While it's true that all atoms of a particular element have the same number of protons and electrons, the number of neutrons may differ. Atoms such as these, with the same number of protons but different number of neutrons, are called isotopes.
To make it easy to identify each of the various isotopes of an element, chemists add the mass number after the element's name. The mass number represents the sum of the number of protons and neutrons in the nucleus.
Carbon ­ 12
Carbon ­ 14
Sep 30­4:31 PM
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For example, the potassium isotope with 19 protons and 20 neutrons has a mass number of 39, and the isotope is called potassium­39.
Chemists often write out isotopes using a shortened type of notation involving the chemical symbol, atomic number and mass number, as shown below. Note that the mass number is written as a superscript to the left of the chemical symbol, and the atomic number is written as a subscript to the left of the chemical symbol.
Sep 30­4:47 PM
Let's build some isotopes. Lithium has three isotopes: lithium­6, lithium­7 and lithium­8. What do these isotopes look like?
Lithium­6
Lithium­7
Lithium­8
Protons
Neutrons
Electrons
Sep 30­4:34 PM
3
Let's build more isotopes. Hydrogen has three isotopes, but they have special names. Their names are protium, deuterium, and tritium. What do these isotopes look like?
Protons
Neutrons
Electrons
Sep 30­4:34 PM
What we can know about Isotopes
Isotope Symbol
# of Mass # of # of Atomic Number Number Protons Electrons Neutrons Helium ­ 4 2 4 2 2 2 Nitrogen ­ 15 7
15 7 7 8 Vanadium ­ 52 23 52 23 23 29 Zinc ­ 64 30 64 30 30 34 Technetium ­ 99 43 99 43 43 56 Oct 18­9:00 PM
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Ion
Vocabulary:
An atom or bonded group of
atoms with a negative or positive
charge.
cation
An ion with a positive charge.
Forms when electrons
are REMOVED from
an atom.
anion
An ion with a negative
charge. Forms when electrons are added to
an atom.
Sep 30­4:02 PM
CATIONS
Cations are positive ions. Think about how the "t" in the word look kinda like a "+". These are formed when electrons are removed. So there are the SAME number of protons, but fewer electrons.
The left side of the periodic table (shown in shades of blue) is where cations occur.
Sep 30­4:31 PM
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Anions
When electrons are added to an atom, the atom becomes negatively charged. This is called an anion. Non­metals (right side ­ shown in yellow) always gain electrons.
Think :
"a n ion" = a negative ion
Negative ions change their name. The ions name is the root of the atom's name with the ending "ide".
So chlorine becomes "chloride", oxygen becomes "oxide", etc.
Sep 30­4:31 PM
Let's build some ions. Let's build a fluorine atom and a fluoride ion...
Let's build a magnesium atom and a magnesium ion...
Protons
Neutrons
Electrons
Sep 30­4:34 PM
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What we can know about Isotopes of Ions
Isotope Symbol
# of Atomic Mass # of # of Number Number Protons Electrons Neutrons Iron ­ 55 26 55 26 24 29 Nitride ­ 15 7
15 7 10 8 Vanadium ­ 52 23 52 23 20 29 30 64 30 28 34 35 80 35 36 45 Zinc ­ 64 Bromide ­ 80 64
30Zn+2 Oct 18­9:00 PM
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