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Atoms are made up of three particles:
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Protons
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Neutrons
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Electrons
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Question: Which of the three particles identifies what element an atom is?
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The PROTON ! (very important)

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In any element, the # of protons is always constant.
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Unlike the number of protons, the number of electrons and neutrons can vary within an element without changing the identity of the element.
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Ex. Carbon (C) ALWAYS has 6 protons, but it can have anywhere from 6-8 neutrons and 2-10 electrons

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An ISOTOPE is a form of an element that has a different number of neutrons than
“normal”
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Carbon has three isotopes
Notice how the # of protons does NOT change!

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Most atoms have naturally occurring isotopes including:
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Radon
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Potassium
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Uranium
• When an element is “radioactive” it means it has an unstable number of neutrons (an unstable ISOTOPE)

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An atom usually has a neutral charge. That means it has the same number of protons as electrons
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Remember, a proton has a positive charge and an electron has a negative charge
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ION
– an atom that has lost or gained one or more electrons and has become charged either positively or negatively

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When an atom LOSES electrons, it becomes more POSITIVE
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Why?
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If you are getting rid of negative particles
(electrons) but your number of positive particles (protons) are staying the same.
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In other words, you are subtracting negative numbers

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What would the charge be if:
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The neutral form of Gold (Au) lost 4 of its
79 electrons. It now has 79 protons and 75 electrons
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The neutral form of Mg lost 2 of its 12 electrons. It now has 12 protons and 10 electrons.

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When an atom GAINS electrons it becomes more NEGATIVE
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Why?
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Electrons have a negative charge, so the more you have, the more negative you become

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Ions are represented by placing a
“superscript” charge number next to the atomic symbol.
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Ex.
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O -2 = oxygen with a negative 2 charge
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K + = potassium with a positive 1 charge
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N -3 = nitrogen with a negative 3 charge
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And so on

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The elements, as they are found on the periodic table, are neutral atoms and their mass is an average of all isotopes
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Remember the atomic mass is the average of ALL isotopes, but when we round it for calculating the number of neutrons, we always get the most abundant isotope.

• How many P’s, N’s, and E’s does each of the following have?
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Label each as an isotope, ion, or the version found on the P.T.