Transcript Compounds and Bonding

Atoms, Ions, and Isotopes
Quick Review
• Atoms are made up of three particles:
• Protons
• Neutrons
• Electrons
• Question: Which of the three particles
identifies what element an atom is?
• The PROTON! (very important)
Different Forms of the Same
Element
• In any element, the # of protons is always
constant.
• Unlike the number of protons, the number
of electrons and neutrons can vary within an
element without changing the identity of the
element.
• Ex. Carbon (C) ALWAYS has 6 protons, but it
can have anywhere from 6-8 neutrons and 2-10
electrons
Isotopes
• An ISOTOPE is a form of an element that
has a different number of neutrons than
“normal”
• Carbon has three isotopes
Notice how the # of
protons does NOT
change!
Other Isotopes
• Most atoms have naturally occurring
isotopes including:
• Radon
• Potassium
• Uranium
• When an element is “radioactive” it means
it has an unstable number of neutrons (an
unstable ISOTOPE)
IONS
• An atom usually has a neutral charge. That
means it has the same number of protons as
electrons
• Remember, a proton has a positive charge and an
electron has a negative charge
• ION – an atom that has lost or gained one
or more electrons and has become charged
either positively or negatively
Positive Ions
• When an atom LOSES electrons, it
becomes more POSITIVE
• Why?
• If you are getting rid of negative particles
(electrons) but your number of positive
particles (protons) are staying the same.
• In other words, you are subtracting negative
numbers
Examples
• What would the charge be if:
• The neutral form of Gold (Au) lost 4 of its
79 electrons. It now has 79 protons and 75
electrons
• The neutral form of Mg lost 2 of its 12
electrons. It now has 12 protons and 10
electrons.
Negative Ions
• When an atom GAINS electrons it becomes
more NEGATIVE
• Why?
• Electrons have a negative charge, so the
more you have, the more negative you
become
Representing Ions
• Ions are represented by placing a
“superscript” charge number next to the
atomic symbol.
• Ex.
• O-2 = oxygen with a negative 2 charge
• K+ = potassium with a positive 1 charge
• N-3 = nitrogen with a negative 3 charge
• And so on
Periodic Table
• The elements, as they are found on the
periodic table, are neutral atoms and their
mass is an average of all isotopes
• 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.
Examples
Examples
• How many P’s, N’s, and E’s does each of the
following have?
• Label each as an isotope, ion, or the version
found on the P.T.