Atoms and Molecules
Protons, Neutrons and Electrons
Protons
Found in
Charge
# of each
Type of element
nucleus
+1
Same as electrons
Determines
atomic number
Proton
Neutron
Electron
Neutrons
nucleus
Electrons
Orbiting the nucleus
neutral
-1
Can vary
Same as protons
What’s wrong with this atom?
Proton
Neutron
Electron
A. Too many neutrons
B. # of particles in nucleus
is the same as the
electron #
C. Too many electrons
D.Too many protons
What element is this?
Proton
Neutron
Electron
A. Helium
B. Carbon
C. Oxygen
D.Not enough information
to determine
What element is this?
A. Carbon
B. Beryllium
C. Magnesium
Isotopes
• The atomic number tells you the number of
protons in the nucleus
• Each type of atom has a different atomic
number and is a different element
• As of 2011, there are 118 elements.
• While the proton # determines the element,
each element can have varying #’s of
neutrons. These are called isotopes
Examples of Isotopes
Examples of Isotopes
Chemical Bonds
• Electrons are organized into layers called shells
surrounding the nucleus
• The first shell can hold 2 electrons, the second
shell can hold 8, and all additional shells can hold
8 electrons in the outer shell
• Atoms that have 8 electrons in their outer shell
are stable and normally do not form bonds
• Atoms that do not have 8 electrons in their outer
shell will form chemical bonds with other atoms
to fill their outer shell and become stable
Examples of Stable Atoms
Ionic Bonds
• An atom may steal an electron from another to
fill its outer shell.
• The atom that loses the electron also ends up
with a full outer shell
• The atom that stole the electon now has more
electrons than protons and becomes a negatively
charged ion
• The atom that lost the electron now has more
protons than electrons and becomes a positively
charged ion
• Both atoms are attracted and bond to each other
because of their opposite charges
Examples of Ionic Bonds
9P
9P
3P
3P
Examples of Ionic Bonds
Covalent Bonds
• Two atoms may share electrons in their outer
in order to fill their outer shell - remember:
2 electrons in the first shell and
8 in all others
Examples of Covalent Bonds
Hydrogen now has a full
outer shell: 2 electrons
Chlorine now has a full outer
shell: 8 electrons
Water forms through covalent bonds
Oxygen has 6 electrons in
How many hydrogen atoms
its outer shell.
does oxygen need to share
Hydrogen has one electron
How many more does it
in its outer shell.
need
with to fill its outer shell? to be stable?
How many more does it
need to be stable?