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Atom: the smallest part of an element that
maintains the properties of that element
Element: a substance that is composed of one
type of atom
Parts of an Atom:
Proton: positively charged (nucleus)
Electron: negatively charged (electron
cloud)
Neutron: no charge (nucleus)
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The number of protons and electrons in
most atoms are equal giving the atom a net
charge of zero.
Periodic Table – the periodic table of
elements is used to group elements
according to their characteristics. Each
element has a number and a symbol.
Atomic
number
Element symbol
Elemen
t name
Atomic
mass



The atomic number tells you the number of
protons
The atomic mass is equal to the number of
protons + the average number of neutrons
In some atoms, called isotopes there are
more or less neutrons. Isotopes usually have
slightly different properties than their parent
atoms.
Symbol
Nitrogen
Oxygen
Carbon
Atomic
Number
Atomic
Mass
Protons
Neutrons
Electrons
Number of
Protons
Number of
Neutrons
Atomic Mass
Properties
Carbon - 12
6
6
12
Typical
Carbon
Carbon – 14
6
8
14
Radio
isotope, can
be used for
carbon
dating and
as a marker
element

Almost all of the mass of an atom is found in
the nucleus.
◦ Protons and Neutrons are given the same mass
values (1 amu)
◦ AMU = atomic mass unit

If an atom gains or losses electrons, it
becomes an ion
◦ Ions have positive or negative charges
◦ Losing electrons gives an atom a more positive
charge
◦ Gaining electrons gives an atom a more negative
charge
◦ Positively and negatively charged ions are attracted
to one another
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Forces that hold atoms together are called
bonds.
The outermost electrons of an atom
determine its bonding abilities
The different orbits of an atom hold different
numbers of electrons. The first orbit holds
two electrons. Each orbit after that holds 8.
Atoms without full orbits bond readily with
other atoms to fill their orbits


Filling outer orbits stabilizes the atoms and
forms compounds or molecules.
Ionic bonds form between oppositely charged
ions to fill their orbits. One atom loses and
electron and the other atom gains it.


Covalent Bonds form when two or more
atoms share electrons.
Carbon atoms can create bonds with up to
four other atoms, making it a very versatile
atom. It is also able to form double and triple
bonds, which are strong, because they are
sharing two or three electrons.