Atomic Symbol: A unique symbol
used to represent the element in formulas
Atomic Number: Tells you both the number of protons
(p+) and electrons (e-)
Mass Number: Tells you the average atomic mass of an
element. To find this average scientists had to find
the mass of each isotope and their natural abundances
Elements come in different types called isotopes that differ based
on the number of neutrons they contain. Each isotope has its own
precise, whole number mass number:
The mass number of an isotope minus the atomic number
tells you the number of neutrons (no) in
that isotope
Isotopes of an element have slightly different
properties: Carbon-14 is radioactive while the more
common Carbon-12 is not
Groups and Properties
The properties of elements follow the periodic law:
physical and chemical properties are functions of
their atomic numbers.
This follows from similarities between electron
configuration within groups
Hydrogen doesn’t fit into any group because its
simple structure gives it unique properties
Group 1, the Alkali Metals, all have 1 electron in
their outermost s orbital. They ionize to have a +1
charge by losing the s e-
The alkali metals violently replace hydrogen in
water to make a basic (alkaline) solution and are
generally very reactive
Soft and can be cut with a knife
Good conductors of electricity
Group 2, the Alkaline Earth Metals, all have 2
e- in their outermost s orbital. They
ionize to have a +2 charge by losing both their s
e-
Harder, denser and have higher melting points
than the alkali metals
Less reactive than the alkali metals because it
takes more energy to remove 2 e- than
to remove 1
Group 3 through Group 12, the Transition Metals, fill
up the d orbitals and their properties change
very gradually from reactive metals at the left to
less reactive metals at the right side of the family
Except for mercury (Hg), which is a liquid, the
transition metals are harder and denser than the
first two groups
They are all conductors of electricity, though
slightly less conductive as you move toward the
right
The ions that metals form are very variable
although all of them tend to form positively
charged ions by losing 1 or more e-
The lanthanides and actinides are separated from
the main body of the periodic table because they
fill the f orbitals and because they do
not follow the same patterns of periodicity as
the other transition metals
The Main Block elements show the greatest variation
of any of the groups in the periodic table
There are four types of elements in these groups:
metalloids, non-metals, halogens, and the noble
gases
Metalloids represent a 'border' between metals
and non-metals since they have properties of both
The solid non-metals are characterized by their
brittle properties and their lack of conductivity
The halogens are particularly reactive and have a
strong tendency to gain an electron to obtain the
electron configuration of the neighboring noble
gas
The halogens are very often found in combination
with the alkali metals as salts
The noble gases are the elements that have the
most stable electron configurations, having
completely filled out shells
Periodic Trends
Atomic radius: For groups 1
and 2 and groups 13 through 18 atomic radius
increases toward the bottom of the table and
decreases toward the right
Atomic size: this follows the same trend as atomic
radius and can be explained by noting that
e- are drawn closer to the nucleus as
protons are added
Ionization energy: the energy required to remove one
electron increases from left to right and decreases
from top to bottom
Electron affinity: the energy released when an
electron is added to an atom, making it a negative
ion, increases from left to right and decreases from
top to bottom
Electronegativity: this tendency to attract electrons
from another atom in a chemical bond increases as you
move to the right and decreases from top to bottom;
cesium (Cs) is the least electronegative element and
flourine (F) is the most electronegative element
Each isotope has its own
precise, whole number mass number: