in this video we're going to discuss the periodic properties related to valence electrons
metallic character and ionization energy
the first thing we're going to discuss is valence electrons
valence electrons are the electrons on the highest energy level of an atom
so if we look at the periodic table the first thing we can tell
the first thing to notice is the group numbers
group numbers are designated either with just numbers as in 1 through 18
or we have a lettering system as well so we have the 1a 2a
3a through 8a
and then in the middle here we have our B elements which are our transition metals
I tend to use the AB lettering system because it differentiates between the
representative elements that tend to follow the rules
in the transition metals are elements that tend not to follow the rules
so for our representative elements, the A groups
whatever the group number is
that's how many valence electrons are in that specific atom
so carbon for example is in group 4 A
carbon is in group 4 A, has four valence electrons okay, magnesium is in group 2 A
it'll have 2 valence electrons
now...that does not work for the B elements
you can't tell how many valence electrons a group B element has just by it's group number
so if we look at nickel for example
its group number is 8 B
it does not have 8 valence electrons but I'm gonna show you how you can use electron configurations
to determine the number of valence electrons
so for nickle, it ends in 3 D 8
so we're going to write the electron configuration for that element
1s2; 2s2; 2p6; 3s2; 3p6; 3s2; 3p6; 4s2; 3d8
so that would be the electron configuration for nickel
we need to find the highest energy level
the energy levels are designated by the numbers
so 4 would be the highest energy level
on the 4th energy level we have two electrons, so that means that nickle
has two valance electrons
using electron configurations will work for the representative elements as well
if you want to choose an element from the periodic table like oxygen
oxygen has 8 total electrons
based on its group number we would expect it to have six valence electrons
when we do the electron configuration for oxygen
we have 8 electrons total, the highest energy level is 2
on the second energy level we have electrons in the s sub level and the p
so we would have to add them up so that means we have a total of six valence electrons for oxygen
which matches the group number, so you can use electron configuration for either group A or group B elements
for group A elements you can refer to the periodic table and just look at the group number
so the valence electrons are the electrons on the highest energy level
they're going to be the ones that are associated with bonding and the reactivity of the atom
and so those are the ones that we need to focus on when we start looking into bonding
other periodic properties that we can look at...
...metallic character is one of them
and basically metals tend to be shiny
good conductors of heat and electricity
they tend to be ductile and malleable elements
so the more metallic characteristics an atom has
the more metal like it is
metallic character increases going down a group so as you go down the group
with have the least metallic character at the top
and it increases going down in terms of metallic character it's going to
decrease as we go across the periodic table
as you recall nonmetals our own the right side of the periodic table
your medals are on the left side on the periodic table so as we go across from left to right
we start with metals and then they change into metalloids
into non-metals, so the metallic character is going to decrease as you go across the periodic table from left to right
another periodic trend that we can look at is size radius of the atoms
in terms of size this periodic table shows the atomic radius of the elements
as we go down a group or vertical column the size gets larger
we start with level one, we only have one level of electrons, on level two we have two
3...4...5... they get larger and larger
going across from left to right however
you'll notice that they start out large and they start getting smaller and smaller
even though the atomic numbers are increasing which means
more protons in the nucleus and more electrons outside the nucleus
there is actually a greater attraction between the electrons outside the nucleus and the protons in the nucleus
and the atom tends to compress a little bit and it gets a little bit smaller
so if we look at sodium for example has an atomic radius of 166 picometers
and if we go to the other end of the period we have argon which has an atomic radius of 106 picometers
so there's a decrease their from 166 to 106 picometers
so that trend is the same across each row the periodic table
so we can use the periodic table to identify the number of valence electrons
we can also use it to compare the metallic character and the atomic radius of atoms on the periodic table