Transcript Periodic Trends

Student will learn:
4 periodic trends :
atomic radii trend
ionization trend
electronegativity trend
reactivity trend
Periodic Trends
Atomic Radius
½ distance between nuclei of
identical atoms that are bonded
Ionization Energy
Energy required to remove
one electron
Electronegativity
Atom’s ability to gain an electron.
Reactivity
Atomic Radii
Period trends
Trend to larger radii
because proton pull is less
on e- of same energy level
Group trends
Trend to larger atoms
because e- are added to
NEXT energy level …
farther away from nucleus.
Which has largest atomic radii? Mg, Cl, Na, P,
Which has largest atomic radii?
Ca, Be, Ba, Sr?
Which has smallest atomic radii? Li, O, C, F ?
88888
Octet rule
• Chemical compounds tend to form so that each
atom has an octet of electrons in its highest
occupied energy level. …
• ….atoms will try to get a group of
8 electrons in its outer orbit….
• Either by gaining,
losing,
sharing electrons
Ion =
an atom or group of bonded
atoms that have a + or – charge.
lost an electron = postive……Na+ cation
gain an electron =negative…Cl•
Do oxidation numbers here
anion.
Radii of Ions
Positive Cations lost e- ….
» Lost therefore radii smaller
Negative Anion gained e- ….
» gained therefore radii larger.
Describe the ion radii of the following as
increase or decrease.
Cl,
N,
Ca,
Cu, S,
Na,
Ionization energy
energy required to remove one electron
energy required to make it a cation
Period trends
Increases across
period because more
protons pull greater on
e- in same energy level
Group trends
Increases going
up group. Electrons are closer to
nucleus so protons pull electrons
Tighter therefore takes more energy
to take an e-.
Measured in
k/joules
1st Ionization = energy required to remove 1st electron.
2nd ionization = energy required to remove 2nd electron.
3rd ionization = energy required to remove 3rd electron.
“numbers will increase”
“Arrange the following in increasing ionization energy.”
Li, O, C, K, Ne, F
K,Li,C,O,F,Ne
Be, Ba,Ca,Mg
Ba,Ca,Mg,Be
Which would least likely form?
Sr2+, Al3+, K2+
K2+
Electronegativity
ability to gain electrons ability to become an anion
Period: increases
across period b/c
octet rule is being filled
Group: increases going
up b/c electron closer
to pull of protons
Which element would gain e- easier?
Br, I, Cl, F
Which element is most electronegative?
C, N, O, Se, S
• Reactivity
Which would react easier with chlorine?
Na or K
How about Sodium and Magnesium?
If Li and K and Br were mixed in a beaker. What
compound would be the largest percentage?
1. In a given group lowest first ionization energy is
a.
Noble gas
b. Halogens
c.
Alkali metal
d. Alkaline earth metals
2.
a.
b.
c.
d.
Which element has an ion with a radius
that is larger than its atomic radius?
K
Cr
Zn
Cl
3.Which element in period 3 has the greatest
tendancy to gain electrons?
a.
Ar
b. Cl
c.
Si
d. Na
4.
a.
b.
c.
d.
Arrange the following in
increasing order of atomic radii.
Al, Si, P
Li, Na, K
I, Br, Cl
N, O, F
5.
a.
b.
c.
d.
Which particle has the smallest radii?
Na
K
Na+
K+
6.
Which element would be the most reactive
with water?
Au
Mg
Fe
Na
a.
b.
c.
d.
Student will learn:
4 periodic trends :
atomic radii trend
ionization trend
electronegativity trend
reactivity trend