Chapter 1Chapter 1
Activity 6: Atoms with More than one Electron
PERIODICITY There are general trends in
the properties of atoms and their ions with increasing atomic number.
These trends can be explained using the periodic table.
PERIODICITY Can you name a trend that we have
talked about this year? Think about what you graphed
Atomic Mass vs Atomic # As Atomic # increases, Atomic Mass
increases
Atomic Radius vs Atomic # As Atomic # increases, Atomic Radius
increases down a group, but decreases across a period.
Atomic Radius vs Atomic NumberA
tom
ic R
ad
ius
(pm
)
Atomic Number(protons)
Period Trend
As you proceed from left to right across a row (period), the atomic radius decreases (the atoms get smaller).
Why????
Period
The period # indicates how many energy levels the atoms in that period have.
Notice the increasing number of protons….
SO….as the number of protons increases, the outer electrons are pulled in closer to the nucleus and the
atomic radius gets smaller!
Atomic Radius vs Atomic NumberA
tom
ic R
adiu
s(p
m)
Atomic Number (protons)
Group Trend
As you proceed down a group (family or column), the atomic radius increases (the atoms get larger).
Why???
The period # indicates how many energy
levels the atoms in that period
have.
H
Li
Na
K
So…As you proceed down a group, the number of energy levels increases. This increases the atomic radii of the atoms.
Row 1
Row 2
Row 3
Row 4
http://www.youtube.com/watch?v=xjEJl88AYMohttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/atomic4.swf
Which atom is larger, Al or Si? Why????
Which atom is smaller, Br or I? Why????
Background Electrons can move between energy levels
(Bohr’s model supported by line spectra)
The nucleus and electrons are attracted to each other (opposites attract)
Electrons that are far away from the nucleus can escape the attraction of the nucleus (atoms can lose electrons)
Losing an electron is called ionization
Ionization Energy
Ionization energy is the energy required to remove a valence electron from an atom.
Valence electron= outermost electron that is farthest from the nucleus.
group
period
Ionization energy vs. atomic numberIonization energy vs. atomic number
Ca
K
H
He
Li
B
Be C
N O
F
Ne
Na
MgAl
SiP S
Cl
Ar
0
500
1000
1500
2000
2500
0 2 4 6 8 10 12 14 16 18 20
Atomic Number (# of protons)
Ioni
zatio
n en
ergy
(kJ/
mol
)
Ionization Energy in kJ/mol
D
I
Ionization Energy
D
Energy needed to remove a loosely held electron from an atom
Decreases as you move down a group
Atom gets bigger, more energy levels
Nucleus is further from the outer most electron (valence electrons)
Nucleus & electron attraction decreases, so it is easier to take an electron away.
Ionization Energy
I
D
Energy needed to remove a loosely held electron from an atom
Increases as you move across a period
Nonmetals hold onto their electrons tighter
Atom is smaller, so nucleus is closer to valence electron making it harder to remove.
http://www.youtube.com/watch?v=o6tv03DR_Gg
Ionization Energy
Which has higher ionization energy?
He or Xe? (kJ/mol)
He Xe2372 kJ/mol 1170 kJ/mol
Smaller atom, He holds on tighter to valence electron
Practice
Metals have a low Ionization Energy
want to lose e-s to become stable
NonMetals have a high Ionization Energy
do not want to lose e-s, want to gain e-s
Ionization Energy
Which has higher ionization energy?
Li or Ne? (kJ/mol)
Li Ne520 kJ/mol 2081 kJ/mol
Ne holds onto atoms tighter
Practice