Download Emission Spectrum and Periodic Trends

Trends in the
Periodic Table
Periodicity
Review of Atomic Forces
Atomic Radius
Ionization Energy
Ions are their sizes
Electronegativity
Periodicity
• The word Periodic means recurring at
regular intervals
– The Periodic Table is an organization of the
atoms such that their properties repeat on each
row
• This means that elements in the same group
(column) have similar properties.
• We will learn why elements in the same group have
similar properties and why elements are more or less
reactive depending on which period they are in.
Review of Atomic Forces
• Opposite charges attract and like charges repel
– Increasing protons in the nucleus increases the attraction
of electrons pulling them closer to the nucleus
– Increasing electrons in the electron cloud, increase the
repulsion between the electrons
– The closer electrons are to the nucleus the stronger the
attraction to the nucleus
– Electrons in the same energy level are about the same
distance from the nucleus, electrons in higher energy
levels are farther from the nucleus.
Trends in the Periodic
Table
• Atomic Radius
– The outside edge of the atom is defined by the electron
cloud
– As you move down a group, the size of the atom increases
• the number of energy levels increases making the electron cloud
bigger, so atomic radius increases
– As you move across a period from left to right, the size of the
elements decreases.
• The number of e- increases but the additional e- are on the same
energy level, which does not increase the size of the atom.
• The number of protons in the nucleus increases which means there is
a greater inward attraction of the electrons.
Ionization Energy
• First Ionization Energy – the amount of energy
required to remove the first e- from an atom
– The higher the ionization energy, the harder it is to
remove an e-
• As you move down a group, the ionization energy
decreases (e- are easier to remove from an atom)
– Electrons close to the nucleus are held more tightly
because they are closer to the protons
• As you move down a group the outer e- are farther and farther
away from the nucleus, making them easier to remove
• Electrons in lower energy levels shield the outer energy levels
from the full force of the protons, making outer e- easier to
remove.
– Ionization energy increases as you move across a period
• The number of protons in the nucleus increases which means
there is a greater inward attraction of the e-, making it more
difficult to remove an e-.
Ionization Energy
(Continued)
– Second, Third, and Fourth Ionization Energies
• With each e- removed, it gets harder to remove additional
electrons, because the ratio of protons to electrons increases.
• There are the same number of protons pulling on fewer
electrons.
Electronegativity
• Electronegativity – the ability of an atom to attract
electrons
– A large value indicates that the atom strongly attracts e– If two atoms are fighting over an electron, the atom with
the greater electronegativity will win the battle
• Electronegativity decreases as you move down a
group
• Electrons in higher energy levels are not attracted as strongly
because they are father from the nucleus
• Electrons in lower energy levels shield the outer energy levels
from the full force of the protons
– Electronegativity increases as you move left to right
across a period
• Atoms with more protons tend to have a stronger attraction of e-
6.3
Comprehension Check
• Summary of Trends
– What is the underlying cause of periodic
trends?
6.3
Record on your
Periodic Table
Increases Decreases
Ionization
energy
Nuclear
Electronegativity
Atomic Size
Charge
Decreases
Increases
Comprehension Check
1. Which of the following sequences is correct
for atomic size?
•
•
•
•
Mg > Al > S
Li > Na > K
F>N>B
F > Cl > Br
2. Which of the following is the most
electronegative?
•
•
•
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Cl
Se
Na
I
Other Trends in the
Periodic Table