Download Periodic Trends - Barrington 220

WHAT IS A PERIODIC TREND?
A change that is predictable and repeats
ex: seasons, months, days of the week, school day
Atomic size: Because atoms have no true boundary, atomic radius is used to
measure size
Periodic Trends
ATOMIC RADIUS: one-half of the distance from the nucleus of two like atoms
TREND ACROSS a period (left to right): DECREASES
EXPLANATION: electrons enter the SAME energy level, as protons and electrons are
added the force between the protons and electrons increase. The
electrons are pulled closer to the nucleus making the atom smaller
TREND DOWN a family: INCREASES
EXPLANATION: as electrons are added to more energy levels, the inner layers shield
the outer electrons from the pull of the nucleus. The added electrons
have less attraction to the nucleus due to this shielding effect,
increasing the atom‛s size
Ionic Radius:
• Positive ions are smaller than their neutral atom
• Negative ions are larger than their neutral atom
Oct 10­9:43 AM
Atomic Radius
Ionization Energy
Sep 24­7:50 AM
Electronegativity
decrease
IONIZATION ENERGY: the energy needed to remove the outermost electron from an
atom
TREND ACROSS a period: INCREASES
increase
Pull
Atomic Radius
EXPLANATION: the atom‛s radius decreases, the electrons are held tighter by the
nucleus, so it will take more energy to remove an electron
TREND DOWN a family: DECREASES
EXPLANATION: the atom‛s radius increases, the electrons are held less tightly by the
nucleus, so it will take less energy to remove an electron
Oct 10­9:32 AM
Sep 24­9:24 AM
1
ELECTRONEGATIVITY: the ability of an atom to attract an electron from another atom
Electron affinity: the energy released when adding an electron
Trends Summarized
TREND ACROSS a period(left to right): INCREASES
Atomic Radius
Ionization Energy
Electronegativity
EXPLANATION: the atom‛s radius decreases, the nucleus has a stronger
pull on an extra electron
decrease
increase
increase
increase
decrease
decrease
TREND DOWN a family: DECREASES
EXPLANATION: the atom‛s radius increases, the nucleus has a weaker
hold on an extra electron
Sep 24­9:31 AM
Oct 10­9:21 AM
2