Transcript Atomic radii - Christopher Dock Mennonite High School

What are the periodic trends?
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Atomic radius
Ionization energy
Affinity
electronegativity
Shielding affect
Atomic radii
• Defined as one-half the distance between
the nuclei of identical atoms that are bonded
together.
• ( draw picture)
Trends
• Radii decreases from left to right across a period.
– Add protons, add p-e pull
• Increases as you go down a family
– Adding energy levels, layers
– Exception Al- Ga
– Table 5-13 page 141
– slide
Questions
• In period 3, which has the largest radius
– Na, Mg, P, Cl
– In family 2 which has the largest radius
• Ca, Be, Ba, Sr
Ionization Energy
• The energy required to remove an electron
from a neutral atom. (first ionization
energy)
• Pg 143 figure 5-15
• When you remove an electron from a
neutral ion you form an ion.
• Any process that results in the formation of
an ion is ionization.
Trends
• Ionization energy increases from left to
right across a period.
– It gets harder and harder to remove an electron
– Radius is smaller, the pull between nucleus and
electron is greater.
– Noble gas – can’t remove the electron.
– Dips where electrons double up in an orbital.
Trends
• Ionization energy generally decreases as
you go down a family.
– The radius is larger, the electrons are further
away and are therefore held less tightly.
– Shielding occurs – there are more energy levels
that have electrons in them, they shield the
outer electrons from the nuclear pull.
– Show slide
Second ionization energy
• The energy required to remove a second
electron from an atom ( ion).
• Always requires more energy to remove the
second and successive electrons than the
first.
• Table 1-3 pg 145
practice
• Element A has a first ionization energy of
419 kJ/mol. Element B has a first ionization
energy of 1000 kJ/mol.
– Are they in the s or p block?
– Which will most likely give up their electron?
Electronegativity
• Measure of the ability of an atom in a
chemical compound to attract electrons.
– Fluorine assigned a number 4
– Everything else is based off of that value.
Trend
• Family 18 exception
• Family 1 is very willing to give up its
electrons.
– Has a noble gas configuration if it does
– Loosely held
• Family 17 wants electrons
– Fill the outer energy level
– Stable
Trend
• As you go left to right across a period it
electronegativity increases
• As you go down a family electronegativity
will decreases
– Shielding affect
– Electrons are further out, loosely held
practice
• Given the elements Ga, Br and Ca which
has the highest electronegativity?
• Given 2s22p5 , 4d105s25p5, and 2s22p2
– Which is the most electronegative?
– Which two are in the same family?
Affinity and Electronegativity
• Both affinity and electronegativity measure
an atom’s ability to attract electrons.
• Affinity is the energy change when an atom
gains an electron
• Electronegativity measures the ability of an
atom to attract electrons.
Electron Affinity
• The energy change that occurs when an electron is
acquired by a neutral atom.
• If energy is released when an atom gains an
electron, the atom is more stable with the extra
electron. This will be represented as a negative
number
– Cl- -361.7 k
• Group 17 gains electrons readily.
affinity
• If energy is required to make the electron
‘stick’, then the atom is less stable.
• This is represented by a positive number for
electron affinity or zero.
Stability
• Atoms will always want the most stable
configuration;
– A noble gas configuration
– A filled sublevel
– A half filled sublevel, 1 electron per orbital.
practice
• Given 2s22p5 , 4d105s25p5, and 2s22p2
Which has the highest electron affinity?
• Which family would you expect to have a
greater electron affinity, family 2 or 16?
trends
• Not as regular as other trends.
• Affinity increases left to right across a
period. (electrons are added more easily)
• Affinity decreases down a family. Electrons
add with greater and greater difficulty as
you go down a family.
– Less nuclear attraction – shielding affect
Ionic radii
• Cation – loss of an electron always causes a
decrease in atomic radius.
• Anion – gain of electrons always increases
atomic radius
Trends
• Table 5-19 page 149
• Ionic radii decreases across a period.
– Cationic radii decreases across a period then in
family 15 radii start to increase.
– Radii increases down a family.
Ion electron configuration
• examples
Valence electrons
• Outer level, highest level electrons.
• Electrons available to be lost, gained, or
shared in the formation of chemical
compounds.
Section review
• State and discuss the general period and group trends among the main
group elements.
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Radius
First ionization energy
Electron affinity
Ionic radius
Electronegativity
• Among the main group elements, what is the relationship between the
group number and the number of valence electrons?
• How do the periodic properties of the d block elements compare with
hose of the main group elements?
Section review
• Among the main group elements,what is the
relationship between the group number and
the number of valence electrons?
• How do the periodic properties of the d
block elements compare with hose of the
main group elements?