Transcript Ch. 6.3

 Size
is expressed in terms of atomic radius.
 Atomic radius is ½ the distance between the
nuclei of two atoms of the same element
when the atoms are joined.
 In general, atomic radius increases from top
to bottom within a group and decreases from
left to right across a period.
 Two
changes as atomic number increases as
you go down a group…
 The charge on the nucleus increases, drawing
electrons and closer to the nucleus, and…
 The number of occupied energy levels
increases, with occupied orbitals shielding
electrons in the highest occupied energy
level from the attraction of protons in the
nucleus.
 The
shielding effect is greater than the
attractive force of the nucleus, so atomic
size increases.
 Within
a period, size decreases from left to
right.
 As protons are added across the period, the
electrons in the same principal energy level
are pulled closer to the nucleus.
 Since the shielding effect is constant for all
elements in a period, atomic size decreases
across the period.
 An
ion is an atom or group of atoms that has
a positive or negative charge.
 Atoms are electrically neutral ….the number
of protons equals the number of electrons.
 Positive and negative ions form when
electrons are transferred between atoms.
 A cation is a positively charged ion. It has
lost one or more electrons, so it has more
protons than electrons, and a net positive
charge. Na1+
 An
anion is a negatively charged ion. It has
gained one or more electrons. With more
electrons than protons, it has a negative
charge. Cl1-
 Ionization
energy is the energy required
(measured in the gaseous state) to remove
an electron from an atom.
 The energy required to remove the first
electron from an atom, forming a cation with
a 1+ charge, is called the first ionization
energy.
 First ionization energy tends to decrease
from top to bottom within a group, and
increase from left to right across a period.
 First
ionization energy generally decreases
from top to bottom within a group.
 Since atomic size increases down the group,
the nucleus’ charge has a smaller effect on
the electrons in the highest occupied energy
level.
 First
ionization energy generally increases
from left to right across a period.
 As the nuclear charge increases, the
shielding effect remains constant. The
electrons have a greater attraction for the
nucleus, so it takes more energy to remove
an electron from an atom.
 Cations
are always smaller than the atoms
from which they are formed.
 Anions are always larger than the atoms
from which they are formed.
 Electrons
are involved in the bonding of ions
to form compounds.
 Electronegativity is the ability of an atom of
an element to attract electrons when the
atom is in a compound.
 In general, electronegativity values
decreases from top to bottom within a
group, and, for representative elements, the
values tend to increase from left to right
across a period.
 The
least electronegative element is cesium,
with the least tendency to attract electrons
(0.7).
 The most electronegative element is fluorine
(4.0).