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).