Classification of Elements 5 Flashcards
What is oxidation state
the oxidation state of an element in a particular compound can be defined as the charge acquired by its atom on the basis of electronegative consideration from other atoms in the molecule
Who exhibit variable valence
There are many elements which exhibit variable valence. This is particularly characteristic of transition elements and actinoids
The first element of each of the groups 1 (lithium) and 2 (beryllium) and groups 13-17 (boron to fluorine) differs in many respects from the other members of their respective group. Explain.
The first element of each of the groups 1 (lithium) and 2 (beryllium) and groups 13-17 (boron to fluorine) differs in many respects from the other members of their respective group. For example, lithium unlike other alkali metals, and beryllium unlike other alkaline earth metals, form compounds with pronounced covalent character; the other members of these groups predominantly form ionic compounds.
What is the diagonal relationship in the periodic table
Some elements in the 2nd period areresemble much in properties to the elements in the 3rd period of the 2nd group. Ie they are diagonally related in properties
What are the reasons for the different chemical behaviour of the first member of a group of elements in the s- and p-blocks compared to that of the subsequent members in the same group?
The anomalous behaviour is attributed to their small size, large charge/ radius ratio and high electronegativity of the elements. In addition, the first member of group has only four valence orbitals (2s and 2p) available for bonding, whereas the second member of the groups have nine valence orbitals (3s, 3p, 3d). As a consequence of this, the maximum covalency of the first member of each group is 4 (e.g., boron can only form
[BF4 ]− , whereas the other members
of the groups can expand their valence shell to accommodate more than four pairs of electrons
e.g., aluminium AlF 3− forms). [6]
Furthermore, the first member of p-block elements displays greater ability to form pπ – pπ multiple bonds toitself(e.g.,C=C,C≡C, N=N, N ≡ Ν) and to other second period elements (e.g., C = O, C = N, C ≡ N, N = O) compared to subsequent members of the same group.
is it easy to measure atomic radii ? no why
Firstly, because the size of an atom
(~ 1.2 Å i.e., 1.2 × 10–10 m in radius) is very
small. Secondly, since the electron cloud
surrounding the atom does not have a sharp
boundary, the determination of the atomic size
cannot be precise.
Atomic radii
can be measured by X-ray or other
spectroscopic methods.
what is covalent radiii
size of an atom of a non-metallic element is to
measure the distance between two atoms when
they are bound together by a single bond in a
covalent molecule and from this value, the
“Covalent Radius”
what is metallic radi
For metals, we define the
term “Metallic Radius” which is taken as half
the internuclear distance separating the metal
cores in the metallic crystal.
what is van der waal’s radius
Ut is half the distance between nuclei of two non bonded identical isolated atoms or adjacent atoms of neighbouring molecules of an element (usually solid state)
how does atomic radius vary across a period
The atomic size generally
decreases across a period as illustrated in
Fig. 3.4(a) for the elements of the second period.
It is because within the period the outer
electrons are in the same valence shell and the
effective nuclear charge increases as the atomic
number increases resulting in the increased
attraction of electrons to the nucleus.
how does atomic radius vary down a group
increased
attraction of electrons to the nucleus. Within a
family or vertical column of the periodic table,
the atomic radius increases regularly with
atomic number as illustrated in Fig. 3.4(b). For
alkali metals and halogens, as we descend the
groups, the principal quantum number (n)
increases and the valence electrons are farther
from the nucleus. This happens because the
inner energy levels are filled with electrons,
which serve to shield the outer electrons from
the pull of the nucleus. Consequently the size
of the atom increases as reflected in the atomic
radii.
how is atomic radius of noble gases observed?
We use van der waal’s radius for noble gase elements.
Being monoatomic,
their (non-bonded radii) values are very large.
In fact radii of noble gases should be compared
not with the covalent radii but with the van der
Waals radii of other elements.
