In 1800, only _____ elements were known.
31
By 1865 AD, the number of identified elements had more than doubled from 1800 AD to _____.
63
Mendeleev's Periodic Table had ____periods and ____groups.
7 periods and 9 groups.
Modern Periodic Table had ____periods and ____groups.
7 periods and 18 groups.
_____________ showed that the atomic number is a more fundamental property of an element than its atomic mass.
Henry Moseley
According to the recommendation of International Union of Pure and Applied Chemistry (IUPAC), the groups are numbered from 1 to 18 replacing the older notation of groups _______________
IA … VIIA, VIII, IB … VIIB and 0.
The first period contains 2 elements. The subsequent periods consists of _,_,__,__,__- elements, respectively.
8, 8, 18, 18 and 32
The _________ period is incomplete.
seventh
Both American and Soviet scientists claimed credit for discovering element 104. The Americans named it _______ whereas Soviets named it _______.
The Americans named it Rutherfordium whereas Soviets named it Kurchatovium
Within a period, chemical reactivity tends to be high in Group _______, lower in elements towards the middle of the table, and increases to a maximum in the Group __________.
high in Group 1 metals,maximum in the Group 17 non-metals
Within a group of representative metals reactivity _________ on moving down the group, whereas within a group of non-metals, reactivity ___________ down the group.
Within a group of representative metals reactivity increases on moving down the group, whereas within a group of non-metals (say halogens), reactivity decreases down the group.
Being monoatomic, Noble gas radii (non-bonded radii) values are very __________.
large
Noble gases radii should be compared not with the covalent radii but with the ________________ of other elements
van der Waals radii
The cation with the greater positive charge will have a _________ radius .
smaller
Anion with the greater negative charge will have the _____radius.
larger
For Alkali metals Low ionization enthalpies can be correlated with _________reactivity.
low ionization enthalpies can be correlated with their high reactivity.
The effective nuclear charge experienced by a valence electron in an atom will be ______ than the actual charge on the nucleus because of “shielding” or “screening” of the valence electron from the nucleus by the intervening core electrons.
less
Across a period, increasing nuclear charge ___________ the shielding.
outweighs
As we go down a group, ____________ in shielding outweighs the increasing nuclear charge
increase
Boron has a ________ first ionization enthalpy than beryllium.
smaller
Nitrogen has a ___________ first ionization enthalpy than oxygen.
larger
Half filled and fully filled orbital are more stable.This is ________rule
Hund's
Group 17 elements (the halogens) have very high __________ electron gain enthalpies
negative
Nble gases have large __________ electron gain enthalpies
positive
Negative of Electron Gain Enthalpy (∆egH) is _____________
ELECTRON AFFINITY (Ae )
If energy is released when an electron is added to an atom, the electron affinity is taken as ____________.
positive
For many elements energy is released when an electron is added to the atom and the electron gain enthalpy is ______.
negative
Electron gain enthalpy of O or F is less negative than that of the ___________ element.
succeeding
Electronegativity is inversely related to the _______ properties of elements.
metallic
A qualitative measure of the ability of an atom in a chemical compound to _______ shared electrons to itself is called electronegativity.
attract
Unlike ionization enthalpy and electron gain enthalpy, it _____ a measureable quantity.
is not
A number of numerical scales of electronegativity of elements viz., _____________
Pauling scale
The one which is the most widely used is the Pauling scale. Linus Pauling, an American scientist, in 1922 assigned arbitrarily a value of _____to fluorine, the element considered to have the __________ ability to attract electrons.
4.0 ,greatest
Electron affinity is defined as absolute zero and, therefore at any other temperature (T) heat capacities of the reactants and the products have to be taken into account in ∆egH = ____________.
–Ae – 5/2 RT
The electronegativity of any given element ____________constant
is not
Metals comprise more than ____________ per cent of the known elements.
seventy eight
Non-metals, which are located at the top of the periodic table, are less than _____________in number.
20
