يوليو, 2018

 

Electron affinity

Electron affinity

It is the amount of energy given out when an electron is added to a neutral gaseous atom. This results in the formation of an anion.

For example Cl + e– → Cl + energy. The electron affinity of chlorine is 348 kJ mol-1.

Electron affinity changes across a period. The electron affinity of the atoms increases from left to right along a period…

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ملخص الفصل الرابع :أنواع التفاعلات الكيميائية و العلاقات الكمية للمحاليل من كتاب الكيمياء للعالم زومدال Chapter 4 notes: Types of Chemical Reactions and Solution Stoichiometry , Chemistry Zumdahl

ملخص الفصل الرابع :أنواع التفاعلات الكيميائية و العلاقات الكمية للمحاليل من كتاب الكيمياء للعالم زومدال Chapter 4 notes: Types of Chemical Reactions and Solution Stoichiometry , Chemistry Zumdahl

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Four blocks of elements in the periodic table

Four blocks of elements in the periodic table.

1 –  s block elements. Elements of groups 1 and 2 each possessing one and two electrons respectively in the  s orbital of their outermost orbits are together known as  s block elements.

Example :                 Na:  1s2 2s2 2p6 3s1                   Mg:  1s2 2s2 2p6 3s2

Characteristics of s block elements.

a -They are metallic in nature…

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Ionization energy

Ionization energy

(or potential) of an element is defined as “The amount of energy required or needed to remove an electron from the neutral gaseous atom to form unipositive ion , for example Na → Na+ + e– + energy

This is measured in electron volts per atom or kJ mol-1. For example IE of Na is 495 kJ mol-1.

Trends in ionization energy of elements.

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Characteristics of periods and groups of a periodic table

Characteristics of periods and groups of a periodic table

Characteristics of periods

1 –  Valence electrons. On moving from left to right in a period, the number of valence electrons increases from 1 to 8 (except first period where the increase is from one to two only).

  Na         Mg         Al          Si            P           S           Cl          Ar

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Long form or Modern form of periodic table

Long form or Modern form of periodic table

The modem form of period table is based on increasing order of atomic number. General features of the table is as follows:

1 –  There are 18 vertical columns which arc called groups. They are numbered in the old form by IA, IB, IIA, IIB, … VIIA, VIIB VIII and 0 (zero) and in the new…

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Shapes  of s and p orbitals

Shapes  of s and p orbitals

s orbital can have only one possible orientation (as it’s m quantum is zero), it is spherical in shape i.e., in an s orbital the electron distribution is symmetrical around the nucleus in all directions. However the size of s orbital depends on principal quantum number. Large n means large size. Thus 3s orbital is larger than 2s orbital.

There…

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Mendeleev’s periodic law

Mendeleev’s periodic law

Mendeleev gave a periodic law in 1869. According to Mendeleev’s periodic law, the properties, of elements are periodic functions of their atomic masses. He found that if the elements are arranged in the order of increasing atomic masses, then the properties of elements are repeated after regular intervals or periods.

Important features of Mendeleev’s periodic table:

1 – The table…

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Newland’s Law of Octaves

Newland’s Law of Octaves

In 1866 Newland found that when elements are arranged according to increasing atomic masses, the properties of the eight element (starting from a given one) are repetition of the properties of the first element. If we start from lithium (Li) we find that the eighth element from it is sodium (Na). So according to Newland the properties of eighth element, sodium should be…

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Dobereinier’s law of tirade

Dobereinier’s law of tirade

In 1817 Dobereiner found that when elements are arranged in the order of increasing atomic masses, groups of three elements (known as triads) having similar chemical properties are obtained. The atomic mass of the middle element was found to be the average of the rest of the two :

 

Li                  Na                  K

7                   23                  39

Na = (7 +…

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