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A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus.
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons.Carbon Isotopes are shown in the slide.
Slide below shows the isotopes of hydrogen.
Valency of an element is determined by the number of valence electrons present in the outermost shell of its atom.
The atomic size of a chemical element is a measure of the size of its atoms, usually the mean or typical distance from the nucleus to the boundary of the surrounding cloud of electrons.
Elements can be classified into metals and non-metals.
Difference between metals and non-metals.
Johann Wolfgang Döbereiner was a German chemist who arranged the elements with similar properties into groups.
According to Döbereiner in certain triads(groups of three elements) the atomic mass of the central element was merely the arithmetic mean of the atomic masses of the other two elements.
John Newlands was an English scientist who arranged the then known elements in the order of increasing atomic masses.
Newland arranged the then known elements in the order of increasing atomic masses.
Newland arranged the elements in Octaves.
Dmitri Ivanovich Mendeleev was a Russian chemist and inventor. He is credited as being the creator of the first version of the periodic table of elements.
Slide below shows the Mendeleev's Periodic Table.According to Mendeleev the properties of elements are the periodic function of their atomic masses.
Trends of periodic table are shown in the slide.
Mendeleev’s Periodic Table contains vertical columns called ‘groups’ and horizontal rows called ‘periods’.
The Modern Periodic Table has 18 vertical columns known as ‘groups’ and 7 horizontal rows known as ‘periods’.
Noble gases are a group of chemical elements with very similar properties.
Slide shows the place of noble gases in periodic table.
The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn).