Mendeleev's periodic table was based on his periodic law, which stated that "the physical and chemical properties of elements are a periodic function of their atomic masses." His table contained seven periods and eight groups, but the 0 group (inert gases) was absent. Mendeleev left gaps for elements not known at that time, such as Eka-boron, Eka-aluminium, and Eka-silicon, which were later discovered as scandium, gallium, and germanium, respectively. The table lacked a fixed position for hydrogen, had no space for isotopes, and did not arrange atomic masses regularly, necessitating its modification.
In 1913, Moseley modified Mendeleev’s periodic law and proposed the modern periodic law, stating that "the physical and chemical properties of the elements are a periodic function of their atomic numbers." Moseley discovered that atomic number is a more fundamental property than atomic mass.
Characteristics of Periods:
Characteristics of Groups:
Block Elements:
Elements can be classified into four blocks:
New Super Heavy Element 117Researchers at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany, have created and observed several atoms of element 117, temporarily named ununseptium. In the periodic table, ununseptium is located in group 17. While previous group 17 members are halogens, ununseptium is likely to have significantly different properties, although key properties such as melting point, boiling point, and ionization potential are expected to follow periodic trends.
Periodic properties are characteristics that repeat at regular intervals in the periodic table, displaying a consistent pattern along groups and periods. Some important periodic properties include:
Ionisation Enthalpy: The minimum energy required to remove an electron from an isolated gaseous atom of an element, forming a positive ion. Ionisation enthalpy increases along a period but decreases down a group. Boron and oxygen have lower ionisation energies than beryllium and nitrogen, respectively, due to their stable electronic configurations.
Electron Gain Enthalpy: The energy released when an extra electron is added to a neutral gaseous atom of an element. Electron gain enthalpy increases along a period and decreases down a group, with some exceptions.
Electronegativity: The ability of an atom to attract a shared pair of electrons towards itself. Electronegativity increases along a period and decreases down a group.
Metallic Character: The tendency of an element to form a cation by losing electrons. Metallic character decreases along a period and increases down a group.
Oxidising and Reducing Character: Reducing character decreases along a period and increases down a group, while oxidising character increases along a period and decreases down a group.
Valency: Valency with respect to hydrogen increases from 1 to 7 across a period. With respect to oxygen, it first increases from 1 to 4 and then decreases to 1 (except for OF2). Valency remains the same within a group.
Basic Nature of Oxides: The basic nature of oxides decreases along a period while the acidic nature increases. Conversely, down a group, the basic nature of oxides increases while the acidic nature decreases.
Hydrogen is a non-metal that becomes metallic under very high pressure. It constitutes about 10% of the weight of living organisms and is the most abundant element in the universe, making up 70% of the universe's total mass. In its combined state, hydrogen is the third most abundant element in the Earth's crust. It is a fundamental component of the sun and stars.
Types of Water:
Degree of Hardness
The degree of hardness is defined as the number of parts of CaCO3 or its equivalent in various calcium or magnesium salts present in 106 parts of water by mass.
Heavy Water (D2O):
Discovered by Urey and Washburn in 1932, heavy water is present in a ratio of one part per 6000 parts of ordinary water. It is a colorless, odorless, tasteless liquid with a maximum density of 1.1073 g/mL at 11.6°C. Heavy water has higher physical constants than ordinary water due to the greater nuclear mass of deuterium and stronger hydrogen bonding. Chemically, it reacts more slowly than ordinary water due to the isotopic effect.
Effects of Heavy Water:
Hydrogen Peroxide (H2O2):
Discovered by Thenard, hydrogen peroxide is also known as oxygenated water and is found in trace amounts in the atmosphere, plants, rain, and snow. It decomposes in light and is stored in dark-colored or wax-lined bottles to prevent decomposition.
Uses of Hydrogen Peroxide (30% Perhydrol):
464 videos|571 docs|394 tests
|
1. What are the periodic properties of elements? |
2. What is the significance of hydrogen in the periodic table? |
3. How is the periodic table classified in SSC CGL exams? |
4. What are some common periodic trends tested in SSC CGL exams? |
5. How does the evolution of the periodic table contribute to our understanding of chemical elements? |
|
Explore Courses for SSC CGL exam
|