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Questions and Answers
What is the general trend for ionic size as you move along a period in the periodic table?
Which property increases from left to right across a period in the periodic table?
What is the main reason behind atoms gaining or losing electrons based on their valence shell configuration?
In which direction does the atomic radius generally increase in the periodic table?
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What happens to the electronegativity of an atom as its valence shell becomes less than half full?
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Which element property tends to increase as you move down a group in the periodic table?
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What happens to ionization energy as you go down a group in the periodic table?
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How does the atomic radius change as you move down a column in the periodic table?
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What is an ionic radius?
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Which group of elements in Mendeleev's original periodic table have partially filled d orbitals?
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What trend applies to metallic character as you move down a column in the periodic table?
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What factor leads to an increase in electron affinity moving down a column in the periodic table?
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Study Notes
Periodic Properties and Variables
The Periodic Law, established by Dmitri Mendeleev in 1869, states that the chemical properties of elements are a periodic function of their atomic weight or atomic number. Mendeleev noticed that when elements were arranged in order of their atomic masses, the properties of the elements repeated themselves in regular intervals, leading him to the idea that elements could be classified based on their atomic numbers instead of atomic weights.
There are several periodic trends related to the properties of elements:
- Electron Configuration: All elements prefer an octet formation consisting of 8 electrons in their valence shell. This leads to the gaining or losing of electrons to achieve stable octet formation.
- Ionic Size: The periodic table shows a gradual increase in the size of the atoms as you move along a horizontal row (period) and a decrease in size going down a vertical column (group).
- Reduction Potential (Electropositivity): The ease with which an atom or ion gives up an electron, indicated by a positive reduction potential, increases from left to right across a period.
- Electronegativity: Atoms tend to gain electrons if their valence shell is less than half full and lose electrons if it is more than half full. Electronegativity measures an atom's tendency to attract and form bonds with electrons. It generally increases from left to right across a period, with elements on the left side of the periodic table having less than a half-full valence shell, requiring less energy to lose an electron than to gain one.
- Ionization Energy: The energy required to remove the most loosely bound outermost electron (first ionization energy) decreases going down a group in the periodic table. This is because as you go down a group, the number of filled principal energy levels (which shield the outermost electrons from attraction to protons) increases, reducing the effective nuclear charge and making it easier for the atom to give up an electron.
- Electron Affinity: The energy released when an element gains an electron increases moving down a column in the periodic table. This is because as you move down a column, the size of the atoms increases, allowing them to accommodate additional electrons with low energy input.
- Metallic Character: Moving down a column in the periodic table, the metallic character increases due to the increasing ability of elements to lose electrons.
Atomic Radius
Atomic radius cannot be directly measured since there is never a zero probability of finding an electron within the atom. However, we can measure the distance between two nuclei, which provides us with information about atomic radii:
- A covalent radius is one-half the distance between the nuclei of two identical atoms.
- An ionic radius is one-half the distance between the nuclei of two ions in an ionic bond.
- A metallic radius is one-half the distance between the nuclei of two adjacent atoms in a crystalline structure.
The noble gases are often excluded from trends in atomic radii due to disagreement over experimental values.
Periodic Table Groups
In Mendeleev's original periodic table, the elements were categorized into groups based on their properties:
- Main group elements: Elements in groups 1, 2, and 13 through 18, which contain the most naturally abundant elements and are essential for life.
- Transition metals: These are found in groups 11 to 17 and have partially filled d orbitals, resulting in variable oxidation states.
- Inner transition metals: Located at z=58, these elements include lanthanides (z=59 to 71) and actinides (z=89 to 103). They are highly radioactive and not often encountered in nature or industry due to their instability.
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Description
Learn about the Periodic Law, periodic trends, and atomic radii measurements. Explore topics like electron configuration, ionic size, electronegativity, and more based on Mendeleev's original periodic table classification.
