This site is instructive and gives new STEM understudies the materials for subjects they will require in the school year.
There are on the whole scientific and literary material. There are for the most part books, references, questions, and many documents such as PPT., DOCX., and PDF., which additionally contain clarifications.
-When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.
Horizontal rows = periods
There are 7 periods
-Vertical column = group (or family)
Similar physical & chemical prop.
Identified by number & letter (IA, IIA)
Trends and Periodicity.
-Periodic trends are specific patterns that are present in the periodic
table that illustrates different aspects of a certain element, including its size and its electronic properties.
-Major periodic trends include
electronegativity, ionization energy, electron affinity, atomic radius, melting point, and metallic character. Periodic trends, arising from the arrangement of the periodic table, provide chemists with an invaluable tool to quickly predict an element's properties.
-These trends exist because of the similar atomic structure of the
elements within their respective group families or periods, and because of the periodic nature of the elements.
Atomic Radius.
Atomic radii is useful for determining many aspects of chemistry such as various physical and chemical properties. The periodic table greatly assists in determining atomic radius and presents a number of trends.
-Definition
Atomic radius is generally stated as being the total distance from an atom’s nucleus to the outermost orbital of electron. In simpler terms, it can be defined as something similar to the radius of a circle, where the center of the circle is the nucleus, and the outer edge of the circle is the outermost orbital of electron. As you begin to move across or down the periodic table, trends emerge that help explain how atomic radii change.
Types of Radius with Respect to Types of Bonds
Covalent Radius
Ionic Radius
Metallic Radius
-Vertical Trend
The radius of atoms increases as you go down a certain group.
-Horizontal Trend
The size of an atom will decrease as you move from left to the right of a period.
Ionization Energy
-Definition
Ionization energy is the quantity of energy that an isolated, gaseous atom in the ground electronic state must absorb to discharge an electron, resulting in a cation.
-This energy is usually expressed in kJ/mol, or the amount of energy it takes for all the atoms in a mole to lose one electron each.
Electronegativity
-Definition
Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to cesium and francium which are the least electronegative at 0.7.
-Summary
No electronegativity difference between two atoms leads to a pure non-polar covalent bond.
A small electronegativity difference leads to a polar covalent bond.
A large electronegativity difference leads to an ionic bond.
Electron Affinity
-Definition
Electron affinity is defined as the change in energy (in kJ/mole) of a neutral atom (in the gaseous phase) when an electron is added to the atom to form a negative ion. In other words, the neutral atom's likelihood of gaining an electron.
Nonmetals vs. Metals
To summarize the difference between the electron affinity of metals and nonmetals :
-Metals:
Metals like to lose valence electrons to form cations to have a fully stable octet. They absorb energy (endothermic) to lose electrons. The electron affinity of metals is lower than that of nonmetals.
-Nonmetals:
Nonmetals like to gain electrons to form anions to have a fully stable octet. They release energy (exothermic) to gain electrons to form an anion; thus, electron affinity of nonmetals is higher than that of metals
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