Organic Chemistry
Trends in the Periodic table
March 24, 2013
Four trends that will be covered:
Atomic size
Ionization Energy
Electronegativity
Electron Affinity
Each of these has a group trend and a period trend
A group trend refers to what is happening with the atom as you travel up or down a column of the periodic table.
A period trend refers to what is happening with the atom as you move left or right across a row of the periodic table
Atomic Size
When discussing an atom’s size, usually the size being referred to is the radius. An atom’s radius is measured from the centre of the atom’s nucleus to its outermost electron shell. Atoms that have more electrons (which will have more electron shells) will have a greater atomic size. An atom with more electron shells is said to have an increased shielding.
Example:
Potassium (K) is larger than hydrogen (H). This is because potassium has 4 electron shells, whereas hydrogen only has 1 electron shell. An alternate way of explaining potassium’s larger size is to say, “Potassium has a greater shielding than hydrogen”.
The period trend for atomic size is that it decreases across the periodic table, from left to right. Sodium is larger than chlorine. This is because of the attractive forces exerted by the protons in the atom’s nucleus. An atom with a greater number of protons in its nucleus will exert a greater attractive force. Since chlorine has 17 protons in its nucleus, and sodium only has 11, chlorines protons will exert a greater attractive force. Therefore, the protons pull its electron shells close in to the nucleus making the atom smaller in size.
Ionization Energy
An atom’s ionization energy is the amount of energy required to remove one electron from that atom. The electron that is removed from the atom would be taken from the outermost electron shell of the atom.
The group trend for ionization energy is that it decreases as you move from the top of the periodic table to the bottom.
March 24, 2013
Four trends that will be covered:
Atomic size
Ionization Energy
Electronegativity
Electron Affinity
Each of these has a group trend and a period trend
A group trend refers to what is happening with the atom as you travel up or down a column of the periodic table.
A period trend refers to what is happening with the atom as you move left or right across a row of the periodic table
Atomic Size
When discussing an atom’s size, usually the size being referred to is the radius. An atom’s radius is measured from the centre of the atom’s nucleus to its outermost electron shell. Atoms that have more electrons (which will have more electron shells) will have a greater atomic size. An atom with more electron shells is said to have an increased shielding.
Example:
Potassium (K) is larger than hydrogen (H). This is because potassium has 4 electron shells, whereas hydrogen only has 1 electron shell. An alternate way of explaining potassium’s larger size is to say, “Potassium has a greater shielding than hydrogen”.
The period trend for atomic size is that it decreases across the periodic table, from left to right. Sodium is larger than chlorine. This is because of the attractive forces exerted by the protons in the atom’s nucleus. An atom with a greater number of protons in its nucleus will exert a greater attractive force. Since chlorine has 17 protons in its nucleus, and sodium only has 11, chlorines protons will exert a greater attractive force. Therefore, the protons pull its electron shells close in to the nucleus making the atom smaller in size.
Ionization Energy
An atom’s ionization energy is the amount of energy required to remove one electron from that atom. The electron that is removed from the atom would be taken from the outermost electron shell of the atom.
The group trend for ionization energy is that it decreases as you move from the top of the periodic table to the bottom.