Enthalpy of fusion is the measure of the energy needed to change a substance from a solid to a liquid. Extra energy is needed, more than what is obvious by the temperature scale. For example, ice at 0°C needs to absorb heat before it converts (changes) to water at 0°C. The temperature does not change, but energy is absorbed to change from solid to liquid.
Ionization energy
Ionization energy is the energy needed to remove the most loosely attached electron from an atom. The atom is not connected to any other atoms. The chemical elements to the left of the periodic table have a much lower ionization energy. The ones to the right have a much higher ionization energy. The chemical elements down the periodic table have a much lower ionization energy (due to electrons being farther away from the atom with increasing atomic radius). The ionization energy increases as each electron is removed.
Ionization energies are dependent upon the" atomic radius". Since going from right to left on the periodic table, the atomic radius increases, and the ionization energy increases from left to right in the periods and up the groups. Exceptions to this trend is observed for alkaline earth metals (group 2) and nitrogen group elements (group 15). Typically, group 2 elements have ionization energy greater than group 13 elements and group 15 elements have greater ionization energy than group 16 elements. Groups 2 and 15 have completely and half-filled electronic configuration respectively, thus, it requires more energy to remove an electron from completely filled orbitals than incompletely filled orbitals.
Alkali metals (IA group) have small ionization energies, especially when compared to halogens or VII A group. In addition to the radius (distance between nucleus and the electrons in outermost orbital), the number of electrons between the nucleus and the electron(s) you're looking at in the outermost shell have an effect on the ionization energy as well. This effect, where the full positive charge of the nucleus is not felt by outer electrons due to the negative charges of inner electrons partially canceling out the positive charge, is called shielding. The more electrons shielding the outer electron shell from the nucleus, the less energy required to expel an electron from said atom. The higher the "shielding effect" the lower the ionization energy. It is because of the shielding effect that the ionization energy decreases from top to bottom within a group. From this trend, Cesium is said to have the lowest ionization energy and Fluorine is said to have the highest ionization energy (with the exception of Helium and Neon).
The "first ionization energy is the" energy required to take away an electron from a neutral atom and the "second ionization energy" is the energy required to take away an electron from an atom with a +1 charge and so on. Each succeeding ionization energy is larger than the preceding energy.
Electron orbitals are separated into various shells which have strong impacts on the ionization energies of the various electrons. For instance, let us look at aluminum. Aluminum is the first element of its period with electrons in the 3p shell. This makes the first ionization energy comparably low to the other elements in the same period, because it only has to get rid of one electron to make a stable 3s shell, the new valence electron shell. However, once you've moved past the first ionization energy into the second ionization energy, there is a large jump in the amount of energy required to expel another electron. This is because you now are trying to take an electron from a fairly stable and full 3s electron shell.
Picometer
A picometer is a measurement. It is one millionth of a billionth of a meter. It is also one trillionth of a millimeter. This is very small. Many atoms are larger than this.
1×10−12 m(1000,000,000,000)
1 E-10 m
To help compare different orders of magnitude this page lists lengths between 10 m and 10 m (100 pm and 1 nm).
Covalent radius
The covalent radius is the radius of an atom that is measured when that atom is in a covalent bond. It is normally measured in picometers. It is normally found by X-ray diffraction.
Van der Waals radius
The Van der Waals radius is the radius of an atom that is seen as a hard sphere. It is named after someone who realized that atoms were not points, but actual objects. It can be found by the critical point and the physical properties of a gas. It also can be found by a molecular crystal.
Diamagnetism
Diamagnetism is a type of magnetism. They very weakly repel magnets. Most substances are diamagnetic. It was discovered in 1778 when someone saw that bismuth and antimony repelled a magnet. Diamagnetic things can be levitated. A frog was levitated in a very strong magnet. Water can be repelled by a magnet because it is diamagnetic. It is too weak to be noticed normally, though.
Young's modulus
Young's modulus is the measure of how much force is needed to stretch or compress a substance. Its most basic form is stress/strain. Stress is the measure of the force applied to a certain area. Strain is the amount by which the substance is deformed.
Shear modulus
Shear modulus is a measure of the amount of force that will shear or twist an object. It is normally the letter "G". It is the measure of the force needed to shear an object that is attached to a solid object. It can also measure the amount of force needed to twist an object.
Bulk modulus
The bulk modulus (letter "K") is a measure of the resistance of a substance to compression on all sides. Gases are easily compressed, while solids and liquid are only compressed with difficulty. It is measured by a measuring instrument when another object is placed under pressure. Its unit is psi.
Poisson's ratio
Poisson's ratio (letter "v") is a measure of the contraction that happens when an object is stretched. It is named after Siméon Denis Poisson. This contraction is perpendicular to the stretching force. It can also expand as the object is compressed in a perpendicular direction.
For example, if a block is being stretched as shown in the image to the right, the equation for the poisson's ratio will be:
Poisson's ratio ranges from 0.0-0.5 for common materials, though for materials with certain structures, can be as low as -1. A material with a Poisson's ratio close to 0 (like cork) can be stretched a lot in the axial direction without changing much at all in the transverse, where as pulling on a material with a high Poisson's ratio (like rubber) will cause it to become much more narrow. A material with a negative Poisson's ratio will expand in all directions as it is stretched.
Brinell scale
The Brinell scale is a measure of hardness in materials. It is measured by making a dent in the material and seeing how deep the dent goes with a known amount of force. It is similar to the Mohs' hardness scale, which scratches the material. It is used to test the hardness of metals. Normally, a steel ball is pressed into an object and the dent made is measured.
CAS registry number
A CAS registry number is a unique number given to every chemical substance by the Chemical Abstracts Service (CAS). It is also called CASRN or CAS number. CAS registry number is also given to organic, inorganic compounds, minerals, isotopes, alloys. They are numbers ending with a check digit. They do not contain any structure information of the chemical.
It now identifies more than 164 million organic and inorganic substances. 68 million protein and DNA sequences are identified also. It is updated with around 15,000 new substances everyday.
Jeff Heerema
Jeff Heerema (; born January 17, 1980 in Thunder Bay, Ontario) is a Canadian professional ice hockey winger. He was drafted in the first round, 11th overall, by the Carolina Hurricanes in the 1998 NHL Entry Draft.
Danny Gruen