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| Types of chemical compounds | - |
Types of chemical compounds
Chemistry is the science of the compounds of Atoms.
What are the types of compounds the atoms bond with?
The 3 most significant bonds are:
- Ionic bond
- covalent bond
- metallic bond
on the other hand in the inorganic chemistry there is a specialty
- complex compounds
except of these types there are bonds like
- hydrogen bonds and
- van der Waals interactions
The ionic bond
Further above we have mentioned the ions which are known as cations and anions .
An ionic bond is composed of a cation and an anion . Simple example,
NaCl , sodium chloride . Cation is the sodium cation, Na+, and the anion is the chloride anion Cl-.
Elemental sodium emits an electron and becomes a cation. The chlorine atom absorbs this electron and becomes an anion .
Metal atoms form cations and non-metals become anions.
Polyatomic molecules or compounds are capable of forming both ions, cations and anions. For example ammonium nitrate, NH4NO3, NH4+ is the cation and NO3- is the anion.
Alkali metals can emit 1 electron, alkaline earth metals 2 and aluminum , Al , 3 electrons. Transition metals are able to give away more electrons .
Transition metals can emit up to 8 electrons Ru and Os.
Cr, Fe, Mo, W, Ir and Po can spend up to 6 electrtons Mn, Tc, Re 7 electrons.
KMnO4, Potassiumpermanganate, the cations, Potassium, K emits 1 and Mn the highest possible number of 7 electrons.
Potassiumpermanganate, (K+, Mn7+, and 4 O2-) is an important compound used in organic chemistry as an oxidant and as well in inorganic chemistry for quantitative analysis.
Ionization
The energy an atom has to spend to give away an electron is calledIonization. That one of the sodium it is 496kJ / mol.
Na ===> Na+ + e-
(For a single electron ionization energy is also given in electron volts. 1 eV = 1.6022 * 10exp-19 J. This value corresponds, the kinetic energy of an electron that has been accelerated by a potential of 1 volt in vacuo. For 1 mole of electrons, this gives: 6.022*10exp23*1.6022* 10exp-19 = 96’484J or about 96.5kJ/mol.)
In the periodic table (see last chapter) the ionization energy arises within a period from the left to the right and within a major group.
Electron affinity
The energy, which is needed to absorbe an electron is called electron affinity.
Cl + e- ===> Cl-.
If a chlorine atom gets an electron, energy is released. -328kj/mol.
An electron approaches an atom it is attracted to the nucleus and repelled by the electron. Thereby energy is released or has to be spended.
When helium absorbs an electron, 21kJ/mol is required.
Other example of ionic bonds, nomenclature
CaCl2, Calciumchloride for working waterfree in laboratories
NaF, Sodiumfluoride, main compound of toothpastes
NH4Cl, Ammoniumchloride. When fumes of ammonia, NH3 and hydrochloric acid, HCl get together, you see a white cloud.
Nomenclature of some essential anions with two or more Elements:
OCl- = hypochlorite
ClO3- = chlorate
ClO4- = perchlorate
SO3(2-) = sulfite
SO4(2-) = sulfate
NO2- = nitrite
NO3- = nitrate
CO3(2-) = carbonate
C2O4(2-) = oxalate
The covalent bond
Thsi subchapter is very important for those who want to study the organic chemistry.
An electron in an atom describes a wave equation. 2 atoms with the same waves to overlap. The amplitudes of the two waves add up. The increased negative charge density of the electrons, it comes to attracting the positively charged atomic nucleus. In higher lessons you will learn more about the quantum physical properties.
Here we are dealing with valence bond, (Lewis creator) octet rule, electronegativity and dipole.
As mentioned above noble gases, see 8th main group of periodic system do not react with any chemical elements, they are inert and in chemistry of little importance.
H, O, N, F, Cl, and other elements do not exist as individual Atoms like the noble gases do. Now Gilbert N Lewis has developed a concept that the goal of each atom is to achieve the noble gas configuration.
Hydrogen, H2, reaches the 2-electron configuration of helium. He and hydrogen gas H2 are isoelectric, consist of two electrons.
Other noble gases Ne, argon Ar, krypton, Kr, Xenon, Xe and radon, Rn, with 8 electrons. All these noble gases have eight electrons in the outermost sphere, which is complete. So they cannot enter into any bonds.
This is the octet rule of Gilbert N Lewis.
It follows the octet rule: an absence of one or more electrons in the outermost sphere.
The octet rule is valid for nonmetals especially for maingroups 4-7 of the 2nd period.
The electrons of the outmost sphere are called valence-electrons.
The number of valence-electrons of C, N, O, F ( incl.other halogenids Cl,Br,I) are 4, 5, 6, and 7 and match with the number of the main group.
Remember noble gases have 8 valence-electrons.
So, howmany bonds can we get? the octet ruel is 8 – N.
Facit: Carbon, C, hase 4 valence electrons. 8 – 4 = 4 bonds
Nitrongen N,with 5 valence-electrons, 8 – 5 = 3 bonds.
O = 2 bonds and the halegonids F,Cl,Br,I 1 bond.
Coming back to the structural formulas above.
Every atome has to be surrounded by 8 electrons, this is the main point of the octet rule. So when signing a structural formula never forget the nonbond electronpairs of each element! (go back to chapter above, structural formulas)
To explain the compound, carbon dioxide, in the picture above: the double stripes are bonding electronpairs containing totally 4 electrons each double stripe.
the two stripes on the right and left outside of the element oxigen, O, are nonbonding electronpairs.
Electronegativity and Dipole
Electronegativity is a measure of how readily an atom is willing to loose or accept an electron. Big electronegativities are found in non-metals , fluorine, F , is the most electronegative atom with 4.0. Small electronegativities are found with alkali and alkaline earth. K , Rb, Cs have the smallest electronegativity 0.8.
The calculations of the electronegativities are based on the binding energies . The values of electronegativities are not exactly and have no unity. There are relative values.
Generally, based on the periodic table, the electronegativities increase from left to right and decrease from top to downwards.
Attention: the electronegativity of each noble gase is zero!
Compounds, whose atoms have different values of their electronegativities or have a lack of symmetry, are likely to have a dipole.
H – Br, H – I, for example, each have a dipole . Br and I are more electronegative than H. (see table above)
H2 , Cl2 and O2 have no dipole, the difference in relative electronegativity is zero.
dipole moments of more complicate compounds can be determined or calculated geometrically and mathematically. More about that in mathematics and physics and higher lessons.
H2O and NH3 have a dipole . H2O is angled ( 109 ° )
CO2 has no dipole, < O == C == O > is straight.
The unity of the dipole or dipole moment is Cm, (Coulomb * meter) . A physical unit. In earlier times the unit of dipole moment was called Debye.
The metallic bond
More than three quarters of all the elements are metals
The most important properties of metals are : high thermal conductivity, metallic luster, malleability and large electrical conductivity .
Generally: Nucleuses are Swimming in a lake of electrons. Nucleuses are shaking. This is the main reason why electricity is expensive. It means electrons are obstructed in moving by shaking nucleuses.
Because metals have low electronegativities they give easily away electrons and become cations.
More about the chemistry and physical properties of metals, you’ll experience later here.
The bond of complex compounds
A complex compound consist of a central atom, these is usually a transition metal. Around this central atom ions or molecules arranged geometrically and they are called ligands. The ligand must have a free electron pair, which it can spend to the central atom. (When a molecule’s free electron pair is given away to its reactants, it’s called a Lewis base, more about that later)
The nature of the bond between ligand and central atom can be both covalently and ionic.
The number of ligands bound to the central atom is called coordination number and the space body which arises here is a coordination polyhedra.
In most of the complexes we find coordination numbers two, four and six. The coordination polyhedra occur linearly, tetrahedral, square planar and octahedral.
The charge of a complex consists of the charge of the central atom and its ligands. The formulas are provided with brackets.
Example Al 3+ has 4 ligands as chloride ions Cl-, which gives [AlCl4] -. This compound has a tetrahedral structure.
Complex with 4 ligands can exist either in tetrahedral and in square planar structures. Complexes with six ligands have an octahedral structure. See Picture
These 3 complexcompounds are ions! To equalize the charge theyneed a corresponding anion or cation. [Co(NH3)6]Cl3 for example, its name is Hexammincobalt(III)trichloride
Complex compounds are practically used in analytical chemistry, biochemistry , water treatment, electrochemistry and bacteriology. Natural complex compounds are present also in the organism and in the biological nature. Chlorophill is a complex with the central atom of magnesium . It is responsible for green color of vegetation. Hemoglobin in the blood with iron as the central atom is also a complex . Among the vitamins, B12, cobalamin is known, its central atom is cobalt, Co.
Hydrogen bonds and Van der Waals interactions
Hydrogen bonds
Hydrogen atoms are attracted by non-binding or lone electron pairs of atoms which are very electronegative. these compounds can be designated in dotted lines: H … / O – H – O \ … H. water, H2O, there are the lone electron pairs of the oxygen atom, which enable hydrogen bonds with the hydrogen atom. Other examples of ammonia, NH3, H … / … NH2H / N. and hydrohalic acids such as HF, HCl, HBr and HI.
Water would be gaseous even at 0 ° C with absence of these hydrogen bonds and life would be non-existent. Likewise, the nucleus, the DNA (deoxyribonucleic acid) does only exist thanks to hydrogen bonds.
Van der Waals and London interactions
Here are weak intermolecular interactions between molecules with dipole. London interactions come about when the electron cloud of a molecule is temporarily deformed, thereby an instantaneous dipole moment exists.