P block elements are those of groups 13-18 of the periodic table. Block includes a mixture of p block metals and non-metals. Semi-metal germanium, arsenic, antimony are found in this block. All these elements have p-type orbital partially occupied. These elements show a greater variation of physical and chemical properties compared with those of type s block. P block includes highly reactive halogens and a number of very important non-metals such as carbon, nitrogen and oxygen. These elements tend to form covalent compounds between them. Also in block p is found and noble gases. Halogens form covalent compounds with non-metals. Not only the chemical, but most of the physical properties of halogens vary regularly with increasing number of the elements.
Halogens are found in the earth' crust in the form of compounds.
The most important ore of fluorine is fluorine CaF2. Fluoride enters in the human organism composition: the enamel of teeth, bones, nails and hair.
The most important minerals of chlorine are rock salt Na Cl, sylvite KCl. NaCl. NaCl are both in the earth's crust, as in the state dissolved in sea water (-3%), salt lakes.
Bromine is found in nature as compounds - bromides (sodium, potassium and magnesium) in sea water, but in smaller quantities than chlorine. Bromides are accompanying chlorides in deposits.Deposits of carnallite always contain bromides KBR. Halogens are necessary for vital activity of organisms. Human body contains 0.25% chlorine. Iodine enters in the thyroid hormone composition. Chemical properties of halogens.
Fluoride is the most active non-metallic. Combine it with hydrogen in the dark and at - 252 ° C with explosion. Combine strongly with many metals except platinum and gold. Some metals, such as copper, nickel, magnesium, fluorine are stable over because the surface of the metal film is formed by fluoride, which protects the interaction of metals on. Non-metals, apart from nitrogen and oxygen, combine directly with fluorine, iodine, sulfur and silicon and carbon is ignited in a stream of fluorine. Fluoride decompose oxides and combine with metal oxides or non-metallic oxide. He also breaks down water with formation of hydrogen fluoride, fluoride of oxygen, hydrogen peroxide and ozone:
F2 + H2O = 2HF + O
H2O + 0 = H2O2,
A + F2 = OF2,
3O = O3.
A covalent compound is a compound in which the atoms that are bonded share electrons rather than transfer electrons from one to the other.
The reason that nonmetals have to share electrons with each other has to do with electronegativity. Recall that electronegativity is a measure of how much an element pulls electrons away from other elements it is bonded to. Metals generally have very low electronegativities (they don't much want to grab electrons) while nonmetals have high electronegativities (they really want to grab electrons). The reason for this trend is the octet rule, which says that all elements want to have the same number of electrons as the nearest noble gas, because noble gases are unusually stable. When metals bond to nonmetals, ionic compounds are formed because the metal atoms don't want electrons and easily give them to nonmetals that do want electrons.
The compounds whose molecules consist of atoms held together by covalent
bonds are known as covalent compounds. Their general properties are:
1) State of existence
2) Low boiling and melting point
4) Non- conducting
5) Molecular reactions
6) Directional character of the bond
Covalent compounds are compounds have molecules that are formed by sharing common pairs of electron between its atoms. In contrast molecules of ionic compounds which are formed by transfer of electrons from one atom to another. There are no hard and fast rules regarding properties of covalent compounds, but there is a general pattern. Covalent compounds display following general characteristics.
- Covalent compounds tend to have lower melting and boiling points compared to ionic compounds.
- Covalent compounds tend to be softer compared to ionic compounds.
- Covalent compounds tend to be more inflammable compared to ionic compounds.
- Covalent compounds don't conduct electricity in water
- Covalent compounds are usually not soluble in water.