PERIODIC CHEMISTRY

The periodic table is a table showing the elements prearranged in order of increasing atomic number, in accordance with the periodic law. In the periodic table, elements that have related chemical properties and electronic structures are placed in vertical columns known as the groups.

Periodicity of the elements

Periodicity is one among the basic aspects of the elements in the periodic table.

What Is Periodicity?

Periodicity of elements means the persistent trends that are visible in the properties of element. These trends that exist in the property of elements became noticeable to Mendeleev when he prearranged the elements in the periodic table order of increasing mass. From the properties that were displayed by the recognized elements, it was easy for Mendeleev to foretell where there were “breaks” in his table, or elements that were not yet discovered.

The contemporary periodic table is extremely related to Mendeleev's table, but in the present day elements are prearranged in the order of increasing atomic number, which showcases the number of protons in an atom. There are no unidentified elements; even though fresh elements can be formed which have even larger numbers of protons.

The Periodic Properties are enumerated below:

1. Ionization energy – Ionization energy is energy needed to remove an electron from an ion or gaseous atom.

2. Atomic radius – Atomic radius is the distance between the centers of two atoms that are in close relationship with each other.

3. Electronegativity – This is a measure of the ability of an atom to form a chemical bond

4. Electron affinity –This is an ability of an atom to accept an electron

Periodic Trends or Periodicity

The periodicity of the above properties follows trends as you go across a row or period on the periodic table or down a column or group on the periodic table.

While moving from Left to Right-across the period

• Ionization Energy Increases

• Electronegativity Increases

• Atomic Radius Decreases

While moving Top to Bottom-down the group

• Ionization Energy Decreases

• Electronegativity Decreases

• Atomic Radius Increases

The definition of the Periodic Law

The Periodic Law states that the physical and chemical properties of elements in the periodic table reappear in a methodical and conventional way when the elements are prearranged in order of increasing atomic number.


The elements of the first transition series

Even though the transition elements have a lot of broad chemical similarities, every one of them has a thorough chemistry of its own. The adjoining relationships are typically found amongst the three elements in every vertical group of the periodic table, even though inside every group, the element of the first series typically varies more from the rest two than they vary from each other. The majority of the first series elements are more recognizable and theoretically significant than the heavier members of their vertical group.

A small number of the chemical trends among the elements of the first transition series may be capsulated.

1. Titanium to manganese exhibits the highest oxidation state, which is normally found among oxo compounds, fluorides, or chlorides and corresponds to the total number of 3d and 4s electrons in the atom. The stability of this uppermost oxidation state decreases from titanium in the +4 state to manganese in the +7 state. Next to manganese—ie among iron, cobalt, and nickel, oxidation states related to the loss of all 3d and 4s electrons do not take place; higher oxidation states generally turn out to be increasingly more complicated to reach because the growing nuclear charge makes the 3d electrons to be additionally securely bound. It is only the following elements that exhibits very high oxidation states - chromium (+5, +6 states), manganese (+5, +6, +7 states), and iron (+5, +6 states) and with the exception of fluorides, such as chromium pentafluoride, CrF5 (where the chromium is in the +5 state), and chromium hexafluoride, CrF6 (where chromium is in the +6 state), and oxofluorides like manganese trioxide fluoride, MnO3F (occur with manganese in the +7 state), the most important chemistry in these variable oxidation states is that of oxo anions such as permanganate, MnO4− (+7 state); chromate, CrO42− (+6 state); and ferrate, FeO42−(+6 state). Every one of these compounds is very good oxidizing agent.

2. The oxides of the entire element become more acidic as the oxidation number increases, and the halides become more covalent and able to easily undergo hydrolysis.

3
. In the oxo anions that are mostly found in the higher oxidation states, the metal atom is tetrahedrally bordered by oxygen atoms, while in the oxides created in the lower oxidation states, the atoms are typically octahedrally synchronized.

4. In the oxidation states of +2 and +3, complexes in aqueous solution or in crystals is typically four, five or six step.

5. Oxidation states less than +2 are not regularly found in the chemistries of the transition elements, apart for copper although it could be found in all the elements through the use of ligands like that of carbon monoxide.

The group 7 elements (The halogens)

Elements of group 7 are as well known as the halogens. They consist of fluorine, chlorine, bromine and iodine. All of them have seven valence electrons in their outside shell.

In a displacement reaction, a less reactive element is displaced by a more reactive element.

The group 7 elements are put in the vertical column second from right in the periodic table.

Chlorine, bromine and iodine are the three Group 7 elements that are mostly available in the secondary school. Fluorine is excessively reactive and cannot easily be produced and preserved in the school. Reaction of Group 1 elements reacts with group 7 element to form salt and because these, they are known as ('salt formers').

Properties and uses of the halogens

The table summarizes some of the properties and uses of three halogens.

Group 7 element Properties Typical use

Chlorine Green gas Sterilising water

Bromine Orange liquid Making pesticides and plastics

Iodine Grey solid Sterilising wounds

Iodine forms a purple vapour when it is warmed.

Group 7 properties

The halogens are diatomic which means that they exist as molecules, each with one pair of atoms. The formulas for their molecules are written as Cl2, bromine Br2 and iodine I2.

Physical properties of halogens

The halogens show trends in their physical properties down the group.

Melting point and boiling point

The halogens or elements of group 7 have low melting points and boiling points. This is a characteristic property of non-metals. Fluorine has the smallest melting point and boiling point. The melting points and boiling points of halogens starting form flouring increases down the group.

Melting and boiling points of Group 7 elements

State of the halogens at room temperature

25°C is normally considered as the room temperature. At this particular temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids. There is for that reason a trend in state from gas to liquid to solid as you move down the group.

The Colour of the halogen

The halogens happen to be darker as you move down the group. Fluorine is extremely pale yellow, chlorine is yellow-green, and bromine is red-brown. Iodine crystals are glossy purple - but they when they are heated up, they easily change into a dark purple vapour.

Predictions

When we can see a trend in the properties of some of the elements in a group, you can likely calculate the properties of other elements in that group. Astatine is placed after iodine in Group 7. The colour of halogens turns darker as you move down the group. Iodine is purple colour, and, as we would imagine, astatine is black-coloured.

The Halogens are commonly non–metals. 'Halogens' means 'salt formers' and the most widespread compound is sodium chloride which can be found naturally in the form of deposits of 'rock salt' or the much more abundantly as the 'sea salt' in the seas and oceans.

The reason Why the melting points and boiling points of Group 7 elements increase with atomic number or down the group

This increase in melting/boiling points down Group 7 is as a result of the increasing weak electrical intermolecular attractive forces that occur with an increase in the size of atom or molecule.

In general, the greater the number of electrons in a molecule, the greater the force of attraction that exist between the molecules.

A table showing the properties of group 7

Symbol and Name Atomic Number Electron arrangement State and colour at room temperature and pressure Melting point Boiling point atom radius pm
F Fluorine 9 2.7 pale yellow gas –219oC, 54K –188oC, 85K 64
Cl Chlorine 17 2.8.7 pale green gas –101oC, 172K –34oC, 239K 99
Br Bromine 35 2.8.18.7 dark red liquid –7oC, 266K 59oC, 332K 114
I Iodine 53 2.8.18.18.7 dark (black) crumbly solid 114oC, 387K 184oC, 457K 133
• The halogens are all poor conductors of heat and electricity – characteristics of non–metals.

• When they are in the solid state, they are brittle and crumbly example. iodine.

• The density increases down Group 7.

• The size of the atom gets bigger down Group 7 as more inner electron shells are filled going down from one period to another.

Chemical features, similarities, and physical property and reactivity trends

1. The atoms all have 7 outer electrons, this outer electron similarity, just like any other Group in the Periodic Table, gives them a very similar chemical properties.

2. They form a single charged negative ions e.g. chloride Cl– because they are one electron less than that of a noble gas electron structure. They only need to gain one negative electron (reduction) to be stable and this gives them a surplus electric charge of –1. These ions formed by the halogens are known as the halide ions, two other halide ions are called the bromide Br–and iodide I– ions.

3. They form ionic compounds with metals e.g. sodium chloride Na+Cl–.

4. The Halogens form covalent compounds with non–metals and with themselves.

5. The bonding in the molecule of halogen compound involves single covalent bonds like the hydrogen chloride HCl or H–Cl.

Important things to note when naming halogen compounds:

When joined with other elements to form simple compounds, the name of the halogen element alters a little from ...ine to ...ide.

Fluorine forms a fluoride (ion F–), chlorine forms a chloride (ion Cl–), bromine a bromide (ion Br–) and iodine an iodide (ion I–).

The other element at the beginning of the compound name like the hydrogen, sodium, potassium, magnesium, calcium, and so on remains unaltered.

So archetypal halogen compounds are named as follows:

• Potassium fluoride, hydrogen chloride, sodium chloride, calcium bromide, magnesium iodide and so on.

The elements of group 7 all exist as diatomic molecules ie X2 or X–X, where X stands for the halogen atom.

A halogen that is more reactive displaces a less reactive one from its salts.

(pics and table refusing to upload)

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