Cations Vs Anions

In chemistry, an atom is the smallest unit of matter containing particles. When a group of atoms join together and the number of electrons is equal to the number of protons it is called an ion. Depending on the ratio between electrons and protons, two different types of ions can be formed. They can form cations or anions. A cation is formed when the ratio between electrons and protons has more protons than electrons, therefore making it positively charged. An anion is formed when the ratio between electrons and protons has more electrons than protons, therefore making it negatively charged. Atoms join together in groups because of electronegativity. Elements on the left side of the periodic table use more energy to bond therefore losing more electrons and creating cations. However, elements on the right side are more energy efficient therefore attracting more electrons and creating anions. Electronegativity increases moving right across the periodic table. As you move down a group, electronegativity decreases. This is because the atomic number increases down a group and thus there is an increased distance between the valence electrons and the positively charged nucleus. This form of organization is credited to Dimitri Mendeleev as he was the founder of the periodic table.

When an atom loses electrons that is called oxidation. When the atom is oxidized it is called the reducing agent. When an anion is oxidized it loses electrons and therefore has the potential to become an cation.
Some examples of an anion would be Cl2, Br2, and I2. An example for cations would be (SO4)2-, (CO3)2-, and (C2O4)2-. The similarities between the cations is that all Alkaline Earth Metals are in Group 2A, which forms cations, while all halogens are elements in group 7A form anions. Cations are usually formed between metals while anions are usually formed between nonmetals.

According to the experiment in the Laboratory of Chemistry, if you can classify Alkaline Earth Metals, you can tell if the ion is an cation or an anion. This experiment consists of aqueous nitrate solutions being mixed with an polyatomic anion. Oxidation is important in terms of cations and anions, because if an anion is oxidized it has the potential to be a cation. In the second experiment it was revealed that the halogen with the more positive electrode would be the stronger reducing agent.

Chemistry – How to Draw and Use Lewis Electron Dot Symbols in Chemistry

Lewis dot symbols are useful in showing the arrangement of the valence electrons in an atom. The valence electrons are the electrons in the outermost energy level of an atom and are instrumental in forming chemical bonds.

So, Lewis dot symbols can be used to determine the charge of the ion formed, the oxidation number and the number of bonds for the element. But an even better use for electron dot symbols is to join them together to form the Lewis structures of molecules or polyatomic ions.

The purpose of Lewis structures is to show the number and kinds of bonds, and the way in which the atoms or ions are connected in the molecule or polyatomic ion. Many of these structures are simple and can be determined by inspection. While, others are a bit more complicated and require some thinking.

Simple Molecules



Complex Compounds

Step One Determine the “skeleton” for the molecule or polyatomic ion.



Place one pair of electrons between each pair of bonded atoms.

Step Four Place the leftover electrons (A – S) in the skeleton as lone pairs.

Leftover electron pairs are placed on the central atom.
If the central atom is from the third or higher period, it can accommodate more than four electron pairs (expanded valence).

Electron Emission From Metal

A metal can be considered as the collection of a conglomeration of crystal with various shapes and sizes. Each crystal consists of a nucleus and orbits surrounding nucleus. The nucleus can be considered as the positive charged portion and in the orbits, electrons are revolving. Since electrons have negative charge, we can consider orbits with negatively charged electrons revolving with a velocity of light. The valence electrons, ie, the electrons in the outermost orbits decide the chemical behavior of an atom. When we brought similar atoms close to each other, the electrons in the metal try to move from one atom to another. In a random way, the valence electrons with high potential energy will move very freely from atom to atom. These electrons which can move freely in an atom are called as “free electrons”. When the valence electrons reach the surface of metal, it encounters a potential energy barrier; the kinetic energy of such electrons will get reduced to zero and is turned back into the body of the metal.

If the energy is greater than zero, it emits from the metal surface. The “work function” of the metal can be defined as this minimum amount of energy required at absolute temperature to make some electrons to escape from the metal.

The electron emission can be classified as,

1. Thermionic Emission
2. Secondary Emission
3. Photoelectric Emission
4. High Field Emission

Thermionic Emission:

From the name itself, the thermionic emission deals with the effect of heating. We know that when a metal is heated, its temperature increases and the kinetic energy of some of the electrons in the metal may increase beyond the fermilevel so as to surmount the potential energy barrier of the surface. These electrons can escape from the metal and yields to a type of emission called ‘Thermionic Emission’. Thermionic emitters are of two types,

1. Directly heated Emitter
2. Indirectly Heated Emitter (Oxide Coated Emitter)

Directly heated Emitters are,

1. Tungsten Emitter
2. Thoriated Tungsten Emitter

Secondary Emission:

When a moving particle strikes a solid with higher velocity, major portion of its kinetic energy will get transferred to one of the electrons and enables the escape of electrons through the potential barrier at the surface of the solid yields to a process of electron emission called as secondary emission. The electrons thus liberated are called as the secondary electrons, the high velocity particles strikes the solid to cause the secondary emission and are called as primary particles. Such electron emission is desirable in devices like electron multiplier tubes, dynatrons, television camera tubes etc. and which is undesirable in most of other devices. The secondary emission ratio can be defined as the number of secondary electrons emitted per primary particle. When the kinetic energy of a primary particle is large, it will energize and leads to liberate more than one electron on the target surface.

The secondary emission ratio depends on,

1. Target Material and Surface Condition.
2. Energy of primary particle.
3. Type of primary particle.
4. Angle of incidence of the target surface.

The Octet Rule

