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

Many covalent compounds can be drawn by inspection using the valence electrons and the knowledge that covalent bonds are shared bonds. Just determine the Lewis dot structures of the atoms and the number of bonds for each atom. Then pair up the available electrons for the covalent bonds and draw the molecule.

Although, many molecules can be drawn by inspection others require the use of a few rules to help put them together. So, read the following rules carefully and think.

Complex Compounds

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

The least electronegative atom is the central atom, except hydrogen which is always a terminal atom.
Oxygen atoms do not bond with each other except in O2 and O3 molecules; peroxides; and super peroxides.
In oyxacids (ternary acids), hydrogen usually bonds to the oxygen instead of the central atom.
For those that have more than one central atom, the most symmetrical skeletons possible are used.
Step Two Calculate the number of electrons being shared (bonding electrons).

Determine the total number of electrons needed for each atom to complete its octet or duet (N).
Determine the total number of valence electrons already available (A). Remember to add electrons for negative charges and subtract electrons positive charges.
Subtract the electrons available from the electrons needed to get the number or electrons shared (S). S = N – A
Divide the shared (S) by two for the number of bonds in the molecule or polyatomic ion. S/2 = bond pairs
Step Three Place the bonding electrons in the skeleton as shared pairs.

Place one pair of electrons between each pair of bonded atoms.
If the central atom does not have a complete octet add double or triple bonds as needed.

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

Place lone pairs about each terminal atom to complete the octet rule.
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

The octet rule is just an observation of how main-group elements tend to combine in certain ways to fill their valence shell and become stable with 8 electrons, in order to gain the same electron configuration of the noble gases. A Lewis-Dot Structure can be used to show the bonding between atoms and how many electrons are in their valence layer. Some of the ways an atom can become fully stable with 8 valence electrons are through covalent bonding and ionic bonding. Covalent bonding is when two or more atoms share their electrons to fill their valence shell. We can use carbon dioxide as an example. There is one carbon atom with 4 valence electrons and 2 oxygen atoms with 6 each. In this case, the carbon atom can share 2 electrons to each oxygen atoms to fill their outer layers, and each oxygen can also share 2 of their electrons with carbon to give it the 4 electrons it needs to have 8. Now, both oxygen atoms and the carbon atoms are filled, stable, and have created water. Ionic bonding is when 2 or more atoms, usually metals with low electronegativity and non-metals with high electronegativity, trade their valence electrons in a way that they’ll all end up with 8. Electronegativity is the atoms’ attraction or ability to take in electrons. If an atom has over 4 valence electrons, they will take the amount needed to fill. If they have fewer than 4, they will lose the necessary to become stable. For example, sodium fluoride requires 1 sodium atom and 1 fluorine atom. Sodium has 1 valence electron and fluorine has 7. In this case, since sodium’s electronegativity is so low, it will lose its only valence electron to fluorine. When sodium loses that last electron, its previous layer becomes the new valence shell. When that lost electron goes to fluorine, it becomes stable with its full valence shell, just like sodium.

There are different ways to know how many valence electrons an element has. The easiest ways are looking at a Lewis Dot Diagram or simply at the periodic table. A Lewis Dot Diagram is the abbreviation of an element and a number of dots around it. Each dot around the abbreviation represents one valence electron. To figure it out looking at a periodic table all you have to do is find the element and look at what group it’s in. The columns in the periodic table are known as groups. They are numbered 1-18 but we’ll only be paying attention to numbers 1-2 and 13-18 because these are the main group elements. The group number symbolizes how many valence electrons it has, but for the double-digit groups 13-18, it only contains the amount shown in the second digit. For example, elements in group 14 have 4, elements in group 15 have 5, and so on. The downside to the periodic table is that the number of valence electrons in metals cannot be figured. A third way this could be figured out is through electron configurations. Electron configurations show the amount of electrons in each layer. The coefficients represent the layer, or energy levels, and the superscripts represent the amount of electrons. The electron configuration of sodium is 1s22s22p63s1. Its first energy level has a full layer, as well as the second. But the third only has 1 electron. This method works for any atom, including metals.