Contining on from CHM1045 over there are several topics that you must have a firm grasp on in order to have the ability to understand the ideas being presented in CHM1046.

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1) The structure of the atom

2) Valence electrons

3) Lewis Structures

4) Ions and salts

5) Polarity

Let"s begin with the very first of this topics: The structure of the atom.

An atom is made up of protons, neutrons and also electrons. Protons and also Neutrons are located in the cell nucleus of the atom and electrons are located in shells bordering the nucleus.


An elements atomic number is equal to the variety of protons located in its nucleus. If you change the variety of protons, you adjust the facet you room talking about. The atom mass the an facet is equal to the massive of its protons plus that is neutrons. From the mass in the regular table and the atom number, girlfriend should be able to determine the variety of neutrons in the atom.


Oxygen has an atomic number of 8 and a massive of ~16 amu. This suggests that there room 16 - 8 = 8 neutrons in the cell core of one oxygen atom.

The variety of electrons in an atom is constantly equal to the variety of protons so long as the atom is neutral. As soon as the number of protons (+ Charges) don"t equal the variety of electrons (- Charges) the atom is dubbed an ion. Negatively charged atoms are dubbed anions and positively charged atoms are called cations.

Ions type to increase the stability of the atom. Team VIII elements, the noble gases, space the many stable elements and also have eight valence electron (outermost covering electrons). Every one of the other aspects in groups I -VII type ions and also bonds in an initiative to obtain eight electron in your outermost shell.

Example: Nitrogen is a team V element. In bespeak to end up being like the noble gas Neon, the must gain 3 electrons. Therefore when Nitrogen develops ions, they have a 3- charge and also when it creates bonds it typically bonds to three various other elements.


The structure of Ammonia shown above is a Lewis Structure. Lewis frameworks are depictions of molecule that usage lines for bonds and show dots because that lone bag of electrons. There space some simple rules for drawing Lewis frameworks that you have to be familiar with:

Lewis structures are built in bespeak to meet the octet rule for every of the atom in a molecule. Binding are represented by “-” and also lone pairs of electrons are represented by “:”.

There are straightforward steps to developing a correct Lewis structure:

Step1: calculation the total variety of valence electrons available.

Let’s use PO43- as our example.

We require to recognize how numerous electrons are obtainable to do the bonds for Phosphate Ion.

Phosphorus is in team VA therefore it has actually 5 valence electrons and Oxygen is in group VIA so every oxygen has actually 6 valence electrons. Full valence electrons = 5 + 4(6) = 29. However wait a minute, that is an odd variety of electrons and also we haven"t really discussed that worry so something must be missing....Oh, the charge. For each an adverse charge on one ion, we need to include 1 valence electron therefore this provides the complete 29 + 3 = 32 valence electrons.

This method we have actually 32 electron to distribute right into bonds to create phosphate ion.

Step 2: recognize which atom will be central in the molecule.

The main atom in a molecule is typically the the very least electronegative atom. That is additionally often the atom i m sorry will enable you to develop the many symmetrical molecule. Because that phosphate, PO43-, the phosphate is the the very least electronegative atom and also it will allow us to make the many symmetrical molecule so the is the many likely central atom. ~ above a side note, for other molecules the contain hydrogens, we know that hydrogen can only do 1 bond therefore hydrogen atoms can NEVER it is in the main atom.

Step 3: Arrange atom symmetrically about the main atom.

Most the nature’s inventions are symmetrical and also the very same holds true for most moment-g.comical compounds. When writing Lewis structures, the many symmetrical arrangement of atoms around the main atom is best.

For phosphate:

The four oxygen atoms are placed symmetrically roughly the phosphorus.

Step 4: location bonds/electrons roughly the atoms until the octet rule is satisfied because that each atom. Use double or triple bonds if necessary. You have to use up every one of the valence electrons. (Note the charge displayed are officially charges ~ above those ions)


Step 5: Show any charges on the molecule using brackets < > and place the fee in the upper appropriate hand corner just external the brackets


The Phosphate ion shown over can be an unified with positive ions to type salts. A salt is one ionic link (metal + non-metal) that is formed when two oppositely charged ion come together to kind a neutral compound.

Example: sodium Phosphate = Na3PO4 This is a salt written of the Na+ and also PO43- ions. In ~ this suggest you should have the ability to construct the exactly salt indigenous any combination of confident and an adverse ions and also name the result compound. If you still can"t perform this an extremely well you should practice!!

Ionic compunds are considered the many polar kind of molecule since they every dissociate in water to some extent. Various other molecules, covalent molecules, execute not dissociate right into parts in water and also are because of this considered non-polar.

A 3rd group the molecules are both covalent and polar and also therefore carry out mix come some level with water. A great deal of the material in the first few chapters the CHM1046 will rely on your expertise of these varieties of compounds so girlfriend will require to be able to discern whether a molecule is polar or not.

What causes polarity?

Polar molecules contain an electronegative atom that pulls the electron in the molecule in the direction of itself and also away indigenous the other atoms in the molecule. You can think the it together a popular contest and also the most electronegative atom is the many popular. The electrons all desire to spend more time about it. Once this wake up the circulation of electron (- Charges) are focused at one suggest in the molecule and also the protons (+ Charges) the the other atoms space left rather exposed. This uneven circulation produces what is called a dipole and molecules that contain dipoles are considered to be polar.

In this case, the Cl atoms are much more electronegative 보다 the carbon forming partial dues on the atoms and a dipole.

So which elements are electronegative? The many electronegative aspect is Fluorine and the tendency of electronegativity increases from left come right and also from bottom to peak in the periodic table.

Other an easy trends the you have to be conscious of space trends in ionization energy and atomic radius.

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The ionization energy or ionization potential is the energy necessary to eliminate an electron from the neutral atom. It usually increases indigenous bottom to peak (it is much easier to take it an electron away from one atom with many electrons than from one with simply a few electrons) and also from left to appropriate in the routine table. As you move from left to right throughout a period of the routine table, you boost the variety of protons in the nucleus however you continue to be within the very same orbital shell. This means that the pull towards the nucleus is raising as you go from left to right however the shielding (electrons in the inner shells) is staying constant. If the electrons are being organized onto tighter then the energy to rest them cost-free is going to increase. The is why facets on the far right of the table (except for the noble gases) all accept electrons far much better than they give them up.

The atom radius boosts from height to bottom and also from right to left in the routine table. From peak to bottom renders sense because you space adding huge numbers the electrons, but the increase in size from appropriate to left is frequently confusing. Together you move from left come right across a period of the regular table, you boost the number of protons in the nucleus however you remain within the same orbital shell. This method that the pull towards the nucleus is boosting as you walk from left to right yet the shielding (electrons in the inner shells) is staying constant. This means that the electron in the outer shell room being pulled in tighter and also tighter together you go across the duration and hence the atom radius is shrinking.