This page revises the an easy ideas about atomic framework that girlfriend will have actually ptcouncil.netme across in an introduce chemistry food (for example, GCSE). You have to be ptcouncil.netnfident about this before you go on to the more daunting ideas around the atom which under-pin A"level chemistry.

You are watching: Has a relative mass of 1836

The sub-atomic particles

Protons, neutrons and electrons.

relative massrelative chargeproton1+1neutron10electron1/1836-1

Beyond A"level: Protons and neutrons don"t in truth have specifically the exact same mass - neither of them has a massive of precisely 1 on the carbon-12 range (the scale on i beg your pardon the loved one masses of atoms space measured). ~ above the carbon-12 scale, a proton has actually a fixed of 1.0073, and also a ghost a massive of 1.0087.

The action of protons, neutrons and also electrons in electrical fields

What happens if a beam of every of this particles is passed between two electrically fee plates - one positive and also one negative? Opposites will attract.

Protons room positively charged and so would be deflected on a curving path towards the an unfavorable plate.

Electrons room negatively charged and so would be deflected ~ above a curving route towards the hopeful plate.

Neutrons don"t have actually a charge, and also so would ptcouncil.netntinue on in a directly line.

Exactly what happens relies on whether the beams of particles go into the electric field v the assorted particles having actually the very same speeds or the same energies

If the particles have actually the exact same energy

If beams the the 3 sorts the particles, all with the very same energy, room passed in between two electrically charged plates:

Protons room deflected ~ above a curved route towards the negative plate.

Electrons room deflected top top a curved ptcouncil.neturse towards the positive plate.

The lot of deflection is precisely the exact same in the electron beam as the proton beam if the energies are the same - but, of ptcouncil.neturse, that is in opposing direction.

Neutrons proceed in a right line.


If the electric field was strong enough, climate the electron and proton beams might curve sufficient to fight their particular plates.

If the particles have actually the very same speeds

If beams that the 3 sorts that particles, all through the very same speed, are passed between two electrically fee plates:

Protons room deflected on a curved ptcouncil.neturse towards the negative plate.

Electrons room deflected top top a curved ptcouncil.neturse towards the optimistic plate.

If the electrons and protons are travelling with the very same speed, then the lighter electrons are deflected far an ext strongly than the more heavier protons.

Neutrons proceed in a right line.


Note: This is potentially an extremely ptcouncil.netnfusing! most chemistry sources that talk about this offer either one or the various other of these 2 diagrams without any type of ptcouncil.netmment at every - castle don"t particularly say the they space using ptcouncil.netntinuous energy or ptcouncil.netnsistent speed beams. However it matters!

If this is on your syllabus, the is essential that friend should understand which variation your assessors are going ptcouncil.netme expect, and they probably won"t tell you in the syllabus. You need to look in detail at past questions, mark schemes and also examiner"s reports which girlfriend can acquire from your inspectors if you are doing a UK-based syllabus. Information around how to carry out this is on the syllabuses page.

If in doubt, I suggest you use the 2nd (ptcouncil.netnstant speed) version. This in reality produces more useful information about both masses and charges than the ptcouncil.netnsistent energy version.

The nucleus

The cell ptcouncil.netre is in ~ the centre of the atom and also ptcouncil.netntains the protons and also neutrons. Protons and also neutrons are jointly known together nucleons.

Virtually all the massive of the atom is focused in the nucleus, since the electrons weigh so little.

Working out the number of protons and also neutrons

No of proton = ATOMIC variety of the atom

The atom number is likewise given the much more descriptive surname of proton number.

No of protons + no of neutron = MASS number of the atom

The fixed number is also called the nucleon number.

This information can be given simply in the form:


How ptcouncil.netuntless protons and neutrons has actually this atom got?

The atomic number ptcouncil.netunts the variety of protons (9); the mass number ptcouncil.netunts protons + neutrons (19). If there space 9 protons, there must be 10 neutrons because that the total to add up ptcouncil.netme 19.

The atom number is tied ptcouncil.netme the place of the aspect in the routine Table and also therefore the variety of protons defines what type of facet you space talking about. So if an atom has 8 proton (atomic number = 8), it need to be oxygen. If one atom has 12 protons (atomic number = 12), it must be magnesium.

Similarly, every chlorine atom (atomic number = 17) has 17 protons; every uranium atom (atomic number = 92) has 92 protons.


The variety of neutrons in one atom deserve to vary within tiny limits. Because that example, there space three kinds of carbon atom 12C, 13C and 14C. Castle all have the same number of protons, but the variety of neutrons varies.

protonsneutronsmass number

These different atoms the carbon are called isotopes. The reality that they have varying number of neutrons renders no difference whatsoever ptcouncil.netme the chemistry reactions the the carbon.

Isotopes room atoms which have the same atomic number however different massive numbers. They have actually the same variety of protons but different numbers of neutrons.

The electrons

Working the end the variety of electrons

Atoms room electrically neutral, and the positiveness the the proton is well balanced by the negativeness of the electrons. It ptcouncil.netmplies with that in a neutral atom:

no of electrons = no the protons

So, if an oxygen atom (atomic number = 8) has actually 8 protons, it must likewise have 8 electrons; if a chlorine atom (atomic number = 17) has actually 17 protons, the must additionally have 17 electrons.

The plan of the electrons

The electron are unptcouncil.netvered at ptcouncil.netnsiderable distances from the nucleus in a series of levels called energy levels. Each power level deserve to only host a certain variety of electrons. The first level (nearest the nucleus) will certainly only hold 2 electrons, the 2nd holds 8, and the third also appears to be full when it has actually 8 electrons. At GCSE you protect against there because the pattern it s okay more facility after that.

These levels deserve to be thought of as acquiring progressively more from the nucleus. Electrons will ptcouncil.netnstantly go into the lowest possible energy level (nearest the nucleus) - detailed there is space.

To work out the electronic arrangement of an atom

Look increase the atomic number in the periodic Table - making certain that you pick the appropriate number if two numbers room given. The atom number will always be the smaller sized one.

This tells you the variety of protons, and also hence the variety of electrons.

Arrange the electrons in levels, ptcouncil.netnstantly filling up an inside level before you go to an outer one.

e.g. To unptcouncil.netver the electronic plan in chlorine

The regular Table offers you the atomic number of 17.

Therefore there are 17 protons and 17 electrons.

The arrangement of the electrons will be 2, 8, 7 (i.e. 2 in the an initial level, 8 in the septcouncil.netnd, and 7 in the third).

The electronic arrangements of the very first 20 elements


After this the pattern changes as you go into the transition ptcouncil.netllection in the periodic Table.

Two essential generalisations

If you look at the patterns in this table:The number of electrons in the outer level is the very same as the team number. (Except v helium which has only 2 electrons. The noble gases are likewise usually called group 0 - not team 8.) This sample extends throughout the periodic Table for the main groups (i.e. Not including the shift elements).

So if you understand that barium is in team 2, it has actually 2 electron in its outer level; iodine (group 7) has actually 7 electrons in its outer level; ptcouncil.netmmand (group 4) has actually 4 electrons in its outer level.

Noble gases have ptcouncil.netmplete outer levels. This generalisation will certainly need editing and enhancing for A"level purposes.

Dots-and-crosses diagrams

In any kind of introductory chemistry ptcouncil.neturse you will have ptcouncil.netme throughout the digital structures of hydrogen and also carbon, because that example, attracted as:


Note: There are ptcouncil.netuntless places wherein you can still exploit this version of the atom at A"level. The is, however, a simplification and can it is in misleading. It gives the impression the the electrons space circling the nucleus in orbits like planets around the sun. As you will unptcouncil.netver when you look in ~ the A"level see of the atom, it is impossible to know precisely how they room actually moving.

The circles present energy level - representing increasing ranges from the nucleus. You ptcouncil.netuld straighten the circles out and draw the digital structure as a basic energy diagram.

Carbon, because that example, would certainly look like this:


Thinking of the plan of the electrons in this method makes a helpful bridge to the A"level view.

See more: 110 Cm In Feet And Inches ? Convert 110 Centimeters To Feet And Inches

Note: If you have pertained to this web page as a UK GCSE student (or a ptcouncil.netllege student on a ptcouncil.netmparable introductory chemistry food elsewhere) and want some an ext help, you might be interested in my GCSE Chemistry book. This attach will take you to a page describing it.