What are the key learning points about atomic structure?
There have been a number of ideas over time about the structure of The smallest particle of an element. We often think of atoms as tiny spheres, but in fact they are made from smaller particles called protons, neutrons and electrons..
Atoms are made up of Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1., Uncharged subatomic particle, with a relative mass of 1. The relative charge of a neutron is 0 (neutral). and Subatomic particle, with a negative charge and a very small mass relative to protons and neutrons., which each have different masses and charges.
An A pure substance which is made from only one type of atom. Elements are listed on the periodic table. An element cannot be broken down into anything simpler by chemical means. is made up of one type of atom.
What are atoms?
All matter is made of atoms.
The word “atom” is derived from the ancient Greek word atomos – meaning “something that cannot be divided”.
What is the modern atomic model?
Today, scientists use an atomic model that has a central, positively-charged The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei. that contains:
positively-charged Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1.,
neutral Uncharged subatomic particle, with a relative mass of 1. The relative charge of a neutron is 0 (neutral)..
Negatively-charged Subatomic particle, with a negative charge and a very small mass relative to protons and neutrons. The path that electrons take as they move around the nucleus. the nucleus in shells.
An atom’s nucleus gives it most of its mass.
What mass are protons, neutrons and electrons? (Higher tier only)
The The relative mass is the number of times heavier a particle is, compared to another., relative charge and location in the atom for each Objects found in atoms, including protons, neutrons and electrons. is given in the table.
| Subatomic particle | Relative mass | Relative charge | Location in atom |
|---|---|---|---|
| Proton | 1 | +1 | In nucleus |
| Neutron | 1 | 0 | In nucleus |
| Electron | \(\frac{1}{1840}\) | -1 | In shells orbiting the nucleus |
What is the atomic number and mass number?
An atom’s atomic number is the number of protons in its nucleus.
Atomic number = number of protons.
An atom’s mass number is the total number of protons and neutrons.
Mass number = number of protons + number of neutrons.
What is the electrical charge of an atom? (Higher tier only)
An atom has no overall charge, because it has an equal number of protons and electrons.
An atom’s nucleus gives it most of its mass.
Test your knowledge
See if you can identify parts of the atom.
How to calculate the number of protons, neutrons and electrons
When we write the symbol for an atom, we can place its The total number of protons and neutrons found in the nucleus of an atom. at the top left and its The number of protons in the nucleus of an atom. at the bottom left.
You can use these numbers to calculate the number of Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1., Uncharged subatomic particle, with a relative mass of 1. The relative charge of a neutron is 0 (neutral). and Subatomic particle, with a negative charge and a very small mass relative to protons and neutrons. in an The smallest particle of an element. We often think of atoms as tiny spheres, but in fact they are made from smaller particles called protons, neutrons and electrons..
Number of protons = number of electrons = atomic number
Number of neutrons = mass number – atomic number
Key fact
Remember that protons are positive, and neutrons are neutral.
Question
The atomic number of a sodium atom is 11 and its mass number is 23.
Calculate the number of protons, neutrons and electrons it contains.
Answer
Number of protons = 11
Number of electrons = 11
Number of neutrons (mass number - atomic number) = 23 - 11 = 12
Question
The box below shows how fluorine appears on the periodic table.
Use the information in the box to calculate the number of protons, neutrons and electrons in an atom of fluorine.
Answer
Atomic number = 9, mass number = 19
Number of protons = atomic number = 9
Number of neutrons = mass number - atomic number = 19 - 9 = 10
Number of electrons = number of protons = atomic number = 9
What is electronic configuration?
Electronic configuration, electronic structure and electronic arrangement all mean the same thing.
Subatomic particle, with a negative charge and a very small mass relative to protons and neutrons. The path that electrons take as they move around the nucleus. the The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei. in An energy level around the nucleus where electrons can be found orbiting..
- Each shell is at a different distance from the nucleus. The first shell is nearest to the nucleus.
- Different shells hold a different maximum number of electrons.
- The electrons fill the lowest available shell first – the one nearest the nucleus.
- When this shell is full, the electrons begin to fill the next shell.
The table below shows the maximum number of electrons each shell can hold for elements with atomic numbers 1 to 20.
| Shell | Maximum electrons |
|---|---|
| First | 2 |
| Second | 8 |
| Third | 8 |
| Fourth | 2 |
How to write and draw electronic configuration
Take sodium as an example.
Sodium has 11 electrons.
It has:
- 2 electrons in the first shell,
- 8 electrons in the second shell,
- 1 electron in the third shell.
You can write sodium’s electronic configuration with numbers and commas: 2,8,1
The electronic configuration of sodium can be shown in a diagram.
The dots represent electrons.
Electrons may be shown using dots or crosses.
Key fact
When drawing electrons in the second or third shell, the first four electrons should be drawn spread out, then the remaining four electrons ‘pair-up’ with the first four.
Question
An atom of oxygen has 8 electrons.
Write the electron configuration of an oxygen atom, and show the configuration in a diagram.
Answer
- 2 electrons in the first shell.
- 6 electrons in the second shell.
The electron configuration of an oxygen atom is 2,6.
How much do you know about atomic structure?
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