Build an atom: protons, neutrons and electrons
Add protons, neutrons and electrons and watch an atom appear: the element, its isotope, its ion charge, the electron shells and the electron configuration. Free for every student.
Also searched as: atom · build an atom simulation · structure of atom class 11 · protons neutrons and electrons · atomic number and mass number · isotopes and ions
About this experiment
| Subject | Chemistry |
|---|---|
| Class | 11 |
| Unit | 2. Structure of Atom |
| NCERT section | 2.1–2.6 |
| Level | NCERT level |
| Time | about 15 minutes |
| Access | Free, no card needed |
Aim
To build atoms, isotopes and ions from protons, neutrons and electrons, and to see how the numbers decide the element, the mass number, the charge and the arrangement of electrons in shells.
Theory
An atom has a tiny, heavy nucleus in the centre and electrons moving around it. The nucleus holds protons (positive charge, mass about 1 u) and neutrons (no charge, mass about 1 u). An electron has a negative charge and a mass of only 1/1836 u, so almost all the mass of an atom is in the nucleus.
The number of protons is the atomic number Z. It decides which element the atom is: 6 protons is always carbon, 8 protons is always oxygen. The mass number A is the number of protons plus neutrons: A = Z + N.
Atoms of the same element with a different number of neutrons are isotopes. Carbon-12 has 6 neutrons and carbon-14 has 8. They have the same chemical properties (same electrons) but a different mass, and some of them are radioactive.
Formulas used
- Z = number of protons = number of electrons in a neutral atom
- A = Z + N (mass number = protons + neutrons)
- charge = Z − number of electrons
- maximum electrons in shell n = 2n²
- subshell capacity: s = 2, p = 6, d = 10
- filling order: 1s 2s 2p 3s 3p 4s 3d 4p
Procedure: what to do in the virtual lab
- Set 1 proton, 0 neutrons: this is hydrogen. Add one proton at a time up to 10 and watch the name change.
- Set 6 protons and 6 neutrons (carbon-12). Now change the neutrons to 8 (carbon-14) and see that the element stays the same but the nucleus becomes radioactive.
- Take sodium (11 protons, 12 neutrons) and set the charge to +1. One electron leaves the third shell: this is Na⁺ with the electrons of neon.
- Take chlorine (17 protons) and set the charge to −1. The third shell becomes full: Cl⁻ has the electrons of argon.
- Go to 19 protons (potassium) and 24 (chromium): check where the 4s electron goes.
Observations to make
- The element name depends only on the number of protons, never on neutrons or electrons.
- Elements in the same column of the periodic table have the same number of outer electrons (for example Li, Na and K have 1).
- Ions of different elements can have the same electron arrangement (Na⁺, Mg²⁺, F⁻, O²⁻ all have the neon arrangement 2, 8).
- The nucleus is drawn much bigger than it really is. If the nucleus were a marble, the electrons would be about a kilometre away.
What you can change in this experiment
- Protons in the nucleus (atomic number Z)
- Neutrons in the nucleus
- Charge of the particle (+ lost electrons, − gained electrons)
- Electrons moving (on / off)
Viva questions on Build an atom
Questions an examiner may ask in the Class 11 chemistry practical. Run the experiment in the lab to find the answers yourself, then check them in the Learn tab.
- What is the difference between atomic number and mass number?
- What are isotopes? Give an example.
- Why is an atom electrically neutral?
- How many electrons does Mg²⁺ have, and which noble gas has the same arrangement?
- What is the maximum number of electrons in the M shell?
Frequently asked questions
What is the aim of the Build an atom experiment?
To build atoms, isotopes and ions from protons, neutrons and electrons, and to see how the numbers decide the element, the mass number, the charge and the arrangement of electrons in shells.
Which formulas are used in the Build an atom experiment?
Z = number of protons = number of electrons in a neutral atom; A = Z + N (mass number = protons + neutrons); charge = Z − number of electrons; maximum electrons in shell n = 2n²; subshell capacity: s = 2, p = 6, d = 10
What viva questions are asked on Build an atom?
What is the difference between atomic number and mass number? What are isotopes? Give an example. Why is an atom electrically neutral? How many electrons does Mg²⁺ have, and which noble gas has the same arrangement?
How do I do the atom experiment for Class 11 online?
Open the Build an atom virtual lab on PractiSci, follow the procedure above, change the values and read the live graph. It matches the Class 11 chemistry practical, with the aim, theory, observations and viva questions on this page.
Can I do the Build an atom experiment online?
Yes. Open it as a 3D virtual lab in your browser or on your phone, change the values and read the results from live graphs. This lab is free.
Syllabus: Class XI Chemistry, Chapter 2 — Structure of Atom, §2.1–2.6
What you do in the lab
Change the controls and watch the chemistry behave in real time in 3D. Live readouts and graphs show the numbers behind it, and the Learn tab has the theory, procedure, observations and viva questions. Works on a phone or a laptop, in English and Hindi.
Topics: atom · proton · neutron · electron · isotope · ion · electron configuration · atomic number · mass number · structure of atom
More from this unit
- Electron clouds: shapes of s, p and d orbitals in 3D
- Schrödinger wave equation: wave function, probability and quantised energy
- Electron, proton and neutron: how they were discovered (beams in electric and magnetic fields)
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