Despite the discovery of sub-particles like electrons, protons and neutrons, an atom continues to remain the fundamental particle because of the fact that it is the smallest unit human can calculate and model that exhibits the chemical properties of an element. Chemistry is essentially the study of matter and the changes it undergoes in everyday activities like cooking to more complex processes such as photosynthesis.

In essence, the heart of chemistry involves studying changes around our world. Let us discuss some basic ideas of atoms, molecules and the matter they make--elements and compounds. As stated earlier, an atom is the smallest constituent particle of an element which exhibits the chemical properties of an element and also can take part in a chemical reaction.

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Atoms are extremely small and their sizes are about an angstrom. Initial studies showed that it is spherical in shape. However, the recent quantum mechanical model, which today is widely accepted, suggests that it does not have a fixed shape or structure. For representative purposes and convenience, we however assume it to be spherical.

This is due to the uncertainty principle, as proven by Werner Von Heisenberg, popularly known as Heisenberg uncertainty principle. The word "atom" has a Greek origin from the verb "temnein" meaning "to cut. When Dalton gave his atomic theory, it was believed that atom was indivisible and hence the name. But later it was found that atoms have been subdivided into simpler parts.

These simpler parts are called the subatomic particles. Based on the standard atomic model, there are 12 fermions having fractional spin , 4 gauge bosons having complete integer spin , and the Higgs boson. There are 6 flavors meaning types, but in the language of quantum mechanics, flavors quarks and their counterparts in antimatter. But the discussion of antimatter is not a subject here. The quarks, when bound by gluons read on to find out what they are , form hadrons.

The most stable hadrons are protons and neutrons. The smaller the quark, the more mass it has. There are 3 generations of quarks:. These include the strange quark and the charm quark. They quickly decay into the -generation quarks. There are electrons, muons, tauon, electron neutrino, muon neutrino, and tau neutrino. All leptons have a spin of.

## Atoms, elements and compounds - AQA

The leptons that are not neutrinos have a charge of Neutrinos have a charge of 0. Bosons are any particle that follows Bose-Einstein statistics. Bosons in the standard model are photons, gluons, Z bosons, and W bosons.

The photon carries electromagnetic radiation. The gluon carries the strong force. All bosons have an integer spin. The Higgs boson has 0 spin and even parity. The amount of interaction is called mass.

## Introduction to chemistry (video) | Khan Academy

Thomson laid the fundamental concept of the structure of the atom. He referred to it as the plum pudding model , in which the nuts showed the negatively charged particles. This model had serious drawbacks; it was proved that this was a wrong concept by the next model as it couldn't explain the results of the gold foil experiment carried out by Ernest Rutherford in He conducted a very famous experiment, the gold foil experiment.

In this experiment, he bombarded alpha particles on a thin gold foil.

Moreover, he thought that matter was composed of atoms, in which there was no space. Imagine it like a row of marbles, one next to the other. With this idea in mind, all alpha particles should bounce back. Astonishingly, only one out of every -particles bounced back. And very few got deflected by some angles. So he concluded that. But later his second conclusion was not accepted, because if the electrons revolve in a circular motion, they must spend energy and finally will fall into the nucleus, which means the atoms will be unstable.

After a few years, Niels Bohr came up with a new model explaining the stability correctly. Although this model got the basics right, there are fundamental problems with it. For one, it doesn't explain why there are only 2 electrons in the K-level. Quantum mechanical models are the modern concept to explain the structure of atoms and describe the state of electrons in an atom in terms of probability of finding electrons in the space around the nucleus. This leads to the concept of orbitals.

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It is defined as "the three-dimensional region in space around the nucleus where the probability of finding the electron is maximum. The classical concept of orbits, like planets revolving a sun, for example, is given up in the quantum mechanical description of the atomic world. We only know where there is a high chance that the electron is to be found. We can no longer pinpoint the position of the electron nor the proton nor the neutron Thus the orbitals are the region where the probability of finding an electron is high. This idea radically changes our view, to the extent that even Einstein himself doubted the model.

He was willing to consider it a correct, yet incomplete model. The fundamental notion that we can only statistically gain information about quantum mechanical properties is a radical thought changer from the deterministic view Newton used to uphold. Even the theory of relativity is utterly deterministic.

However, all experiments conducted so far strengthen the quantum mechanical and we even have strong reasons to believe the great master himself was wrong in his doubting. Finally after much debates Bohr's model was accepted as the universal model. Let's now look into the final structure and the parts of an atom.

There are mainly three subatomic particles--the electron, the proton, and the neutron. The protons and the neutrons together form the nucleus and are thus called the nucleons.

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The protons are positively charged and carry a charge of , while the neutrons do not have any charge. The electrons , on the other hand, are negatively charged. Every sodium atom has 11 protons and 11 electrons. It has 11 positive charges and 11 negative charges. Atoms of different elements usually have different mass numbers , but they can be the same. For example, the mass number of argon atoms and calcium atoms can both be The symbol for an atom can be written to show its mass number at the top, and its atomic number at the bottom.

To calculate the numbers of subatomic particles in an atom, use its atomic number and mass number: The atomic number of a sodium atom is 11 and its mass number is