Atomos is an ancient Greek word meaning 'indivisible' or 'cannot be cut'. Atoms are the building blocks of matter; they are the smallest particles that when combined together have the properties of a particular chemical element, or compound.

In this section you will find answers to questions such as the following:

What's in an Atom?

Protons, neutrons and electrons are sub-atomic particles that together make up atoms. Protons and neutrons are found in the centre (nucleus) of an atom and electrons are found in the space around the nucleus. Read more: The nuclear atom

What are mass and charge of a proton, neutron and electron?

Protons are positively charged, and have a mass of 1 unit; neutrons are neutral and have a mass of 1 unit; electrons are negatively charged and have negligible mass. See the revision cards: The nuclear atom

What's the definition of an isotope?

Isotopes are atoms of the same element (same number of protons) with a different mass number (different number of neutrons). See the revision cards: The nuclear atom

What does a mass spectrum show?

A mass spectrum is a chart showing the mass numbers of chemical species (atoms, molecules, fragments of molecules; all of which have been turned into ions so that they can be detected). Read more: The nuclear atom and Spectroscopic identification I

What does Bohr's model explain?

The Bohr model shows electrons in shells (or energy levels) around the nucleus with the number of electrons in the outermost shell matching the main group number (old Roman numerals) on the periodic table. Watch the video:  Electron configuration

What is the quantum mechanical model of the atom?

The quantum mechanical model of the atom is a development of the Bohr model, showing the electrons in energy levels, but also showing finer detail with the electrons in sub-levels and orbitals. The quantum mechanical model of the atom is reflected in the arrangement of elements in the periodic table! Watch the videos:  Electron configuration

What is an orbital in chemistry?

A three-dimensional space in which a maximum of two electrons may be found. Read more:  Electron configuration

What is the emission spectrum of hydrogen?

The emission spectrum of hydrogen is a line spectrum − showing specific frequencies of light − indicating the energy associated with particular transitions (movement) of electrons between energy levels. The spectrum provides evidence for the quantum mechanical model of the atom. Watch the video:  Electron configuration

What is first ionisation energy?

First ionisation energy for the an atom of an element is an indication of the energy needed to remove the outermost electron in the atom (more specifically one electron from every atom in one mole of atoms in the gas phase). So first ionisation energies tell us the relative energies of electrons; that is the energy of the orbital, sub-level and energy level in which the electron sits. Watch the video:  Electron configuration

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  Periodic table