Section 1
Atoms, Isotopes, Ions, and Molecules
By Boundless
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Atoms are made up of particles called protons, neutrons, and electrons, which are responsible for the mass and charge of atoms.
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The atomic number is the number of protons in an element, while the mass number is the number of protons plus the number of neutrons.
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Isotopes are various forms of an element that have the same number of protons, but a different number of neutrons.
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Everything in the universe is made of one or more elements. The periodic table is a means of organizing the various elements according to similar physical and chemical properties.
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Niels Bohr proposed an early model of the atom as a central nucleus containing protons and neutrons being orbited by electrons in shells.
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Electron orbitals are three-dimensional representations of the space in which an electron is likely to be found.
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Chemical reactions occur when two or more atoms bond together to form molecules or when bonded atoms are broken apart.
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Ionic bonds are attractions between oppositely charged atoms or groups of atoms where electrons are donated and accepted.
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Covalent bonds result from a sharing of electrons between two atoms and hold most biomolecules together.
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Hydrogen bonds and van der Waals interactions are two types of weak bonds that are necessary to the basic building blocks of life.