Atoms are made up of protons, neutrons, and electrons, with the balance of these particles determining the overall charge of an atom. When atoms gain or lose electrons, they become ions with positive or negative charges. The charge of an object affects how it reacts to its environment, and many everyday objects and processes make use of positive charges. The charges of atoms and molecules strongly influence their behavior and interactions, making them important in scientific research, particularly in rational drug design.
Everything in the world, natural or synthetic, is made up of tiny structures called atoms, which are made up of protons, neutrons and electrons. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. The balance of these particles determines the overall charge of an atom. An object with a positive charge, such as a person after rubbing their sock-covered feet vigorously on a carpet, contains more positive (protons) than negative (electrons) particles. Because positive atoms are attracted to negative ones and repelled by positive ones, the charges on the atoms that make up a piece of matter strongly influence its properties and behavior.
Atomic charges
Atoms, which are the basic unit of matter, have a nucleus made up of protons and neutrons, around which one or more electrons are bound. The number of protons determines which element the atom is and is given as the atomic number. For example, magnesium has 12 protons, giving it the atomic number 12, while oxygen has eight. When atoms join together, they become molecules.
Electrons and protons are not the same size and weight – electrons are smaller and lighter than protons – but they have the same amount of charge. That is, a corresponding number of protons and electrons cancel each other out in terms of overall charge. Since neutrons are neutral, their number does not affect the charge of an atom.
Although the total number of subatomic particles in an atom varies, atoms are generally electrically balanced, with equal numbers of protons and electrons. This means that, of course, atoms have a neutral charge, but this can change as they gain or lose electrons through chemical and physical processes. When an electron is lost, the balance shifts with an extra proton, giving the atom a positive charge. The converse is true for negatively charged atoms, which have gained an electron. When the equilibrium of particles is disrupted, producing a positive or negative atom (or molecule), they are no longer called atoms. Instead, they are ions, with positive ones called cations and negative ones called anions.
Charge and behavior
The charge an object has affects how it reacts to its environment. Cations are attracted to anions, for example, but are repelled by other cations. Similarly, negatively charged atoms repel each other. This behavior is referred to as Coulomb’s law.
Positive atoms do not attract or repel neutral ones, but through a phenomenon called electrostatic induction, an attraction can be created. This occurs because the electrons in some molecules tend to become more mobile when a positive charge is nearby. The electrons in the neutral molecule are then able to move towards the source of the positive charge. The motion creates a negative charge at the point closest to the source, although the molecule is unchanged overall. This phenomenon occurs most often with metals, which is what allows an electric charge to flow through them.
Everyday applications
Many everyday objects and processes make use of positive charges. When laundry falls into a dryer, for example, the motion causes electrons to move from atoms on the surface of some garments to others, giving the clothing items different charges. This is what leads to static electricity, as the now positively and negatively charged particles are attracted to each other and cause the clothes to stick together. Dryer sheets typically contain chemicals that have a positive charge, which rubs off onto items, helping to make negative ones neutral again.
Another example is the laser printer, which prints text and images on paper by creating a series of positive and negative charges. When a print job begins, the laser “writes” by transferring negatively charged static electricity to a positively charged cylinder. Toner, also positive, is then applied to the cylinder and is attracted to the negative areas. The cylinder is then rolled up on a sheet of negatively charged paper and the toner binds to it.
biological molecules
The combined total of all atoms and ions that are part of a biological molecule is known as its net charge. Most molecules are neutral overall, but large ones tend to have one or more discrete areas that display a negative or positive charge. These areas strongly influence how the molecule folds and how it interacts with other molecules. For example, DNA and RNA are both nucleic acids, but they behave very differently in part because their charges are distributed differently along their surfaces.
Scientific research often requires information on the charges of atoms and molecules because it influences the behavior of biologically active molecules. One particular area where manipulation of molecular charges is very useful is rational drug design. Researchers in this field work to develop more effective drugs, in some cases by manipulating the charge of a potential drug to make it interact more efficiently with its target.
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