An atom containing one proton is a hydrogen atom H. An atom containing 6 protons is a carbon atom. And an atom containing 8 protons is an oxygen atom. The number of electrons that surround the nucleus will determine whether or not an atom is electrically charged or electrically neutral. The amount of charge on a single proton is equal to the amount of charge possessed by a single electron.
A proton and an electron have an equal amount but an opposite type of charge. Thus, if an atom contains equal numbers of protons and electrons, the atom is described as being electrically neutral. On the other hand, if an atom has an unequal number of protons and electrons, then the atom is electrically charged and in fact, is then referred to as an ion rather than an atom. Any particle, whether an atom, molecule or ion, that contains less electrons than protons is said to be positively charged.
Conversely, any particle that contains more electrons than protons is said to be negatively charged. In the previous section of Lesson 1 , an atom was described as being a small and dense core of positively charged protons and neutral neutrons surrounded by shells of negatively charged electrons.
The protons are tightly bound within the nucleus and not removable by ordinary measures. While the electrons are attracted to the protons of the nucleus, the addition of energy to an atom can persuade the electrons to leave an atom. Similarly, electrons within atoms of other materials can be persuaded to leave their own electron shells and become members of the electrons shells of other atoms of different materials.
In short, electrons are migrants - constantly on the move and always ready to try out a new atomic environment. All objects are composed of these atoms. The electrons contained within the objects are prone to move or migrate to other objects.
The process of an electron leaving one material object to reside perhaps only temporarily in another object is a common everyday occurrence. Even as you read the words of this web page, some electrons are likely moving through the monitor and adhering to your clothing assuming that you are using this resource online and wearing clothes.
If you were to walk across the carpeting towards the door of the room, electrons would likely be scuffed off the atoms of your shoes and moved onto the atoms of the carpet. And as clothes tumble in the dryer, it is highly likely that electrons on one piece of clothing will move from the atoms of the clothing onto the atoms of another piece of clothing.
In general, for electrons to make a move from the atoms of one material to the atoms of another material, there must be an energy source, a motive , and a low-resistance pathway. The cause and mechanisms by which this movement of electrons occurs will be the subject of Lesson 2.
For now, it is sufficient to say that objects that are charged contain unequal numbers of protons and electrons.
Charged objects have an imbalance of charge - either more negative electrons than positive protons or vice versa. And neutral objects have a balance of charge - equal numbers of protons and electrons. The principle stated earlier for atoms can be applied to objects. Objects with more electrons than protons are charged negatively; objects with fewer electrons than protons are charged positively.
In this discussion of electrically charged versus electrically neutral objects, the neutron has been neglected. When a dipolar molecule is exposed to an electric field, the molecule will align itself with the field, with the positive end towards the electric field and the negative end away from it. Ionic compounds are those that are formed from permanently charge-separated ions. Ions are still free from one another and will naturally move at random.
If they happen to move in a way that is asymmetrical, and results in a greater concentration of positive ions in one area and a greater concentration of negative ions in another, the sample of ionic compound will be polarized—a phenomenon is known as ionic polarization.
Electric charge is a physical property that is perpetually conserved in amount; it can build up in matter, which creates static electricity. Electric charge is a physical property of matter. The matter is positively charged if it contains more protons than electrons, and it is negatively charged if it contains more electrons than protons. In both instances, charged particles will experience a force when in the presence of other charged matter.
Charges of like sign positive and positive, or negative and negative will repel each other, whereas charges of opposite sign positive and negative will attract each another, as shown in.
Charge Repulsion and Attraction : Charges of like sign positive and positive, or negative and negative will repel each other, whereas charges of opposite sign positive and negative will attract each other.
The SI unit for charge is the Coulomb C , which is approximately equal to [latex]6. An elementary charge is the magnitude of charge of a proton or electron.
Charge, like matter, is essentially constant throughout the universe and over time. In physics, charge conservation is the principle that electric charge can neither be created nor destroyed.
The net quantity of electric charge, the amount of positive charge minus the amount of negative charge in the universe, is always conserved. For any finite volume, the law of conservation of charge Q can be written as a continuity equation:.
This does not mean that individual positive and negative charges cannot be created or destroyed. Electric charge is carried by subatomic particles such as electrons and protons, which can be created and destroyed.
For example, when particles are destroyed, equal numbers of positive and negative charges are destroyed, keeping the net amount of charge unchanged.
It can be created through contact between materials, a buildup of pressure or heat, or the presence of a charge. Static electricity can also be created through friction between a balloon or another object and human hair see. It can be observed in storm clouds as a result of pressure buildup; lightning see is the discharge that occurs after the charge exceeds a critical concentration.
Lightning : Lightning is a dramatic natural example of static discharge. All materials can be categorized as either insulators or conductors based on a physical property known as resistivity. An insulator is a material in which, when exposed to an electric field, the electric charges do not flow freely—it has a high resistivity.
Conversely, a conductor is a material that permits the flow of electric charges in one or more directions—its resistivity is low. All conductors contain electric charges that, when exposed to a potential difference, move towards one pole or the other. The positive charges in a conductor will migrate towards the negative end of the potential difference; the negative charges in the material will move towards the positive end of the potential difference.
This flow of charge is electric current. Ionic substances and solutions can conduct electricity, but the most common and effective conductors are metals. Copper is commonly used in wires due to its high conductivity and relatively inexpensive price. However, gold-plated wires are sometimes used in instances in which especially high conductivity is necessary.
Every conductor has a limit to its ampacity, or amount of current it can carry. This usually is the current at which the heat released due to resistance melts the material.
Insulators are materials in which the internal charge cannot flow freely, and thus cannot conduct electric current to an appreciable degree when exposed to an electric field. While there is no perfect insulator with infinite resistivity, materials like glass, paper and Teflon have very high resistivity and can effectively serve as insulators in most instances.
Just as conductors are used to carry electrical current through wires, insulators are commonly used as coating for the wires. Insulators, like conductors, have their physical limits. When exposed to enough voltage, an insulator will experience what is known as electrical breakdown, in which current suddenly spikes through the material as it becomes a conductor.
Conductor and Insulator in a Wire : This wire consists of a core of copper a conductor and a coating of polyethylene an insulator. The copper allows current to flow through the wire, while the polyethylene ensures that the current does not escape.
In , using charged droplets of oil, Robert Millikan was able to determine the charge of an electron. The Oil-Drop Experiment, otherwise known as the Millikan Oil-Drop Experiment, is one of the most influential studies in the history of physical science. Performed by Robert Millikan and Harvey Fletcher in , the experiment was designed to determine the charge of a single electron, otherwise known as the elementary electric charge. He used an atomizer to spray a mist of tiny oil droplets into a chamber, which included a hole.
Some droplets would fall through this hole and into a chamber, where he measured their terminal velocity and calculated their mass. However, each atom contains even smaller particles called electrons.
Electrons can move from one substance to another when objects are rubbed together. You may have done this with a party balloon: if you rub a balloon on your sweater, you can get the balloon to stick to the wall or to your hair.
This is because of static electricity. Positive ions are chemical species that carries a positive electrical charge. We call it a cation. These cations form when a neutral chemical species loses an electron from its chemical structure. Positive ions can be atoms or moieties of molecules. These species have protons and electrons in equal amounts in order to neutralize the charges. Therefore, when this atom or molecule loses an electron, there is an extra proton which has a positive charge.
This gives a net positive charge to the atom or molecule. Moreover, these ions are in several forms as monoatomic ions, diatomic ions or polyatomic ions according to the number of atoms present in the ionic species. Negative ions are chemical species which carries a negative electrical charge.
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