This is the only naturally occurring fissile nucleus found on Earth although people have made other fissile isotopes of plutonium. In nature, uranium exists as a mixture of U, U, and U. The Energy education team has adapted the following simulation from the University of Colorado.
This simulation shows how neutrons and protons sit in energy levels and make up the nucleus. The number of neutrons and protons maintain particular ratios for the nucleus to be stable. Changing the number of neutrons in the nucleus changes the isotope.
Fossil Fuels. Nuclear Fuels. Acid Rain. Climate Change. Climate Feedback. Ocean Acidification. Rising Sea Level. Contact us About us Privacy policy Terms of use. The balance of 6 protons and 6 electrons makes the atom electrically neutral no charge.
Another version of carbon is C This version has 6 protons, 8 neutrons, and 6 electrons. The mass comes from adding the protons and neutrons. Since the number of protons and electrons is equal, the isotope has no charge. Why are isotopes electrically neutral? Apr 29, Explanation: Let's look at the example of carbon.
Theoretically, they would be more energetically stable if they followed the octet rule and had eight. Bohr diagrams : Bohr diagrams indicate how many electrons fill each principal shell. Group 18 elements helium, neon, and argon are shown have a full outer, or valence, shell. A full valence shell is the most stable electron configuration. Elements in other groups have partially-filled valence shells and gain or lose electrons to achieve a stable electron configuration. An atom may gain or lose electrons to achieve a full valence shell, the most stable electron configuration.
The periodic table is arranged in columns and rows based on the number of electrons and where these electrons are located, providing a tool to understand how electrons are distributed in the outer shell of an atom.
As shown in, the group 18 atoms helium He , neon Ne , and argon Ar all have filled outer electron shells, making it unnecessary for them to gain or lose electrons to attain stability; they are highly stable as single atoms. Their non-reactivity has resulted in their being named the inert gases or noble gases. In comparison, the group 1 elements, including hydrogen H , lithium Li , and sodium Na , all have one electron in their outermost shells.
This means that they can achieve a stable configuration and a filled outer shell by donating or losing an electron. As a result of losing a negatively-charged electron, they become positively-charged ions. Group 17 elements, including fluorine and chlorine, have seven electrons in their outermost shells; they tend to fill this shell by gaining an electron from other atoms, making them negatively-charged ions. When an atom gains an electron to become a negatively-charged ion this is indicated by a minus sign after the element symbol; for example, F-.
Electron orbitals are three-dimensional representations of the space in which an electron is likely to be found. Although useful to explain the reactivity and chemical bonding of certain elements, the Bohr model of the atom does not accurately reflect how electrons are spatially distributed surrounding the nucleus. They do not circle the nucleus like the earth orbits the sun, but are rather found in electron orbitals. These relatively complex shapes result from the fact that electrons behave not just like particles, but also like waves.
Mathematical equations from quantum mechanics known as wave functions can predict within a certain level of probability where an electron might be at any given time. The area where an electron is most likely to be found is called its orbital. The closest orbital to the nucleus, called the 1s orbital, can hold up to two electrons. This orbital is equivalent to the innermost electron shell of the Bohr model of the atom. It is called the 1s orbital because it is spherical around the nucleus.
The 1s orbital is always filled before any other orbital. Hydrogen has one electron; therefore, it has only one spot within the 1s orbital occupied. This is designated as 1s 1 , where the superscripted 1 refers to the one electron within the 1s orbital. Helium has two electrons; therefore, it can completely fill the 1s orbital with its two electrons.
This is designated as 1s 2 , referring to the two electrons of helium in the 1s orbital. On the periodic table, hydrogen and helium are the only two elements in the first row period ; this is because they are the sole elements to have electrons only in their first shell, the 1s orbital. The second electron shell may contain eight electrons. After the 1s orbital is filled, the second electron shell is filled, first filling its 2s orbital and then its three p orbitals.
When filling the p orbitals, each takes a single electron; once each p orbital has an electron, a second may be added. Lithium Li contains three electrons that occupy the first and second shells. Two electrons fill the 1s orbital, and the third electron then fills the 2s orbital. Its electron configuration is 1s 2 2s 1. Neon Ne , on the other hand, has a total of ten electrons: two are in its innermost 1s orbital, and eight fill its second shell two each in the 2s and three p orbitals.
Thus, it is an inert gas and energetically stable: it rarely forms a chemical bond with other atoms. Diagram of the S and P orbitals : The s subshells are shaped like spheres. Both the 1n and 2n principal shells have an s orbital, but the size of the sphere is larger in the 2n orbital.
Each sphere is a single orbital. Principal shell 2n has a p subshell, but shell 1 does not. Larger elements have additional orbitals, making up the third electron shell. Subshells d and f have more complex shapes and contain five and seven orbitals, respectively. Principal shell 3n has s, p, and d subshells and can hold 18 electrons. Principal shell 4n has s, p, d, and f orbitals and can hold 32 electrons.
Moving away from the nucleus, the number of electrons and orbitals found in the energy levels increases. Progressing from one atom to the next in the periodic table, the electron structure can be worked out by fitting an extra electron into the next available orbital.
While the concepts of electron shells and orbitals are closely related, orbitals provide a more accurate depiction of the electron configuration of an atom because the orbital model specifies the different shapes and special orientations of all the places that electrons may occupy. Chemical reactions occur when two or more atoms bond together to form molecules or when bonded atoms are broken apart. According to the octet rule, elements are most stable when their outermost shell is filled with electrons.
This is because it is energetically favorable for atoms to be in that configuration. However, since not all elements have enough electrons to fill their outermost shells, atoms form chemical bonds with other atoms, which helps them obtain the electrons they need to attain a stable electron configuration. When two or more atoms chemically bond with each other, the resultant chemical structure is a molecule. The familiar water molecule, H 2 O, consists of two hydrogen atoms and one oxygen atom, which bond together to form water.
Atoms can form molecules by donating, accepting, or sharing electrons to fill their outer shells. Atoms bond to form molecules : Two or more atoms may bond with each other to form a molecule. When two hydrogens and an oxygen share electrons via covalent bonds, a water molecule is formed. The substances used in the beginning of a chemical reaction are called the reactants usually found on the left side of a chemical equation , and the substances found at the end of the reaction are known as the products usually found on the right side of a chemical equation.
An arrow is typically drawn between the reactants and products to indicate the direction of the chemical reaction. For the creation of the water molecule shown above, the chemical equation would be:. An example of a simple chemical reaction is the breaking down of hydrogen peroxide molecules, each of which consists of two hydrogen atoms bonded to two oxygen atoms H 2 O 2. The reactant hydrogen peroxide is broken down into water H 2 O , and oxygen, which consists of two bonded oxygen atoms O 2.
In the equation below, the reaction includes two hydrogen peroxide molecules and two water molecules. This is an example of a balanced chemical equation, wherein the number of atoms of each element is the same on each side of the equation. According to the law of conservation of matter, the number of atoms before and after a chemical reaction should be equal, such that no atoms are, under normal circumstances, created or destroyed. Even though all of the reactants and products of this reaction are molecules each atom remains bonded to at least one other atom , in this reaction only hydrogen peroxide and water are representative of a subclass of molecules known as compounds: they contain atoms of more than one type of element.
Molecular oxygen, on the other hand, consists of two doubly bonded oxygen atoms and is not classified as a compound but as an element. Some chemical reactions, such as the one shown above, can proceed in one direction until the reactants are all used up. The equations that describe these reactions contain a unidirectional arrow and are irreversible.
Reversible reactions are those that can go in either direction. In reversible reactions, reactants are turned into products, but when the concentration of product goes beyond a certain threshold, some of these products will be converted back into reactants; at this point, the designations of products and reactants are reversed.
This back and forth continues until a certain relative balance between reactants and products occurs: a state called equilibrium. These situations of reversible reactions are often denoted by a chemical equation with a double headed arrow pointing towards both the reactants and products. If carbonic acid were added to this system, some of it would be converted to bicarbonate and hydrogen ions.
In biological reactions, however, equilibrium is rarely obtained because the concentrations of the reactants or products or both are constantly changing, often with a product of one reaction being a reactant for another. To return to the example of excess hydrogen ions in the blood, the formation of carbonic acid will be the major direction of the reaction.
However, the carbonic acid can also leave the body as carbon dioxide gas via exhalation instead of being converted back to bicarbonate ion, thus driving the reaction to the right by the chemical law known as law of mass action.
These reactions are important for maintaining the homeostasis of our blood. Interactive: What is a Chemical Reaction? Press run, then try heating and cooling the atoms to see how temperature affects the balance between bond formation and breaking. Ionic bonds are attractions between oppositely charged atoms or groups of atoms where electrons are donated and accepted. Some atoms are more stable when they gain or lose an electron or possibly two and form ions.
This results in a full outermost electron shell and makes them energetically more stable. Now, because the number of electrons does not equal the number of protons, each ion has a net charge. Cations are positive ions that are formed by losing electrons as the number of protons is now greater than the number of electrons.
Negative ions are formed by gaining electrons and are called anions wherein there are more electrons than protons in a molecule. For example, the anion of chlorine is called chloride, and the anion of sulfur is called sulfide. This movement of electrons from one element to another is referred to as electron transfer. As illustrated, sodium Na only has one electron in its outer electron shell. It takes less energy for sodium to donate that one electron than it does to accept seven more electrons to fill the outer shell.
When sodium loses an electron, it will have 11 protons, 11 neutrons, and only 10 electrons. It is now referred to as a sodium ion. Chlorine Cl in its lowest energy state called the ground state has seven electrons in its outer shell.
Again, it is more energy efficient for chlorine to gain one electron than to lose seven. Therefore, it tends to gain an electron to create an ion with 17 protons, 17 neutrons, and 18 electrons.
This gives it a net charge of -1 since there are now more electrons than protons. It is now referred to as a chloride ion. In this example, sodium will donate its one electron to empty its shell, and chlorine will accept that electron to fill its shell. Both ions now satisfy the octet rule and have complete outer shells. These transactions can normally only take place simultaneously; in order for a sodium atom to lose an electron, it must be in the presence of a suitable recipient like a chlorine atom.
Electron Transfer Between Na and Cl : In the formation of an ionic compound, metals lose electrons and nonmetals gain electrons to achieve an octet. In this example, sodium loses one electron to empty its shell and chlorine accepts that electron to fill its shell. Ionic bonds are formed between ions with opposite charges. For instance, positively charged sodium ions and negatively charged chloride ions bond together to form sodium chloride, or table salt, a crystalline molecule with zero net charge.
The attractive force holding the two atoms together is called the electromagnetic force and is responsible for the attraction between oppositely charged ions. Certain salts are referred to in physiology as electrolytes including sodium, potassium, and calcium. Electrolytes are ions necessary for nerve impulse conduction, muscle contractions, and water balance. Many sports drinks and dietary supplements provide these ions to replace those lost from the body via sweating during exercise.
Covalent bonds result from a sharing of electrons between two atoms and hold most biomolecules together. The octet rule can be satisfied by the sharing of electrons between atoms to form covalent bonds. These bonds are stronger and much more common than are ionic bonds in the molecules of living organisms. Covalent bonds are commonly found in carbon-based organic molecules, such as DNA and proteins.
One, two, or three pairs of electrons may be shared between two atoms, making single, double, and triple bonds, respectively. The more covalent bonds between two atoms, the stronger their connection.
Thus, triple bonds are the strongest. The strength of different levels of covalent bonding is one of the main reasons living organisms have a difficult time in acquiring nitrogen for use in constructing nitrogenous molecules, even though molecular nitrogen, N 2 , is the most abundant gas in the atmosphere.
Molecular nitrogen consists of two nitrogen atoms triple bonded to each other. The resulting strong triple bond makes it difficult for living systems to break apart this nitrogen in order to use it as constituents of biomolecules, such as proteins, DNA, and RNA.
The formation of water molecules is an example of covalent bonding. The hydrogen and oxygen atoms that combine to form water molecules are bound together by covalent bonds. The electron from the hydrogen splits its time between the incomplete outer shell of the hydrogen atom and the incomplete outer shell of the oxygen atom.
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