What is the maximum number of electrons?
We can use our understanding of quantum numbers to determine how atomic orbitals relate to one another after introducing the basics of atomic structure and quantum mechanics.We can determine which orbitals are occupied by electrons.Many of the chemical properties of an atom are determined by the arrangement of electrons in the atom.
As the principal quantum number increases, the energy of atomic orbitals increases.In an atom with two or more electrons, the repulsion between the electrons causes the energy of the subshells to be different.The lowest energy is represented by the 1s orbital at the bottom of the diagram.The increasing n value has more influence on energy than the increasing l value for small atoms as we move up to the 2s and then 2p, 3s, and 3p orbitals.This pattern doesn't work for larger atoms.The 3d orbital has more energy than the 4s.As we move up the chart, such overlaps occur frequently.
Low-energy orbitals are usually filled first by the electrons in successive atoms on the periodic table.The 5p orbitals fill immediately after the 4d, and immediately before the 6s, which is confusing to many students.The filling order has been confirmed by theoretical calculations.As the principal quantum number, n, increases, the size of the orbital increases and the electrons spend more time farther from the nucleus.The attraction to the nucleus is weaker and the energy associated with the orbital is less stable.There are other effects we have to take into account.As the value of l increases, the electrons are less penetrating in each shell.Shielding is a phenomenon that will be discussed in more detail in the next section.The higher the electron's energy, the less stable it is.The increase in energy due to n is more significant for small orbitals than it is for larger ones.Methods for remembering the order will be discussed.
The electron configuration of the atom is the arrangement of electrons in the orbitals of an atom.There is an electron configuration with a symbol that contains three pieces of information.
There are four electrons in a p subshell with a principal quantum number.There are eight electrons in the d subshell of the principal shell.
We can build structures in the order of atomic numbers to determine the electron configuration for any atom.We add one electron and one protons to the nucleus at a time until we describe the electron configurations of all the elements.The German word for "to build up" is the Aufbau principle.The added electron occupies the lowest energy available and is subject to the limitations imposed by the allowed quantum numbers.After lower-energy subshells have been filled to capacity, electrons enter higher- energy sub shells.The traditional way to remember the filling order for atomic orbitals is shown in Figure.
Figure (PageIndex4) provides an alternative method for determining the electron configuration since the periodic table arrangement is based on electron configurations.As you increase Z order, the filling order starts at hydrogen and includes each subshell.After filling the 3p block up to Ar, we can see the orbitals will be 4s and 3d.
The ground-state electron configuration and orbital diagram will be constructed for a selection of atoms in the first and second periods of the periodic table.Orbital diagrams are representations of the electron configuration.We start with a single hydrogen atom, which has one electron and one protons.We would expect to find the electron in the 1s orbital if we looked at either figure.The value is usually filled first.The electron configuration and the diagram are related.
The noble gas helium has an atomic number of 2.There are two protons and two electrons in the atom.The hydrogen atom electron has the same four quantum numbers as the first electron.The second electron fills the 1s orbital.The second electron has the same quantum numbers but has a different spin quantum number.The Pauli exclusion principle states that no two electrons can have the same set of four quantum numbers.Two arrows go in each box and the arrows must point in opposite directions.The diagram of the electron configuration of helium is below.
The atomic number of the next atom is 3.The first two electrons in lithium have the same set of four quantum numbers as the two in helium.The next lowest energy must be occupied by the remaining electron.The electron configuration and orbital diagram of lithium are.
Four protons and four electrons are present in an atom of the alkaline earth metal beryllium with an atomic number of 4.The remaining space in the 2s orbital is filled by the fourth electron.
Five electrons are contained in an atom of boron.The n shell is filled with two electrons and three electrons.The fifth electron must occupy the next energy level, which will be a 2p orbital, because any s subshell can only contain two electrons.The electron can occupy any of the three degenerate 2p orbitals.We include empty boxes to depict empty orbitals in the same subshell that we are filling.
Carbon has six electrons.The 1s and 2s are filled by four of them.Two electrons are in the 2p subshell.We have a choice of filling one of the 2p orbitals or leaving the electrons unpaired in two different, but degenerate, porbitals.The lowest-energy configuration for an atom with electrons within a set of degenerate orbitals is that having the maximum number of unpaired electrons.In accord with the Pauli exclusion principle, the two electrons in the carbon 2p orbitals have the same n, l, and ms quantum numbers.The diagram for carbon is:
Nitrogen fills the 1s and 2s subshells with one electron in each of the three 2p orbitals, in accordance with the rule of Hund.There are three electrons with unpaired spins.Oxygen has a pair of electrons in one of the 2p orbitals and a single electron in the other two.There is only one 2p orbital with an unpaired electron.The noble gas neon (atomic number 10) has all the electrons in pairs and all of the shells are filled.These four elements have electron configurations and orbital diagrams.
The neon atom has one less electron than the alkali metal.The electron must go into the lowest-energy subshell.There are two types of electrons: core electrons and valence electrons.We can shorten electron configurations by writing the noble gas that matches the core electron configuration along with the valence electrons in a Condensed format.The symbol Ne represents core electrons and our abbreviated configuration is Ne3s1.
The abbreviated configuration of lithium can be represented as [He]2s1, where he represents the same configuration as that of the filled inner shell.This way of writing the configurations emphasizes their similarity.Both atoms in the alkali metal family have one electron in a subshell outside of a filled set of inner shells.
The family member of the alkaline earth metal magnesium is itsatomic number 12.Outside of their filled inner shells, both atoms have a filled s subshell.It is similar to its family member boron, with 13 electrons and the electron configuration [He]2s22p1.
Except that the principal is carbon, nitrogen, oxygen, fluorine, and neon, the electron configurations of their outer shells are the same.Figure (PageIndex6) shows the lowest energy, or ground-state, electron configuration for these elements as well as that for atoms of each of the known elements.
We might expect to add electrons to the 3d subshell when we find the next element in the periodic table, the alkali metal potassium.The chemical and physical evidence shows that the next electron is added to the 4s level instead of the 3d level.The 3d orbital with no radial nodes is more energy efficient than the 4s because it is less penetrating and more shielded from the nucleus.There is an electron configuration of [Ar]4s1.In its shell configuration, Li and Na are related.The calcium has an electron configuration of [Ar]4s2 and the next electron is added to complete the 4s subshell.The outer-shell electron configuration of calcium is similar to that of magnesium and beryllium.
Additional electrons are added to the 3d subshell after the transition metal scansdium.There are five d orbitals with a combined capacity of 10 electrons in this subshell.Next, the 4p subshell fills.A total of 10 d electrons are added to the shell next to each of the elements.For two series, lanthanum through lutetium and actinium through lawrencium, 14 f electrons with a combined capacity of 7 ml values.
What is the orbital diagram for a phosphorus atom?What are the four numbers for the last electron added?
The number 15 is the atomic number of phosphorus.There are 15 electrons in a phosphorus atom.The order of filling the energy levels is 1...The 3p orbital contains three electrons and the 15 electrons of the phosphorus atom.
A 3p electron is the last electron added.For a p-type orbital, n is 3 and l is 1.The value could be negative or positive.Any of these values are correct because of the three p orbitals.The value of (+dfrac12) is assigned to the spin quantum number for unpaired electrons.
Predicting the electron configuration of an element can be done with the periodic table.There are exceptions to the order of filling that are shown in Figure.The electron configurations of the transition metals are not what we would expect.Small effects can lead to changes in the order of filling if the exceptions involve subshells with very similar energy.
We found that the conditions of preferred stability were represented by half-filled and completely filled subshells.The extra stability of a half-filled 3d subshell can be obtained by shifting an electron from the 4s into the 3s.There are also other exceptions.Niobium (Nb, atomic number 41) is predicted to have an electron configuration.The ground-state electron configuration is actually [Kr]5s14d4.The gap in energy between the 5s and 4d orbitals is larger than the electron–electron repulsions experienced by pairs of electrons.There is no simple method to predict the exceptions for atoms where the magnitude of the repulsions between electrons is greater than the small differences in energy between subshells.
The periodic table arranges atoms based on increasing atomic number so that elements have the same chemical properties.We can see a periodic recurrence of similar electron configurations in the outer shells of these elements when they are added to the table.The most important role in chemical reactions is played by valence electrons, who are in the outer shells of an atom.The outer electrons have the highest energy of the electrons in an atom and are more easily lost or shared than the core electrons.Some physical properties of the elements are determined by valence electrons.
The elements in any one group all have the same number of valence electrons.The number of valence electrons in elements of the same group leads to similarity in chemical properties.The loss, gain, or sharing of electrons is what defines how elements react.
The periodic table was developed based on the chemical behavior of the elements, before any idea of their atomic structure was available.The periodic table has an arrangement in which elements have the same number of electrons in their nucleus.In Figure (PageIndex6), the electron configuration of the last subshell is shown in periodic-table form.The main group, transition, and inner transition elements are shown in the colored sections of Figure.The highest energy level orbitals of an atom are counted by these classifications.
Even though they are transition metals with no f electrons, Lanthanum and actinium are included and used to name the series.
When atoms gain or lose electrons, they form an ion.A positively charged ion forms when electrons are removed from a parent atom.The first electrons are removed from the main group elements.The electrons in the s orbital are easier to remove than the d or f electrons, and so the highest ns electrons are lost.An anion is formed when one or more electrons are added to a parent atom.The added electrons fill the order predicted by the principle.
Write out the configuration of the parent atom.We have chosen to show the full, unabbreviated configurations to provide more practice for students who want it.
Determine if an electron is gained or lost.ion with a positive charge have lost an electron.The last orbital gains or loses an electron for main group elements.The last s orbital loses an electron before the d orbitals.