Electron shells & orbitals | The periodic table (article) | Khan Academy
An atom with a closed shell of valence electrons (corresponding to an is highly reactive, because the extra valence electrons are easily removed to form a in explaining the molecular structure of many organic compounds. The number of electrons in an atom's outermost valence shell governs its bonding behaviour. That fact makes the valence electrons more likely to interact with other atoms. The valence are also That way, we can get a better look at the relationship. Can you explain why the electronegativity increases as atomic number increases ?.
- 1.3: Valence electrons and open valences
- How do valence electrons affect reactivity?
- The periodic table, electron shells, and orbitals
Therefore, elements whose atoms can have the same number of valence electrons are grouped together in the periodic table of the elements. As a general rule, a main group element except hydrogen or helium tends to react to form a closed shellcorresponding to the electron configuration s2p6. This tendency is called the octet rulebecause each bonded atom has eight valence electrons including shared electrons.
The most reactive kind of metallic element is an alkali metal of group 1 e. An alkaline earth metal of Group 2 e. Within each group each periodic table column of metals, reactivity increases with each lower row of the table from a light element to a heavier elementbecause a heavier element has more electron shells than a lighter element; a heavier element's valence electrons exist at higher principal quantum numbers they are farther away from the nucleus of the atom, and are thus at higher potential energies, which means they are less tightly bound.
How do valence electrons affect reactivity? + Example
A nonmetal atom tends to attract additional valence electrons to attain a full valence shell; this can be achieved in one of two ways: An atom can either share electrons with a neighboring atom a covalent bondor it can remove electrons from another atom an ionic bond. The most reactive kind of nonmetal element is a halogen e. Such an atom has the following electron configuration: To form an ionic bond, a halogen atom can remove an electron from another atom in order to form an anion e.
To form a covalent bond, one electron from the halogen and one electron from another atom form a shared pair e. Within each group of nonmetals, reactivity decreases with each lower rows of the table from a light element to a heavy element in the periodic table, because the valence electrons are at progressively higher energies and thus progressively less tightly bound.
In fact, oxygen the lightest element in group 16 is the most reactive nonmetal after fluorine, even though it is not a halogen, because the valence shell of a halogen is at a higher principal quantum number.
The shell closest to the nucleus, 1n, can hold two electrons, while the next shell, 2n, can hold eight, and the third shell, 3n, can hold up to eighteen. The number of electrons in the outermost shell of a particular atom determines its reactivity, or tendency to form chemical bonds with other atoms.
This outermost shell is known as the valence shell, and the electrons found in it are called valence electrons. In general, atoms are most stable, least reactive, when their outermost electron shell is full. Most of the elements important in biology need eight electrons in their outermost shell in order to be stable, and this rule of thumb is known as the octet rule. Some atoms can be stable with an octet even though their valence shell is the 3n shell, which can hold up to 18 electrons.
We will explore the reason for this when we discuss electron orbitals below. Examples of some neutral atoms and their electron configurations are shown below. In this table, you can see that helium has a full valence shell, with two electrons in its first and only, 1n, shell.
Similarly, neon has a complete outer 2n shell containing eight electrons. These electron configurations make helium and neon very stable.
Although argon does not technically have a full outer shell, since the 3n shell can hold up to eighteen electrons, it is stable like neon and helium because it has eight electrons in the 3n shell and thus satisfies the octet rule. In contrast, chlorine has only seven electrons in its outermost shell, while sodium has just one. Remember, that corresponds to the "valence shell". Think of electrons as forming layers around the nucleus. Electrons with principal quantum number one form a first layer.
Those with principal quantum number 2 form a second layer, and so on. Each layer is further away from the nucleus. Remember, electrostatic attraction gets weaker as charges get further away from each other. As electrons get further from the nucleus, they are less tightly held. Moving down a column in the periodic table, valence electrons are held less tightly because they get further from the nucleus.
Electronegativity decreases as we move down a column in the periodic table. We can see this general size trend in the following periodic table. This table presents covalent radii, which are related to the sizes of the atoms although not exactly the same; data on atomic radii are not available for all atoms, however.
Covalent radii of the atoms. Download a copy here. We can clearly see the expanding radii of atoms if we look at Group 1, the first column; these elements are called the alkali metals.
Hydrogen, at the top, is very small. Lithium is much bigger. Sodium is much bigger than lithium, however, and potassium is much bigger than sodium. Each time an electron is added to an orbital that is significantly farther from the nucleus, of course it is going to result in a bigger atom.
Remember, the atom is mostly empty space, and its size is described by the outermost reaches of its electrons. So when we go to the next principal quantum number -- that is, to the next row in the periodic table, from the first row to the second row, for example -- the next electron is much further away from the nucleus.
It has to be that way, because electrons repel each other. They can't all be equally close to the nucleus, because there would be too much repulsion. Instead, they form these layers, and when the first layer is so full that there would be too much repulsion if anothe relectron were added, we start the next layer.
Of course, the very first layer is very, very small. There just isn't that much room so close to the nucleus.
Valence electrons and open valences - Chemistry LibreTexts
For the first row, only two electrons are allowed. Then they have to start the next layer. For the second row, eight electrons are allowed; that's the origin of something called the "octet rule" think "octopus" for common compounds, which you'll see later on. Eventually we get to eighteen electrons in a shell, then thirty two, as the shells get bigger and bigger like layers of an onion, or like nested Russian dolls. There is another important trend if you look carefully. As you move from left to right across the periodic table, from one group to the next, the atoms get bigger.
That doesn't make any sense, does it? If we are adding more electrons, why would the atom get smaller? The key thing is, not only are we adding more electrons, but we are also adding more protons in the nucleus.
The new electrons we are adding are all roughly equidistant from the nucleus; they are all equally close to the protons. So as the charge on the nucleus gets bigger, those electrons are all more strongly attracted to the centre. Eventually, we get to the point at which we couldn't possibly add more electrons; the radius has shrunk so much that repulsion would become too great if we added one more electron.
Then we just start another row. Just before that point, however, we hit a sweet spot: This last column in the table contains the noble gases, which are particularly stable and unreactive. Why does electronegativity fall so sharply between hydrogen and lithium, and much more subtly between lithium and sodium? Which atom, in the following pairs, is more electronegative? Electron ionization is the energy that must be added in order to pull an electron away from an atom.
What is holding the electron there? The ionization energies of the second row elements.
1 what is the relationship between the valence electrons of an atom and its chemical reactivity?
Sometimes a plot of the data can be revealing. Ionization energies do not follow a smooth trend.
Explain why it is a little easier to remove an electron from boron and oxygen than expected. Electron configurations may be helpful here.
Plot of the ionization energies of the second row elements. Explain the trend in the following data on ionization energy.
The ionization energies of the alkali elements. Electron affinity is the energy released when a free electron is picked up by an atom. The electron affinities of the alkali elements. Why do beryllium and neon have such low electron affinities almost zero? Usually, elements become bigger as we go down a column in the periodic table. However, in a phenomenon called "the lanthanide contraction", some elements are actually smaller than the ones in the row above them.
Specifically, osmium, iridium, platinum, gold, and mercury are smaller than their relatives, ruthenium, rhodium, palladium, silver, and cadmium, respectively.
Use the periodic table in Figure AT6.