Although it is said that atoms share electrons when they form covalent bonds, they do not usually share the electrons equally. Only when two atoms of the same element form a covalent bond are the shared electrons actually shared equally between the atoms.
When atoms of different elements share electrons through covalent bonding, the electron will be drawn more toward the atom with the higher e lectronegativity resulting in a polar covalent bond.
When compared to ionic compounds, covalent compounds usually have a lower melting and boiling point, and have less of a tendency to dissolve in water. Covalent compounds can be in a gas, liquid, or solid state and do not conduct electricity or heat well.
The types of covalent bonds can be distinguished by looking at the Lewis dot structure of the molecule. For each molecule, there are different names for pairs of electrons, depending if it is shared or not. A pair of electrons that is shared between two atoms is called a bond pair. A pair of electrons that is not shared between two atoms is called a lone pair.
The Octet Rule requires all atoms in a molecule to have 8 valence electrons--either by sharing, losing or gaining electrons--to become stable. For Covalent bonds, atoms tend to share their electrons with each other to satisfy the Octet Rule.
It requires 8 electrons because that is the amount of electrons needed to fill a s - and p - orbital electron configuration ; also known as a noble gas configuration. Each atom wants to become as stable as the noble gases that have their outer valence shell filled because noble gases have a charge of 0. Although it is important to remember the "magic number", 8, note that there are many Octet rule exceptions.
Example: As you can see from the picture below, Phosphorus has only 5 electrons in its outer shell bolded in red. Argon has a total of 8 electrons bolded in red , which satisfies the Octet Rule. Phosphorus needs to gain 3 electrons to fulfill the Octet Rule. It wants to be like Argon who has a full outer valence shell. A single bond is when two electrons--one pair of electrons--are shared between two atoms.
It is depicted by a single line between the two atoms. Although this form of bond is weaker and has a smaller density than a double bond and a triple bond, it is the most stable because it has a lower level of reactivity meaning less vulnerability in losing electrons to atoms that want to steal electrons.
Below is a Lewis dot structure of Hydrogen Chloride demonstrating a single bond. As we can see from the picture below, Hydrogen Chloride has 1 Hydrogen atom and 1 Chlorine atom.
Hydrogen has only 1 valence electron whereas Chlorine has 7 valence electrons. To satisfy the Octet Rule, each atom gives out 1 electron to share with each other; thus making a single bond. Such species are called ions. Solubility can be altered by manipulating temperature. Typically, many insoluble compounds can be dissolved at higher temperatures. Because most filled electron shells have eight electrons in them, chemists called this tendency the octet rule.
However, there is another way an atom can achieve a full valence shell: atoms can share electrons. This type of bonding would be a covalent bond. However, there are a few stable molecules which contain an odd number of electrons.
These molecules, called "free radicals", contain at least one unpaired electron, a clear violation of the octet rule. Free radicals play many important roles a wide range of applied chemistry fields, including biology, medicine, and environmental chemistry.
How many valence electrons are in a silicon atom? How many valence electrons are in an atom of chlorine? How many valence electrons are in an atom of magnesium? How many valence electrons are in an atom of phosphorus? How many valence electrons are in an atom of bromine? How many valence electrons are in carbon? By satisfying the duet rule or the octet rule, ions are more stable. An anion is indicated by a negative superscript charge - something to the right of the atom.
Similarly, if a chlorine atom gains an extra electron, it becomes the chloride ion, Cl —. Both ions form because the ion is more stable than the atom due to the octet rule. Once the oppositely charged ions form, they are attracted by their positive and negative charges and form an ionic compound. Ionic bonds are also formed when there is a large electronegativity difference between two atoms.
This difference causes an unequal sharing of electrons such that one atom completely loses one or more electrons and the other atom gains one or more electrons, such as in the creation of an ionic bond between a metal atom sodium and a nonmetal fluorine. Formation of sodium fluoride : The transfer of electrons and subsequent attraction of oppositely charged ions.
To determine the chemical formulas of ionic compounds, the following two conditions must be satisfied:. This is because Mg has two valence electrons and it would like to get rid of those two ions to obey the octet rule. Fluorine has seven valence electrons and usually forms the F — ion because it gains one electron to satisfy the octet rule.
Therefore, the formula of the compound is MgF 2. The subscript two indicates that there are two fluorines that are ionically bonded to magnesium. On the macroscopic scale, ionic compounds form crystalline lattice structures that are characterized by high melting and boiling points and good electrical conductivity when melted or solubilized. Fluorine has seven valence electrons and as such, usually forms the F — ion because it gains one electron to satisfy the octet rule.
Covalent bonds are a class of chemical bonds where valence electrons are shared between two atoms, typically two nonmetals. The formation of a covalent bond allows the nonmetals to obey the octet rule and thus become more stable. For example:. Covalent bonding requires a specific orientation between atoms in order to achieve the overlap between bonding orbitals.
Sigma bonds are the strongest type of covalent interaction and are formed via the overlap of atomic orbitals along the orbital axis. The overlapped orbitals allow the shared electrons to move freely between atoms. Pi bonds are a weaker type of covalent interactions and result from the overlap of two lobes of the interacting atomic orbitals above and below the orbital axis.
Unlike an ionic bond, a covalent bond is stronger between two atoms with similar electronegativity.
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