Covalent Bonds
What are covalent bonds?
Covalent Bonds A covalent bond is formed when neutral atoms share one or more pairs of electrons.
Covalent Bonds Covalent bonds form between two or more non-metal atoms (Groups 14-17). Covalent bonded atoms form individual molecules. Covalent compounds can be weak solids, liquids, or gases.
Molecular Compounds A molecule is a neutral group of atoms that are held together by covalent bonds. A chemical compound whose simplest units are molecules is called a molecular compound. Elements in a molecular compound can form multiple substances depending on the numbers of each element. CH methane C H acetylene 4 2 2
How are bond length & bond energy related?
Formation of a Covalent Bond The distance between two bonded atoms at their minimum potential energy is the bond length. Bond energy is the energy required to break a chemical bond and form neutral isolated atoms. Bonds that have the higher bond energies (stronger bonds) have the shorter bond lengths.
How does the octet rule apply to covalent bonds?
Formation of a Covalent Bond Octet Rule Bond formation follows the octet rule: Covalent compounds share electrons so that each atom has an octet of electrons (8) in its highest energy level.
Exceptions to the Octet Rule Hydrogen forms bonds in which it is surrounded by only two electrons. Boron has just three valence electrons, so it tends to form bonds in which it is surrounded by six electrons.
What are the 3 types of covalent bonds?
Single Covalent Bonds When atoms share one pair of electrons, each atom contributes one electron to the bond. Called a single covalent bond, each atom gains the use of one electron for each single bond.
Double Covalent Bonds In a double covalent bond atoms share two pairs of electrons, each atom contributes two and gains two electrons in the bond. In a triple covalent bond atoms share three pairs of electrons, each atom contributes three and gains three electrons in the bond.
How are molecules modeled?
Lewis Structures Electron-dot notation can also be used to represent the structure of molecules, called Lewis Structures. The pair of dots between the two symbols represents the shared electron pair of the hydrogen-hydrogen covalent bond. H H
Lewis Structures The pair of dots between the two symbols represents the shared pair of a covalent bond. In addition, each fluorine atom is surrounded by three pairs of electrons that are not shared in bonds. An unshared pair, also called a lone pair, is a pair of electrons that is not involved in bonding and that belongs exclusively to one atom.
What are the steps for drawing Lewis Structures?
Drawing Lewis Structures Step 1 Get a covalent formula and draw the electron-dot notation for each atom in the formula. H 2 O H H O
Drawing Lewis Structures Step 2 From the electron-dot notation determine how many bonds each atom needs to get an octet. H 2 O
Drawing Lewis Structures Step 3 Determine the central atom (Skip this step if there are only 2 atoms): Carbon is always the central atom If there is more than 1 carbon they make a chain in the center. -C-C-C- Hydrogen & group 17 elements are never in the center. The least electronegative is in the center.
Drawing Lewis Structures Step 4 Spread the remaining elements around the central atom & bond each to the center with a single bond. H 2 O H-O-H
Drawing Lewis Structures Step 5 Compare the number of bonds that each element has with the number of bonds each element needed. Add double or triple bonds as needed. H 2 O H-O-H
Drawing Lewis Structures Step 6 Add unshared electrons to any elements from groups 15, 16 or 17. Valence electrons - bonds made = unshared electrons H 2 O H-O-H
How do covalent compounds share electrons?
Polar & Nonpolar Covalent Bonds Bonds in which atoms share electrons equally are called nonpolar covalent bonds. Electronegativity difference between the two atoms is below 0.3
Polar & Nonpolar Covalent Bonds A polar covalent bond is a covalent bond between atoms in which the electrons are shared unequally. The more electronegative atom attracts electrons more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge.
Polar & Nonpolar Covalent Bonds Electronegativity difference between the two elements is below 2.0 to 0.3. The electron is held closer to the more electronegative atom in the molecule.
Identifying Bond Type Which type of bond (nonpolar covalent, polar covalent or ionic) will form between each of the following pairs of atoms? a. N and H b. F and F c. Ca and Cl d. Al and Cl
How is polarity indicated on Lewis Structures?
Polar & Nonpolar Covalent Bonds The symbol is used to mean partial charge. + is used to show a partial positive charge is used to show a partial negative charge
Polar & Nonpolar Covalent Bonds The O H bonds in a water molecule are polar. The highly electronegative oxygen partially pulls the electrons away from hydrogen.
How are covalent compounds named?
Naming Diatomic Molecular Compounds Diatomic molecular compounds: contain two covalently bonded atoms of the same element The Diatomic 7: H 2 N 2 O 2 F 2 Cl 2 Br 2 I 2 The molecule name is the same as the name of the element. The diatomic 7 do not exist as single atoms in nature. They are always in the diatomic form unless they are in a compound with other elements.
Naming Binary Molecular Compounds Binary molecular compounds: contain two different covalently bonded elements Rule 1. The center element s name is written first. If there is no central atom write the name of the less electronegative element first. Rule 2. The second element in the name: add the suffix -ide to the name of the element. Rule 3. Add prefixes to indicate the number of atoms of each element in the chemical formula. Exception: the prefix "mono-" is only used on the first word for oxygen.
Prefixes for Naming Covalent Compounds
What are the properties of covalent compounds?
Properties of Molecular Compounds They melt and evaporate at low temperatures, many are liquid or gas at room temperature. Solids are weak and can be broken or ground into a powder easily. Not electrical conductors in the solid or liquid state. Often have an odor because of low boiling point
Melting and Boiling Points of Compounds
Properties of Substances with Metallic, Ionic, and Covalent Bonds
Intermolecular Forces What are intermolecular forces? Intermolecular forces are weak forces of attraction between some covalent molecules. These attractions are responsible for determining whether a molecular compound is a gas, a liquid or a solid at room temperature.
Intermolecular Forces How do the strengths of intermolecular attractions compare to intramolecular forces: ionic and covalent bonds? Intermolecular attractions are weaker than either ionic or covalent bonds.
Intermolecular Forces The two weakest attractions between molecules are collectively called van der Waals forces. Van der Waals forces consist of dipole interactions and dispersion forces.
Intermolecular Forces Dispersion forces, the weakest of all intermolecular forces, are caused by the motion of electrons. They occur even between nonpolar molecules. Moving electrons momentarily move to one side of a molecule, their electric force influences the neighboring molecule s electrons to momentarily move to the opposite side.
Intermolecular Forces Dipole interactions occur when polar molecules are attracted to one another. *The electrical attraction occurs between the oppositely charged regions of polar molecules. *Dipole interactions are similar to, but much weaker than, ionic bonds.
Intermolecular Forces Hydrogen bonds are strong attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom.
Intermolecular Forces Hydrogen bond