Unit 4. Covalent Bonding Flashcards
When does covalent bonding occur?
occurs between elements with a difference in electronegativity of fewer than 1.8 units. It occurs between non metal elements
What is a covalent bond
A covalent bond is the electrostatic attraction between positively charged nuclei and shared pairs of bonding electrons.
How are diatomic molecules bonded
Single Covalent bonds for Halogens
Oxygen and nitrogen are also diatomic but the atoms are via double and triple bond.
A double covalent bond consists of four shared electrons, while a triple covalent bond involves the sharing of six bonding electrons.
How does bond length change across single, double and ripple bonds
Consider the group 17 elements, which form diatomic molecules. Atomic radius increases down a group, so the length of the bond between the atoms also increases.
multiple bonds are shorter and stronger than single bonds as they share more electrons between the atoms, so the electrostatic attraction between the bonded nuclei is greater. This greater attraction brings the nuclei closer together
How do covalent bonds weaken?
Longer bonds are weaker than shorter bonds due to the increased distance between the nuclei and the shared pairs of bonding electrons, which results in a weaker electrostatic attraction between the atoms
How do we know of differences in bond lengths in strength
by comparing multiple bonds between atoms of the same element - for example, by comparing the lengths of the carbon-to-carbon bonds in different compounds.
How does bond strengths affect the reactivity of a compound
Bond strength can affect the reactivity of a compound. Nitrogen is unreactive because it has a triple bond, N≡N. It takes a lot of energy to break this bond: 945 kJ mol−1. Oxygen is much more reactive as it only takes 498 kJ of energy to break a mole of O=O bonds.
What is a coordinate covalent bond and give an example
A coordinate covalent bond differs from a ‘regular’ covalent bond because both the bonding electrons come from one atom.
Ex. CO
How do you represent a coordinate covalent bond
With an arrow on the bonds in a Lewis structure. The arrow comes from to atom from which the electrons originate from.
Give an example of a coordinate covalent bond in a polyatomic ionic compound
the hydronium ion (H3O+) and the ammonium ion (NH4+). In the hydronium ion, the coordinate covalent bond is formed between a hydrogen ion and a non-bonding pair of electrons on the oxygen atom. In the ammonium ion, it is formed between a hydrogen ion and the non-bonding pair of electrons on the nitrogen atom.
When do coordinate covalent bonds form? Give an example
Atoms in molecules that are electron-deficient (lacking in electrons) are able to form coordinate covalent bonds. An example of such a molecule is aluminium chloride. Despite being a metal and non-metal atom bonded together, the bonding in aluminium chloride is actually polar covalent, not ionic.
What is a dimer
A dimer is a larger molecule composed of two identical smaller molecules and can be linked by coordinate covalent bonds or by hydrogen bonds.
What is bond order
The bond order is the number of bonds between a pair of atoms. Single bonds have a bond order of 1, double bonds have a bond order of 2, etc.
The higher the bond order, the greater the strength of the bond. Fractional bond orders are possible
How do you calculate bond order
A simple calculation of bond order is to divide the sum of the individual bond orders by the number of bonding groups.
Ex: bond order of CO3 2–.
The carbonate ion is composed of two single bonds and one double bond. The sum of the individual bond orders is 1+1+2 = 4. There are 3 bonding groups in the ion (two single bonds and one double bond), therefore, the bond order is:
4/3 =1.33
What are the two types of covalent bonds
Non-polar and polar
Electronegativity difference for non-polar and polar bonds
Polar covalent= 0.5-1.7
Non polar= 0.1-0.4
What are pure covalent bonds?
Pure covalent bonds occur between atoms that have no difference in electronegativity, such as those found between the diatomic molecules.
What are polar bonds
Polar covalent bonds occur between atoms that have a difference in electronegativity of between 0.5 and 1.7 units.
the bonding electrons are not equally shared between the atoms, creating a bond dipole.
A bond dipole will result in one atom in the bond having a partial positive charge and the other having a partial negative charge.
These partial positive and negative charges are shown by the δ+ and δ- signs respectively.
What is a bond dipole caused by
the unequal sharing of electrons in a covalent bond.
What is the octet rule
The octet rule states that the most stable arrangement for an atom is to have eight electrons in its outermost energy level with the electron configuration of a noble gas.
What are the exceptions to the octet rule
Hydrogen is stable with only two electrons in its outer shell.
Atoms such as boron, beryllium and aluminium (in compounds) are stable with fewer than eight electrons in their outer shell.
Atoms in period three and higher, such as sulfur, can form expanded octets with up to twelve electrons in their valence shell.
What do you call atoms with less than eight electrons in their outer shells
Incomplete octet or electron deficient
What are Lewis structures
Lewis structures (also known as electron dot diagrams) represent the bonding in a molecule; they show both the bonding electrons and the non-bonding electrons (or lone pairs).
What are resonance structures?
When molecules contain multiple bonds (double or triple bonds), there is more than one possible Lewis structure that can be drawn. The different Lewis structures that can be drawn for the same molecule, or polyatomic ion, are called resonance structures.
