Unit 1 - Chemical Changes and Structure (Structure and Bonding) Flashcards
What is an intramolecular bond?
A bond within molecules
What are the three types of intramolecular bond?
- Pure covalent bonds
- Polar covalent bonds
- Ionic bonds
What is a pure covalent bond?
- A covalent bond (a shared pair of electrons, electrostatically attracted to the positive nuclei of two atoms) between two atoms of the same electronegativity value.
- Has no ionic character at all (electrons are shared equally, without being uneven).
- Diatomic elements are good examples of pure covalent bonds where the electrons are evenly shared between both nuclei.
What is a polar covalent bond?
- Where one of the atoms involved in the covalent bond will be more electronegative (has a greater attraction for the bonding pair of electrons) than the other atom.
- The shared pair of electrons is not shared equally between the two atoms.
- The atom with the higher electronegativity will pull the bonding electrons towards itself, creating a slightly negative charge known as a dipole.
What is an ionic bond?
- Usually arises between metal and non-metal atoms with a large difference in electronegativity.
- The atom with the larger electronegativity will pull the bonding electrons towards itself, gaining an electron and forming a negative ion.
- The atom with the smaller electronegativity will lose its bonding electron to the atom with the larger electronegativity, forming a positive ion.
- Atoms gain or lose electrons for mutual benefit.
- Allows atoms to gain a full outer shell of electrons and become stable.
- The electrostatic force of attraction between a metal ion and a non-metal ion.
- Ions are arranged into a three-dimensional ionic lattice of positive and negative ions.
- Have high melting points and boiling points, are solid at room temperature, and only conduct electricity when in solution/molten (ions are free to move around).
- Can be broken down through electrolysis.
What is bonding continuum?
A scale of differences between electronegativity which determines the type of bond that will arise between molecules.
- Pure covalent bond: zero difference in electronegativity.
- Polar covalent bond: low difference in electronegativity.
- Ionic bond: high difference in electronegativity.
What is an intermolecular force/Van der Waals force?
A bond that arises between molecules and is weaker than an intramolecular bond.
What are the three types of intermolecular force?
- London dispersion forces.
- Permanent dipole-permanent dipole interactions.
- Hydrogen bonding.
What are London dispersion forces?
- The weakest type of intermolecular bond.
- Exist between all atoms and molecules (as they all have electrons).
- Where the electrostatic attraction between temporary dipoles and induced dipoles form between the slightly positive end of one atom/molecule and the slightly negative end of one atom/molecule due to the movement of electrons in atoms and molecules.
- Caused by an uneven distribution of electrons within an atom. This results in a slightly negative and slightly positive
charge on either side of the atom. A temporary dipole has been established. This temporary dipole can induce a temporary dipole on a neighbouring atom/molecule. - The strength of the London dispersion forces is dependent on the number of electrons within an atom or molecule.
- Non-polar molecules only contain London dispersion forces.
What are permanent dipole-permanent dipole interactions?
- Arises between polar molecules (asymmetric molecules) alongside LDFs.
- Polar molecules display attractions between the oppositely charged ends of the molecules.
- Stronger than London dispersion forces with the same number of electrons.
What is hydrogen bonding?
- A type of Pd-Pdi interaction.
- The strongest out of the three Van der Waals forces.
- The electrostatic forces of attraction between molecules that contain highly polar bonds, such as O-H, N-H, H-F.
- Formed between atoms of a large difference in electronegativity.
- Occurs when a hydrogen atom is covalently bonded to a highly electronegative element such as nitrogen, oxygen or fluorine.
- The oppositely charged ends of molecules attract.
What is the relative strengths of the different types of bonds?
Covalent bonds > Hydrogen bonds > Permanent dipole interactions > London dispersion forces.
What is a polar molecule?
An asymmetrical (bent) molecule which as a negative and positive side.
What is a non-polar molecule?
A symmetrical (linear) structure which does not have a positive or negative side.
What does having more hydroxyl groups enable a molecule to do?
- Dissolve in polar substances such as water.
- Has more hydrogen bonds.
- Is more viscous.
- Has a higher melting point and boiling point.
