Atomic structure t bonding retake

• what is the definition of electronegativity?

  An atom's ability to attract the electron pair in a covalent bond.
• What is the most electronegative element on the periodic table?

  fluorine.
• what makes a bond polar?

  in a covalent bond between 2 atoms of different electronegativities the bonding electrons are pulled towards the more electronegative atom making the bond polar.
• why is a covalent bond between 2 atoms of the same element non-polar?

  because the atoms have equal electronegativities and so the electrons are equally attracted to both nuclei.
• in a polar bond, what creates the permanent dipole?

  the difference in electronegativity.
• what is a dipole?

  a difference in charge between the 2 atoms caused by a shift in electron density in the bond.
• The greater the difference in electronegativity..


  ..the more polar the bond.
• are all molecules containing polar bonds polar?

  no, they are only polar is they contain polar bonds and they are arranged symmetrically in the molecule.
• what happens if the opposite charges aren't symmetrical?

  the charges are evenly spread out and so cancel out.
• what forces are there in a substance made of molecules that have permanent dipoles?

  weak electrostatic forces of attraction between the positive and negative charged on neighbouring molecules.
• what happens if you put a charged rod next to a jet of polar liquid?

  the liquid moves towards the rod, if the rod is negative then the positive side turns to face the rod and moves closer, if the rod is positive then the negative side turns to face the rod and moves closer.
• what are intermolecules forces?

  forces between molecules.
• what are covalent bonds like?

  much weaker than covalent, ionic or metallic bonds.
• how many types of intermolecular bonds are there and what are the names?

  there are 3.

  van der Waals forces/induced dipole-dipole.

  permanent dipole-dipole forces.

  hydrogen bonding.
• why are intermolecular forces important?

  they affect the physical properties of a compound.
• what does van der Waal forces cause?

  all atoms and molecules to be attracted to each other.
• how do Van der Waal forces help atoms and molecules to be attracted to each other?

  electrons in charge clouds ways move fast. The electrons in an atom are likely to be more to one side than the other, at this moment the atom would have a temporary dipole. This dipole can cause another temporary dipole in the opposite direction on a neighbouring atom, the 2 dipole are then attracted to each other. The 2nd dipole can cause another dipole in a 3rd atom. The atoms are constantly moving, dipoles being created and destroyed all the time even though the overall effect is for the atoms to be attracted to each other.
• how do Van der Waal forces hold molecules in a lattice?

  atoms are held together by strong covalent bonds to form molecules. The molecules are then held together in a molecular lattice arrangement by weak Van der Waal forces.
• Stronger Van der Waals forces..


  ..higher boiling points.
• do all Van Der Waal forces have the same strength?

  NO, larger molecules have larger electron clouds so stronger forces.
• aside from strength, what else affects the strength of van der Waals forces? how?

  the shape of molecules. Long straight molecules can lie closer together than branched ones, the closer the molecules get the stronger the forces between them are.
• what happens when you boil a liquid?

  you need to overcome the intermolecular forces so the particles can escape from the liquid surface, You need more energy to overcome stronger intermolecular forces so liquids with stronger van der Waals forces will have higher boiling points.
• alkane chains and van der waals forces

  as the alkane chain gets longer the number of electrons in the molecules increases so the van der Waals forces are stronger and boiling points increases.
• what do van der Waals forces affect?

  melting point and viscosity.
• what is the strongest intermolecular force?

  hydrogen bonding.
• when does hydrogen bonding occur?

  When hydrogen is covalently bonded to fluorine, nitrogen or oxygen.
• how does the hydrogen bonding work?

  fluorine, nitrogen and oxygen are very electronegative so draw bonding electrons away from the hydrogen atom. The bond is very polarised and hydrogen has a high charge density (bc its so small) that the hydrogen atoms form weak bonds with lone pairs of electrons on the fluorine, nitrogen or oxygen atoms of other molecules.
• what do molecules contain that have hydrogen bonding?

  -OH or -NH groups.
• what are 2 molecules that have hydrogen bonding?

  water and ammonia.
• what does hydrogen bonding have an affect on?

  the properties of substances.
• how does hydrogen bonding affect boiling and melting points? eg?

  substances with hydrogen bonding have higher melting and boiling points because of the extra energy needed to break the hydrogen bonds. eg: like with water and hydrogen fluoride (HF has a higher be than other hydrogen halides).
• what is the structure like for ice?


  as liquid water cools to form ice the molecules make more hydrogen bonds and arrange themselves into a regular lattice structure. In this structure, the H20 molecules are further apart on average than the molecules on liquid water so ice is less dense than liquid water.