3.1.3 Bonding Flashcards

Question

What factors affect electronegativity?

Answer 1

- Atomic radius - Nuclear charge - Shielding

Answer 2

Across a period: Electronegativity increases - Number of protons increases = increased nuclear charge. - Atomic radius decreases - electrons in the same shell are pulled in more. - No difference in shielding. Down a group: Electronegativity decreases - Nuclear radius increases. - Shielding increases. - Despite an increase in nuclear charge.

Answer 3

lonic and covalent bonding are 2 extremes of a scale (not 2 separate distinct bonding types) - some molecules may have both ionic and covalent character. Differences in electronegativity between elements can determine where a compound lies on this scale: - A compound containing elements of similar electronegativity & hence a small electronegativity difference (< 0.5) will be purely covalent - A compound containing elements of very different electronegativity & hence a very large electronegativity difference (> 1.7) will be ionic - Compounds with an electronegativity difference between these will either be polar covalent or polar ionic.

Answer 4

A polar covalent bond forms when the elements in the bond have a difference in electronegativities. When a bond is a polar covalent bond it has an unequal distribution of electrons in the bond which causes a slight charge difference, inducing a dipole in the molecule. (The element with the larger electronegativity in a polar compound will be the partially negative end.) Dipole - a permanent or temporary difference in charge between 2 atoms in a covalent bond.

Answer 5

Symmetry of the molecule A symmetric molecule (all bonds identical & no lone pairs) will not be polar even if individual bonds within the molecular are polar. The individual dipoles on the bonds ‘cancel out’ due to the symmetrical shape of the molecule. There is no net dipole moment: the molecule is non-polar.

Answer 6

- Van der Waals' forces - Permanent dipole-dipole forces - Hydrogen bonding

Answer 7

These are also called induced dipole-dipole interactions. They occur between all simple covalent molecules & the separate atoms in noble gases. - In any molecule the electrons are moving constantly and randomly. - As this happens the electron density can fluctuate & parts of the molecule become more or less negative i.e. small temporary dipoles form. - These instantaneous dipoles can cause dipoles to form in neighbouring molecules (induced dipoles). The induced dipole is always the opposite sign to the original one. - A temporary dipole forms between the partially +ive charge in one molecule and the partially -ive charge in a neighbouring molecule.

Answer 8

- The amount of electrons - the more electrons there are in the molecule the higher the chance that temporary dipoles will form. This makes the Van der Waals stronger between the molecules. (The increasing boiling points of the halogens down the group 7 series can be explained by the increasing number of electrons in the bigger molecules causing an increase in the size of the Van der Waals between the molecules. This is why l2 is a solid whereas Cl2 is a gas.) (The increasing boiling points of the alkane homologous series can be explained by the increasing number of electrons in the bigger molecules causing an increase in the size of the Van der Waals between molecules.) - The shape of the molecule - long chain alkanes have a larger surface area of contact between molecules for Van der Waals to form than compared to spherical shaped branched alkanes & so have stronger Van der Waals.

Answer 9

- Occur between polar molecules. - Stronger than Van der Waals & so the compounds have higher boiling points. - Polar molecules have a permanent dipole. - Polar molecules are asymmetrical & have a bond where there is a significant difference in electronegativity between the atoms. Occurs in addition to vdw.

Answer 10

- Occurs in compounds that have a hydrogen atom attached to one of the 3 most electronegative atoms of nitrogen, oxygen and fluorine, which must have an available lone pair of electrons (e.g. a -O-H -N-H F-H bond). - There is a large electronegativity difference between the H & the O, N, F. - Strongest IMF. Occurs in addition to vdw.