shapes and forces

Question 1

intermolecular forces

Answer 1

attractive (repulsive) forces between molecules

Question 2

intramolecular forces

Answer 2

attractive (repulsive) forces within a molecule

Question 3

Van der Waals forces

Answer 3

weak attractive forces between molecules resulting from the formation of temporary dipoles

Question 4

Dipole-Dipole

Answer 4

Dipole-Dipole forces are forces of attraction between the negative pole of one molecule and the positive pole of another

Question 5

hydrogen bonds

Answer 5

• particular types of dipole-dipole attractions between molecules in which hydrogen atoms are bonded to nitrogen, oxygen or fluorine
• the hydrogen atom carries a partial positive charge and is attracted to the electronegative atom in another molecule. Thus, H acts as a bridge between two electronegative atoms

Question 6

the Law of Conservation of Mass

Answer 6

the total mass of the products of a chemical reaction is the same as the total mass of the reactants

Question 7

the Law of Conservation of Matter

Answer 7

that in any chemical reaction, matter is neither created nor destroyed but merely changes from one form into another

Question 8

types of shapes

Answer 8

linear
v-shaped
trigonal planar
trigonal pyramidal
tetrahedral

Question 9

only bonding pairs around the central atom

Answer 9

electrons in the bonding pairs repel each other and want to be as far apart as possible

Question 10

no. of bonding pairs around central atom - 2

Answer 10

shape of molecule - lienar

example - BeH₂ , BeCl₂

bond angle - 180°

Question 11

no. of bonding pairs around central atom - 3

Answer 11

shape of molecule - trigonal planar

example - BF₃ BCl₃

bond angle - 120°

Question 12

no. of bonding pairs around central atom - 4

Answer 12

shape of molecule - tetrahedral

example - CH₄

bond angle - 109.5°

Question 13

lone pairs and bonding pairs around central atom examples

Answer 13

in hback

Question 14

shapes of molecules

Answer 14

• molecules formed when atoms are joined together by covalent bonds
• arrangement of atoms dictates shape of molecule
• figure out arrangement using Electron Pair Repulsion Theory
• Look at the bonding pairs or lone pairs around central atoms

Question 15

lone pairs and bonding pairs around central atom

Answer 15

• lone pairs of electrons closer to nucleus of atom (nuclear charge sucks them in)
• bc of this they are closer together (create strong negative charge)
• their collective nuclear charge pushes bonding pairs further apart
• decreases the bond angle + distorts shape of molecule

Question 16

polarity

Answer 16

• atoms in covalent bonds share electrons

- we figure it out by looking at electronegativity

Question 17

non-polar

Answer 17

when atoms in a covalent bond share electrons equally, bond is said to be non-polar

Eg. H₂ , N₂ , O₂

Question 18

polar

Answer 18

when electrons are shared unequally, bond is polar

eg. HCl, NH₄

Question 19

electronegativity

Answer 19

• the greater the electronegativity, greater the pull on electrons
• to work it out use electronegativity table
• atom w/ greater pull on electrons becomes slightly negative while other atom in bond becomes slightly positive

Question 20

use of electronegativity

Answer 20

can be used to predict nature of a bond

Question 21

everyday life: polar

Answer 21

water (good solvent for ionic and polar substances)

ethanol (used in alcoholic beverages)

Question 22

everyday life: non-polar

Answer 22

tetrachloroethene (used in dry cleaning)

propanone (also called acetone) (used in nail varnish remover)

Question 23

polar molecule can be non-polar overall if it has these shapes

Answer 23

linear
trigonal planar
tetrahedral

ie shapes with no lone pairs

Question 24

eg of polar molecules that is non-polar overall

Answer 24

BeH₂
BF₃
CH₄

Question 25

molecules that are not symmetrical (has one lone pair) are one of these shapes

Answer 25

trigonal pyramidal | v-shaped

Question 26

eg of non-symmetrical molecules

Answer 26

NH₃ | H₂

Question 27

polar bonds and shapes

Answer 27

some molecules, even tho they have polar bonds, doesn't mean they are polar molecules due to their shapes (shape is symmetrical as there are no lone pairs of electrons) eg. carbon dioxide, chloroform, boron trichloride

Question 28

intermolecular bonding

Answer 28

between molecules eg. between water molecules

Question 29

intramolecular bonding

Answer 29

within the molecule eg. an oxygen atom and a hydrogen atom in a molecule

Question 30

3 types of intermolecular bonding

Answer 30

Van der Waals Dipole-Dipole Hydrogen Bonding

Question 31

intermolecular bonding: Van der Waals forces

Answer 31

- temporary dipoles can be set up in non-polar molecules (eg. H₂, O₂) - weak forces of attractions can be set up between oppositely charged poles in the atom - do not last v long - weakest of 3 types - low boiling points

Question 32

intermolecular bonding: Dipole-DIpole forces

Answer 32

- polar molecules have positive + negative poles eg. HCl - positive pole of one molecule can become attracted to negative pole of another - much weaker than ionic bonds

Question 33

intermolecular bonding: Hydrogen Bonding

Answer 33

- strongest of 3 - N, O, and F are v. electronegative (when bonded with hydrogen, the electron spends more time on the N, O, or F --> creates strong poles) - High boiling points

Question 34

exception to octet rule

Answer 34

BF₃ (boron trifluoride) has trigonal planar shape does not satisfy octet rule (no lone pair present to make 8 in outer shell) as the 3 covalent bonds are stable enough

Question 35

electron pair repulsion theory

Answer 35

The shape of a molecule or ion is governed by the arrangement of the electron pairs around the central atom. to do with repulsion between bond pairs and (if any) lone pairs

Question 36

why h2o has v planar shape

Answer 36

repulsion between two bond pairs and two lone pairs

Question 37

intermolecular vs intramolecular bonds (not definitions)

Answer 37

intramolecular: forces which keeps molecule together, ie. bonds intermolecular: attractive forces between molecules. Responsible for keeping matter in solid or liquid phase

Question 38

bond angles

Answer 38

know the bond angles

Question 39

Predict the type of bond formed between carbon and chlorine atoms in CCl4

Answer 39

polar covalent

Question 40

"why does x have a lower bp than y?"

Answer 40

If electroneg diff is lower in x, then say "smaller degree of intermolecular forces"