Chem Notes M1-3

Question 1

Electronegativity

Answer 1

• “Electron-pulling power of an atom”
• Increases across period, decreases down group
• Determines whether an atomic bond is ionic/covalent

Increases across period, decreases down group because number of positively charged protons increases to the right, making the pull of electrons to the nucelus stronger; and number of electron shells increase going down a group, distancing valence electrons from the nucleus, which weakens the attraction between valence electrons and the nucleus

Question 2

Less than 1.5 difference in electronegativity

Answer 2

• Covalent bond, polar
• Less than 0.4: pure covalent, atoms are of the same element, non-polar

Question 3

More than 1.5 difference in electronegativity

Answer 3

• Ionic bond

Greatest difference between Group 7 and Group 1

Question 4

Intermolecular forces

Answer 4

• Force of attraction between molecules
• 1-50kJ/mol
• Determines physical properties e.g. boiling point (point at which intermolecular attraction breaks, so molecules go from staying together as liquid to gaseous form)
• Types: dispersion, dipole-dipole, hydrogen bonding

Question 5

Dispersion force

Answer 5

• Temporarily uneven distribution of electrons around a molecule creates a temporary dipole, causing weak but very temporary attraction between molecules
• Occurs between any covalent molecules regardless of their polarity, due to constant movement of electrons
• E.g. nitrogen gas and oxygen gas electrons are attracted to both their nuclei and the protons in the nucleus of the other atom.
• Stronger between long, skinny molecules than short, fat ones due to more surface area coming into contact

Intermolecular

Question 6

Dipole-dipole interaction

Answer 6

• Occurs between polar molecules, as they have permanent dipoles
• Stronger than dispersion force because polar covalent dipoles are permanent
• E.g. HCl, H2S

Intermolecular

Question 7

Hydrogen bonding

Answer 7

• Type of dipole-dipole force
• Only occurs between H and F, O, or N because F, O, N and H have very large differences in electronegativity
• 1/10th strength of an intramolecular covalent bond, strongest of all intermolecularforces
• E.g. methanol (CH3OH), H2O

Intermolecular

Question 8

Intramolecular force

Answer 8

• Attraction between atoms in a single molecule
• 150-1100 kJ/mol strength - stronger than intermolecular bonds
• Takes more energy to break
• Types are ionic, covalent, and metallic bonding

Question 9

VSEPR

Answer 9

• Valence Shell Electron Repulsion Theory
• Electron pairs in a molecule repel each other because they are all negative → spread out evenly around the atoms
• Lone pairs have stronger repulsion than bond pairs → pushes other bond pairs down

Question 10

Synthesis reaction

A.K.A Combination reaction

Answer 10

• 2 or more reactants combine to form an aggregate product
• A + B → AB

Question 11

Decomposition reaction

Answer 11

• A reactant breaks down into multiple products
• AB → A + B

Question 12

Combustion reaction

Answer 12

• Exothermic reaction between fuel and oxidant to produce CO2, H2O, and energy.

• Incomplete combustion produces CO2, H2O, energy, CO, and soot (solid carbon)

Question 13

Precipitation reaction

Answer 13

• 2 soluble reactants react to form an insoluble solid (precipitate)
• AB (aq) + CD (aq) → AD (aq) + CB (s)

Question 14

Acid/base reaction (neutralisation)

Answer 14

• Acid + base → salt + water

Question 15

Acid/carbonate reaction

Answer 15

• Acid + base → salt + carbon dioxide + water

Question 16

Mole

Answer 16

• 6.022x10^23
• Abbreviated “mol” or “n”
• Also known as Avogadro’s Number