12CHX 2.4 Structure and Bonding

Compare and contrast the shapes of two molecules

1. BOTH molecules have _ 2. Electron density around central atom 3. These areas repel 4. The parent arrangement is _ with a bond angle of _ 5. Bonding regions and lone pairs 6. Therefore its shape is 7. However, (repeat for other molecule)

"Justify the polarity of each molecule"

"1. Both _ and _ have a shape of _ which is (a)symmetrical 2. Polar bonds due to EN difference between x and y, creating bond dipoles 3. Same/different size dipoles & (a)symmetrical arrangement 4. They do/don't cancel out so _ is (non)polar 5. However, (repeat for other molecule)"

"Why is one substance ( ) while another is not"

"1. Explain structure and bonding of both 2. General statement of requirement for property 3. Link molecules to the statement and (dis)qualify"

What is a polar bond?

A covalent bond with a dipole

What is the general statement for electrical conductivity

For a substance to conduct electricity, it must have free to move charged particles

"How do you explain an ionic substance conducting electricity"

"Ionic substances cannot conduct in the solid phase because the ions are held in a rigid 3D lattice and cannot move. In a molten liquid state, the lattice is broken down and the ions are free to move to carry the charge."

"What is the general statement for malleability/ductility"

"For a substance to be malleable/ductile it must have non-directional bonds (only metallic solids). For metals, you should say that the layers of cations are able to slide over themselves and form new metallic bonds without breaking the structure."

What is the general statement for melting point

A substance's melting point is determined by the strength of the attractive forces between particles and how much energy is required to break the force of attraction between particles

What is the general statement for hardness

A substance's hardness is determined by the strength of the bonds and how much force is required to overcome them.

Explain the structure and bonding of metallic solids in one sentence

Metallic solids are made up of metal cations surrounded by a sea of delocalised electrons, held together by strong non-directional metallic bonds created by the electrostatic attraction between the metal cations and the valence electrons.

Metallic solids are made up of metal ____ surrounded by a sea of delocalised electrons, held together by strong ____ created by the ____ between the metal cations and the ____.

cations, non-directional metallic bonds, electrostatic attraction, valence electrons

Explain the structure and bonding of molecular substances in one sentence

Molecular substances are made up of discreet molecules held together by weak intermolecular forces

Explain the structure and bonding of ionic solids in one sentence

Ionic solids are made up of alternating cations and anions in a 3D lattice, held together by strong highly directional ionic bonds created by the electrostatic attraction between the cations and the anions

Ionic solids are made up of ____ in a 3D lattice, held together by strong ____ created by the ____ attraction between the ____.

alternating cations and anions, highly directional ionic bonds, electrostatic, cations and anions

What is the general statement for being brittle

For a solid to be brittle, it must have directional bonds.

"Explain the structure and bonding of graphite in one sentence"

"Graphite is an extended 2D covalent network solid made up of carbon atoms held together by strong directional covalent bonds, where each carbon is bonded to 3 others in a trigonal planar arrangement, with one free valence electron per carbon."

Graphite is an ____ solid made up of carbon atoms held together by ____ bonds, where each carbon is bonded to ____ others in a ____ arrangement, with ____ per carbon.

extended 2D covalent network, strong directional covalent, 3, trigonal planar, one free valence electron

Explain the structure and bonding of diamond in one sentence

Diamond is an extended 3D covalent network solid that is made up of carbon atoms held together by strong covalent bonds, where each carbon is bonded to 4 others in a tetrahedral arrangement

Diamond is an ____ network solid that is made up of ____ held together by ____, where each carbon is bonded to ____ others in a ____ arrangement

extended 3D covalent, carbon atoms, strong covalent bonds, 4, tetrahedral

Explain the structure and bonding of silicon dioxide in one sentence

Silicon dioxide is an extended 3D covalent network solid made up of silicon and oxygen atoms held together by strong directional covalent bonds in a tetrahedral arrangement

Silicon dioxide is an ____ solid that is made up of ____ held together by ____ bonds in a ____ arrangement

extended 3d covalent network, silicon and oxygen atoms, strong directional covalent, tetrahedral

"Why is one substance soluble and another is not"

"1. Briefly explain structure and bonding of each substance (e.g. H2O is a molecular substance held together by weak IMF) 2. State the polarity of each substance 3. Give general requirement for solubility (polar-polar/ionic, non-non) 4. Discuss whether the attractive forces of solute-solvent are great enough to overcome the solu-solu and solv-solv 5. State whether the substance will dissolve"

"How do you explain a polar so dissolving in a polar solvent"

"The S+ H of H2O is attracted to the S- N of NH3 and the S+ H of NH3 is attracted to the S- O of H2O. These new attractions are stronger than the original attractions between NH3-NH3 and H2O-H2O."

"How do you explain a non-polar solute dissolving in a non-polar solvent"

"The I2-C6H12 attractive forces are stronger than the I2-I2 and C6H12-C6H12 forces, so the original forces will be overcome."

"How do you explain an ionic solute dissolving in a polar solvent"

"The S+ H of H2O is attracted to the Cl- ions of NaCl and the S- O of H2O is attracted to the Na+ ions of NaCl. These new attractions are stronger than the original Na-Cl and H2O-H2O. As a result, the ions are pulled out of the lattice and are surrounded by water molecules."

define enthalpy (delta H)

The heat energy absorbed or released by a system during a process, occurring at a constant pressure

"endothermic (bonds, energy, temperature, delta H)"

"break bonds, absorb energy, surroundings cool down, H positive"

"exothermic (bonds, energy, temperature, delta H)"

"make bonds, release energy, surroundings heat up, H negative"

"general paragraph on enthalpy"

"state endo/exo break or form bonds absorb or release energy link to state change if given diagram, more or less CPE"

"enthalpy calcs (bonds sf units)"

"deltaH = BB - BF, 3sf, kJmol-1"

"enthalpy calc (using moles)"

"delta H = Q/n where Q is heat energy in kJ, n is moles in mol (includes n=m/M - mass over molar mass)"