Level 2 Structure and Bonding

What are the 4 types of solids?

Ionic, Metallic, Covalent Molecular, Giant Covalent Network

What are ionic solids composed of?

Metal and a non-metal ions.

What are metallic substances composed of?

Metal cations and delocalised electrons

What are covalent molecular solids composed of?

Lots of single molecules that are stuck together

What are giant covalent networks composed of?

They are made up of one big molecule/lattice that is held together by covalent bonds

Describe the hardness of ionic solids...

Ionic solids are hard because they have strong ionic lattice bonds between their ions.

Are ionic solids brittle? Why?

Yes, because if a large force is applied to them, their ions would line up in such a way that they would repel each other and the crystal would shatter.

Do ionic solids have high or low melting points and why?

They have high melting points because a lot of heat energy is needed to break the strong ionic bonds between the ions.

What does it mean when something is malleable?

It is able to bend into a new shape and stay in that shape.

What does it mean when something is ductile?

It is able to be stretched out into wire.

Are ionic solids malleable or ductile?

No they are not either because if 2 ions of the same charge went next to each other, the cubic attraction' would shatter because the ions would repel each other.

Can ionic compounds conduct electricity? Why?

No they cannot because their electrons are not free to move but if they are heated or dissolved, they can because their ions would be broken up.

Define Solvent

The liquid that the solid is dissolved in.

Define Solute

The solid that is dissolved in the liquid.

What must happen in order for something to dissolve?

The solvent-solute attraction must be greater than the solvent-solvent attraction and the solute-solute attraction.

Describe the hardness of metallic solids...

Metallic solids are very hard because they have strong metallic bonds between their ions.

Are metallic solids brittle? Why?

No they are not because the bonds between their delocalised electrons are non-directional.

Do metallic solids have high or low melting points and why?

They have very high melting points because a lot of energy is needed to break their strong metallic bonds.

Are metallic solids malleable or ductile?

Metals are both malleable and ductile because since their bonds are constantly moving, they can't be broken so the metal won't shatter when a force is applied.

Can metallic compounds conduct electricity? Why?

Metals can conduct electricity as a solid because their charged particles are free to move. If they are melted, they can also conduct electricity.

Do metals dissolve? Why?

Metals do not dissolve because the solvent-solute attraction isn't strong enough, due to the strong metallic bonding within the solute.

Describe the hardness of molecular solids...

Molecular solids are not very hard because they have weak inter molecular bonds.

They have low melting points because little energy is needed to break their weak inter molecular bonds

Do molecular solids have high or low melting points and why?

Do molecular solids conduct electricity?

They do not conduct electricity because they do not have freely moving charged particles.

What are the 3 covalent networks talked about in Level 2?

Diamond, graphite and silicon dioxide

Do covalent networks have high or low melting and boiling points and why?

They have very high melting points because a large amount of energy is required to break the strong covalent bonds.

Do covalent networks conduct electricity?

They do not conduct electricity (except graphite because the 4th electron from each carbon atom is delocalised).

What are the 3 types of bonding?

Ionic, metallic and covalent.

What is ionic bonding?

Ionic bonding is the electrostatic attraction between positive and negative ions.

What is metallic bonding?

Metallic bonding is when positive metal ions are held together by delocalised electrons.

What is covalent bonding?

Covalent bonding is when one or more pairs of electrons are shared by two atoms.

In a molecule, how do electrons arrange themselves?

They arrange themselves to be as far away from each other as possible to minimise repulsion.

What does VSEPR stand for?

Valence Shell Electron Pair Repulsion

What is the shape name and bond angle of a molecule that has 2 regions of electron density?

Linear - 180 degrees

What is the shape name and bond angle of a molecule that has 3 regions of electron density?

Trigonal Planar - 120 degrees

What is the shape name and bond angle of a molecule that has 4 regions of electron density?

Tetrahedral - 109.5 degrees

What is electronegativity?

Electronegativity is a measure of the ability of an atom in a molecule to attract electrons in a chemical bond to itself.

What makes a molecule polar?

A molecule is polar if it has one end which is more negatively charged and one end which is more positively charged.

How are polar bonds (dipoles) formed?

Polar bonds are formed when two bonded atoms have different electronegativities.

What happens if a molecule's dipoles are arranged symmetrically?

The dipoles will cancel each other out, making the molecule non-polar.

What happens if a molecule's dipoles are arranged asymmetrically

Its dipoles will not cancel each other out, so the molecule will be polar.

Which side of FONClBrISCH is the most electronegative (δ−)?

The left side, starting from F

What do the dipoles in polar molecules do?

They attract each other to form strong inter-molecular bonds.

What does it mean if something has strong inter-molecular bonds?

The stronger the inter-molecular bonds something has, the more energy is required to break those bonds and therefore the higher the melting/boiling point of that molecule.

Why are polar molecules normally soluble in water?

Because they can form inter-molecular bonds with the water molecules.

What is enthalpy (H)?

Enthalpy is a measure of the energy within the reactants or products of a reaction.

What is enthalpy change (ΔH)?

Enthalpy change is the heat change that takes place during a reaction.

What is the equation for enthalpy change?

ΔH = Hproducts - Hreactants

(Enthalpy change = enthalpy of products - enthalpy of reactants)

What is the unit for enthalpy change?

kJ/mol-1

What happens in an exothermic reaction?

1) Heat energy is given out to surroundings (temperature rises).

2) Enthalpy change is negative

What happens in an endothermic reaction?

1) Heat energy is taken in from the surroundings (temperature drops).

2) Enthalpy change is positive

What happens in bond breaking?

Bond breaking requires energy to be taken in by the molecule. It is an endothermic process.

What happens in bond making?

Bond making releases energy to the surroundings. It is an exothermic process.

What happens during a reaction, in regards to bond breaking and bond making?

During a reaction, reactant bonds are broken and product bonds are made.

What determines whether a reaction will be exothermic or endothermic overall?

The difference in energies of the bond breaking and bond making processes.

How do you calculate the total energy change (ΔH) of a reaction?

1) Calculate the energy needed to break all of the reactant bonds ∑H(reactants).

2) Calculate the energy released when all of the product bonds are formed ∑H(products).

3) ΔH = ∑H(reactants) - ∑H(products)

Positive answer = endothermic reaction

Negative answer = exothermic reaction

What is enthalpy change of a reaction (ΔrH)?

Enthalpy change of a reaction is the enthalpy change for a given chemical reaction.

How can we predict the enthalpy change of a reaction?

1) Calculate moles of the given substance.

2) Use the mole ratio and (ΔrH) to calculate the enthalpy change for 1 mole of the given substance.

3) Multiply answers from part 1 and 2 to determine the enthalpy change.

Tetrahedral

4 areas of electron density - 4 bonded

triogonal pyramidal

4 areas of electron density - 3 bonded 1 non

bent

4 areas of electron density - 2 bonded 2 non bonded

triogonal planar

3 areas of electron density - 3 bonded

linear

2 areas of electron density - 2 bonded