LIST OF TOPICS:

2.1

Chemical bonds

Ionic bonding

Covalent bonding

Metallic bonding

2.2

The three states of matter and their symbols

Properties of ionic compounds

Properties of small molecules

Polymers

Giant covalent structures

Properties of metals and alloys

Metals as conductors

2.3

Structure and bonding of carbon

2.4

Sizes of particles and their properties

Uses of nanoparticles

2.1: Types of Chemical Bonding

Chemical Bonds: 

Chemical bond: two or more elements combine to form compounds

• there are 3 types of chemical bonds

• driven by the need for the atoms to become stable

Ionic bonding:

Ionic bond: the bond between metals and nonmetals of opposite charges (think opposite sides of the periodic table) where electrons are transferred.

• forms an ionic compound

  • held together by attractive forces

  • is a structure of ions, not just a singular ion (ex: cube of NaCl)

• these elements are attracted to each other due to the opposite charges (+ and -)

  • electrons are transferred between elements (these are the valence electrons)

    • metals: lose e- → cation (think cats! they are pawsitive (positive))

    • nonmetals: gain e- → anion

• why does this happen?

  • transferring electrons helps the ions reach a charge of zero, making them neutral and stable (as said above, all chemical bonding is driven by the need for the atoms to become stable!)

• ionic compound will always end in the simplest ratio (empirical formula) to get charges to equal zero

  • ex: Na₂Cl₂ must simplify to NaCl as an ionic compound

Covalent Bonding:

Covalent bond: bond between nonmetals where electron pairs are shared.

• forms a molecule

  • smaller molecules have stronger covalent bonds (the electrons participating in bonding (valence) are closer to the nucleus of the atom; + charge of the nucleus is attracted to - charge of e- more)

  • macromolecules: giant covalent structures, usually bonded through a lattice

• there are polar and nonpolar covalent bonds (depending on the general areas of + or - charge)

Metallic bonding:

Metallic bond: bond between metal cations and delocalized electrons.

• the delocalized electrons form a “sea of electrons” as they move freely throughout the structure

  • also makes metallic bonds strong

2.2: How bonding and structure impact chemical properties

The three states of matter and their symbols:

Solid - (s)

• particles are close together

• vibrate in place

• set volume and shape

Liquid - (l)

• particles have a decent distance between each other

• particles have rotational motion

• set volume, but takes the shape of the container

Gas - (g)

• particles have a lot of distance between each other

• particles move very quickly (lots of motion)

• no set volume (can be compressed → gas pressures) and takes the shape of a container

**Additionally: aqueous - (aq)

• in an aqueous solution, a solute is dissolved in a solvent → homogeneous solution

Phase Changes:

Phase changes you must know: 6 different changes that occur at different points/temperatures

• boiling: liquid to gas (at boiling point)

• condensation: gas to liquid (at boiling point)

• melting: solid to liquid (at melting point)

• freezing: liquid to solid (at freezing point)

• sublimation: solid to gas 

  • ex: dry ice (CO₂)

  • liquid form doesn’t exist at STP but could exist at certain conditions

• deposition: gas to solid

**Melting point/freezing point is the same

**Boiling takes more energy than melting - why?

• melting is s→l, only loosening the bonds

• boiling is l→g, which has to break the bonds

**Breaking bonds absorb energy (endothermic), and forming bonds releases it (exothermic).

Properties of ionic compounds:

Ionic compounds: held together by electrostatic forces of attraction in a lattice structure.

• they can conduct electricity (electrolyte) when melted or dissolved

  • they separate into + or - charged ions

    • the amount of ions = Van’t Hoff Factor

  • have a higher boiling/melting point due to the strong bonds between ions

    • additionally, their Van’t Hoff Factor is greater than in molecules

  • **Covalent molecules do not conduct electricity as they do not break down when melting/dissolving (stay together as one molecule → Van’t Hoff factor of 1)

• Van’t Hoff Factor: # of particles (not quality of particles) that a compound becomes

  • the higher the VHF → the more particles → more interference in bonds between solvent particles → higher boiling/melting point

Properties of small molecules:

Small molecules:

• weak intermolecular forces that break/loosen during phase changes

  • the IMFs break, not the molecule itself!

  • lower boiling/freezing point than larger molecules

• doesn’t conduct electricity (nonelectrolyte)

Polymers:

Polymer: large covalently bonded (strongly bonded) molecule

• usually solid at room temperature due to the strong bonds

• higher boiling and melting points than small molecules

Giant covalent structures:

Giant covalent molecules:

• high boiling and melting points (strong bonds)

• usually solid at room temperature

Properties of metals and alloys:

Metals: giant structure of atoms that are held together through metallic bonding

• high boiling/melting points

• due to the “sea of electrons,” the atoms can slide around, making some metals malleable

Alloys: made of a combination of 2+ different metals

• not as malleable as most regular metals due to the different atom sizes of different elements (harder for them to move around each other)

Metals as conductors:

Metals:

• good conductors of heat and electricity due to the delocalized electrons on the surface

  • they carry and transfer energy

2.3 - Structure and Bonding of Carbon

Structure and bonding of carbon

Diamonds: each carbon is bonded to 4 other carbons

• hard structure, high boiling point, nonelectrolyte (covalent!)

Graphite: each carbon is bonded to 3 other carbons, forming hexagonal layers

• these layers have no covalent bonds between them

  • allows them to slide across each other

  • weak IMFs

  • graphite is slippery and soft

• each carbon atom has a delocalized electron

  • can conduct electricity

Graphene: single layer of graphite

• strong due to the covalent bonds

• slightly flexible without breaking apart bonds

• useful for electronics

Fullerenes: carbon molecule with hollow shapes

• can consist of carbon rings with 5,6, or 7 atoms

• Buckminsterfullerene (C60) - first fullerene discovered (spherical)

• nanotubes: long, cylindrical fullerenes

  • useful for electronics/nanotechnology/etc.

    • reinforce structures (tennis rackets), deliver drugs to the body

2.4 - Bulk and Surface Properties of Matter + Nanoparticles

Sizes of particles and their properties:

Nanoparticles: 1-100 nm (nanometers) across

• include fullerenes

• consist of many atoms

Fine particles: 100-2500 nm

Coarse particles (dust, pollen): 2.5 to 10µm

Microparticles: 1 to 1000µm

Uses of nanoparticles:

• catalysts: high surface area to volume ratio

• lightweight building materials

• selective sensors

• new cosmetics

• lubricant coatings

• electricity

**could be toxic and enter the bloodstream/brain due to small size