Chemistry Paper 1

4.2.1 and 4.2.2

Ionic bonding

A type of chemical bond that occurs when one atom gives an electron to another atom, resulting in the attraction between oppositely charged ions. This type of bonding is when (strong electrostatic forces) occur between positively charged metals and negatively charged nonmetals.

Covalent bonding

A type of chemical bond where atoms share pairs of electrons, resulting in a strong connection between the atoms. This is when an electrostatic attraction between the positive nuclei of two atoms and the negatively charged electrons they share occurs.

Metallic bonding

A type of chemical bond that occurs between metal atoms, characterized by a sea of delocalized electrons that move freely, allowing for electrical conductivity and malleability. This bond involves the electrostatic attraction between positively charged metal ions and these delocalized electrons.

How do the ions produced by elements in some groups have the electronic structure of noble gases?

Elements in certain groups form ions by gaining or losing electrons to achieve a stable, full outer electron shell, like noble gases. The group number indicates the number of electrons an atom has. 

Ionic compounds

Held together by electrostatic forces of attraction between oppositely charged ions and is creates a strong, three-dimensional lattice structure where positive and negative ions alternate.

How to work out the empirical formula of an ionic compound

1. identify the ion and their charges

2. balance the charges

3. write the formula

Types of covalently bonded structures

Small molecules: fixed number of atoms, strong covalent bonds, weak intermolecular forces.

Large molecules: many atoms bonded together, often in long chains called polymers, stronger intermolecular forces.

Giant covalent: substances where a huge number of atoms are held together by strong covalent bonds in a continuous lattice.

How to work out the molecular formula of a substance

Divide the substances known molecular mass by the empirical formula’s mass. Then multiply the result by the subscripts in the empirical formula.

Metallic bonds

A giant structure of positively charged metal ions arranged in a regular lattice, with their outer electrons becoming delocalized and forming a "sea" of electrons that are free to move throughout the structure.

Factors that affect the melting and boiling of a substance

The stronger the intermolecular forces, the longer it take for a substance to melt/boil as more energy is needed to overcome the forces.

What does (s), (l), (g) and (aq) mean?

(s) - solid

(l) - liquid

(g) - gas

(aq) - aqueous (a solution in which a solution is in water)

Structure and affect of ionic compounds

The structure can affect the strength of electrostatic forces and the mobility of the ions.

Structure of small molecules

• low melting and boiling points because atoms are held together by strong covalent bonds and there are weak intermolecular forces between molecules

• not much energy required to break forces between molecules

• usually gases/liquids at room temperature

• the larger the molecules, the stronger the intermolecular forces

• don’t conduct electricity

• (0nly need three points)

Structure of polymers

Longer chains and more crystalline regions generally increase strength and density, whereas extensive cross-linking makes a polymer harder and more difficult to melt.

Structure of giant covalent structures

Large amounts of energy needed to break the numerous, strong covalent bonds, which results in high melting and boiling points and the substance being very hard.

Structure of metals and alloys

In pure metals, atoms are arranged in a regular, layered structure that allows the layers to slide, making them relatively soft and malleable. In alloys, atoms of different sizes disrupt this regular structure, making it difficult for layers to slide and resulting in a harder, stronger material. 

Why are alloys harder than pure metals?

Alloys have different sized atoms which disrupt the regular layers of metal atoms, making it more difficult for the layers to slide past one another.

Properties of graphite, graphene and diamond

Graphite:

• layers of hexagonal rings of carbon atoms (each C atom covalently bonded to 3 others)

• Very soft, good thermal and electrical conductor

• Weak forces between layers

Graphene:

• A 2D layer of carbon atoms arranged in a hexagonal lattice

• Extremely strong, excellent conductor of electricity and heat

Diamond:

• A 3D tetrahedral network in which each C atom is covalently bonded to 4 other C atoms

• Extremely hard, excellent conductor of electricity and heat

Structure of fullerenes (uses, including buckminsterfullerene and carbon nanotubes)

Fullerenes: a hollow, cage-like structures made of carbon atoms arranged in interlocking hexagonal rings, with pentagonal rings required to create the curvature of the cage.

Buckminsterfullerene: (looks like a football) most well-known type of fullerene, has 12 pentagons and 20 hexagons

Nanotubes: a cylindrical structure made of carbon atoms covalently bonded in a hexagonal lattice, similar to a rolled-up sheet of graphene

Nanoparticles

• a lot smaller than other particles (1-100nm)

• large surface area to volume ratio leads to increased reactivity and enhanced catalytic activity(as more particles are exposed and available for chemical reactions and interactions with the environment)

Applications of nanoparticles 

Advantages:

• advanced material strength (sport)

• precise drug delivery within the body

• improved electronic and energy technologies

Disadvantages:

• potential toxicity to human health and the environment

• expensive production

• ethical considerations

• the potential for misuse in weapons