Chemistry (Term 2)

Order (small to large):

1. Atoms

2. Molecules

3. Elements

4. Compounds / Mixtures / Alloys / Composites

Atoms

Definition:

• An atom is the smallest particle of a chemical element that can exist

Electronic structure:

• Draw the electrons based on electronic configuration (2.8.8.2)

• The outermost shell is known as the valence shell

Constituents:

• Protons (+1)

• Neutrons (0)

• Electrons (-1): Relative mass of 1/1837

Valency

• Noble gases are unreactive due to their full valence shell

• This electronic structure is very stable

• If the valence shell is not full, the element is unstable, reactive and volatile

• Valency is the ability to bond with other atoms based on how many electrons it needs to gain or lose to fill the valence shell

Elements

Definition:

• An element is made up of many different atoms

Nucleon number: Protons + Neutrons

Protons = Neutrons (Electrically neutral)

Chemical formula (Symbol)

Nuclide notation - the whole group

Periodic table:

• Group - top to bottom

• Period - Left to right, metals to non-metals

Compounds

Definition:

• A pure substance made up of 2 or more elements which are chemically combined together in a fixed ratio. They have different chemical and physical properties as their constituent elements.

• Methods of separation such as magnets, electrolysis and filtration have to be used

• Example: Iron sulfide (From iron and sulfur)

Alloys

Example: Stainless steel (From iron, chromium, nickel and carbon)

Definition:

• A metal made by combining 2 or more metallic elements, creating a stronger metal

• Atoms of different sizes distort the regular arrangements of atoms, making it more difficult for the layers to slide over each other, so alloys and stronger and harder than pure metal.

• It is a mixture (same type/category)

• The elements are not chemically bonded and can have various ratios

Mixtures

Definition:

• A mixture of 2 or more elements which are not chemically combined together

• They can be mixed in any proportion or no proportion

• Use decanting or filter paper to separate

• Example: Sea water, fizzy drinks

Composites

Definition:

• Composite materials are formed by combining more than one material to obtain the desired properties.

• 1 material (matrix) surrounds the other material

Isotopes

Definition:

• Isotopes are atoms of the same element with the same number of protons but different number of neutrons (nucleon number)

• As they have different neutrons, their masses and construction would be different. Thus, this affects physical properties such as density and melting point

Ions

Definition:

• An ion is an atom or molecule with a net electric charge due to the loss or gain of one or more electrons

• Metal elements are positively charged (cations) and have “extra electrons” (+), while non-metallic elements are negatively charged (anions) and have “little electrons” (-)

• Non-Metal ions end with “-ide”

  

Molecules

Definition:

• A molecule is made up of one or more atoms connected by covalent (chemical) bonds

• They are chemically bonded together

Properties of materials

• Melting Point

• Boiling Point

• Density (Mass per unit volume)

• Strength (Support heavy load without tearing or breaking)

• Hardness (Withstand wear and scratches; Measured with a Mohs’ scale)

• Flexibility (Bend without breaking)

• Malleability (Hammered into different shapes without breaking)

• Ductility (Pulled or stretched into wires)

• Electrical Conductivity

• Thermal Conductivity

Metals and other materials corrode, iron rusts

Summary

Solution vs Suspension