Year 9 Revision and recap 1 chemistry

• Definitions

• Atomic structure

• The periodic table

• Electron configuration

• Radioactivity

• Conservation of mass

• Chemical reactions

• Balancing equations

Key definitions

Chemistry uses words that can be confusing or difficult to understand. Key words such as, atom, compound, element, ion, mixture, molecule are used throughout.

Atomic structure

The atomic structure of an atom is made up of 3 subatomic particles:
- Electrons
- Protons
- Neutrons

The periodic table provides us with information about the elements.
- Atomic number
- Element symbol
- Element name
- Atomic mass

The electron configuration of an element allows for us to identify how many electrons it has as well as its capabilities of bonding with another element.

The example shows the calcium atom's electron configuration. How many electrons does it have?

There are rules to follow when drawing electron shell diagrams:
- Each orbital has a maximum number of electrons it can hold.


1st orbital - 2
2nd orbital - 8
3rd orbital - 8
4th orbital - 18




- Think of the bus seat rule - each electron from the 2nd shell onwards wants an electron buddy next to them.
- The number of electrons should be the same as the atomic number

• positively charged ion

• Loses electrons

Cation

• A negatively charged ion

• Gains electrons
  

Anion

Radioactivity

Isotopes are members of a family of an element that all have the same number of protons but different numbers of neutrons.

Some elements will have different number of neutrons and therefore, will go via alternative names. For example, Carbon-12, Carbon-13, and Carbon-14

Synthesis

When 2 or more single elements react to form 1 product.

A + B -> AB

Example: 2Mg + O₂ -> 2MgO

Decomposition

When a compound breakdown into 2 or more simpler products.
AB -> A + B
Example: H₂CO₃ -> CO₂ + H₂O

Single replacement

When a single element replaces another element in a compound
A + BC -> AC + B
Example: Zn + CuCl₂ -> ZnCl₂ + Cu

Double replacement

The cations and anions of two compounds switch places
AB + CD -> AC + BD
Example: HCl + NaOH -> NaCl + H₂O

Conservation of mass

The conservation of mass states that mass is neither created nor lost during chemical reactions.

This is important to remember when balancing equations...

Word equations

Word equations are the reactants -> products of a chemical reaction written in word format.

EXAMPLE:
Hydrogen + Oxygen -> Water