Last updated on
January 5, 20226 min readYear 10, Science
Definitions
Ion: An atom which is electrostatically charged
Cation: Positively Charged ion
Anion: Negatively Charged ion
Valence shell: Outermost electron shell
Octet: 8 electrons in the valence shell (2 if the element is Hydrogen or Helium)
Catalyst: something that causes and/or speeds up chemical reactions
Proton: positively charged hadron
Neutron: neutral hadron
Electron: negatively charged lepton
exothermic: emits heat
endothermic: absorbs heat
Atomic number: number of protons
Atomic mass: number of protons + number of neutrons
Neutralisation: mixing an acid and a base to create water
Corrosion: a gas or liquid chemically attacking an exposed surface
Combustion: exothermic reaction between a fuel and oxidiser, which produces heat, light and gaseous products
decomposition: when a single compound breaks down into two or more compounds
oxidisation: corrosion reaction where the gas/liquid is Oxygen (O)
Precipitation: formation of an insoluble solid when two soluble solutions are combined (product is known as a precipitate)
Acid-Metal reaction: when an acid and metal react to produce a metallic salt and Hydrogen
Periodic Table
The periodic table is a table listing the fundamental building blocks of the universe: elements
NOTE: ATOM and ELEMENT do NOT mean the same thing!
An atom is a particle containing protons and electrons (and generally neutrons too)
An element is a substance made out of the SAME TYPE OF ATOM
An atom is the smallest sample of an element.
Atoms have a nucleus (which contains their protons and neutrons) and orbiting shells (which contain electrons in fixed rings)
Electron shells fill from the innermost available space:
The first shell can hold a MAXIMUM of 2 electrons
The second shell can hold a maximum of 8 electrons
The third shell can hold 8 electrons until the fourth shell has 2 electrons, then another 10 (total of 18)
This concept is a bit confusing at first. Click here to see how it works
- In the fourth period, Potassium has an electron configuration of Potassium is $ 2,8,8,1 $
- Calcium is $ 2,8,8,2 $
- Scandium is $ 2,8,9,2 $ . After the 4th shell has 2 electrons, they begin to fill from the 3rd shell until Zinc, which fills the third shell to its capacity of 18 ( $ 2,8,18,2 $ ).
- After Zinc, electrons fill the outermost shell again until Krypton ( $ 2,8,18,8 $ ), after which the fifth shell starts filling.
- This trend occurs for shells 3/4 and 4/5.
- The fourth shell can hold 8 electrons until the fifth shell has 2 electrons, then another 10 (total of 18)
Memorising the first 20 elements
There is an easy way to memorise the first 20 elements, the Periodic Table Song
You should memorise up to the first chorus (including the chorus) for Year 10 Chemistry. Year 11 and 12 Chemistry may require more.
Representing Atoms
There are several ways to represent an atom.
The first way is the atom’s symbol.
The atomic symbol is the one or two letter shortcode for the atom that can be seen on the periodic table.
For example, Oxygen is represented as $ O $ , while Calcium is $ Ca $
The first letter MUST be capital and the second letter (if present) MUST be lowercase. $ ca $ , $ CA $ or $ cA $ for Calcium are all INCORRECT answers.
Some elements have atomic symbols which somewhat match their name, such as $ N $ for Nitrogen
Others seem completely random, such as $ Au $ for Gold. These tend to come from their Latin names (“Aurum” in the case of Gold)
Another way is by writing out the ELECTRON CONFIGURATION.
This is the filling order of the electron shells.
For example, Hydrogen is $ 1 $ , Oxygen is $ 2,6 $ , etc.
This method is not often used for naming an element, since electron configurations can change in Chemical Reactions.
Chemical Reactions
A chemical reaction is when the bonds between atoms are broken, formed or changed
A chemical reaction has 2 parts: reactants and products
Reactants are the substances BEFORE the reaction
Products are the substances AFTER the reaction
Law Of Conservation Of Mass
The Law of Conservation of Mass states that:
Matter cannot be created nor destroyed, it can only be changed from one form to another.
- This means that in a chemical reaction, the total mass of the products MUST be the same as the total mass of the reactants.
- For example, photosynthesis:
- 6CO2 + 6H2O —> C6H12O6 + 6O2
- On both sides of the equation, there are:
- 6 Carbon atoms
- 6 Oxygen atoms
- 12 Hydrogen atoms
- This is known as a BALANCED EQUATION
### Law of Constant Proportions
- The Law of Constant Proportions states that:
-
A given chemical compound always contains its components in a fixed ratio.
For example, in water, there will ALWAYS be two hydrogen atoms for every oxygen atom (H2O).
If there were an equal number of hydrogen and oxygen atoms, then the substance would not be Water (H2O), instead it would be Hydrogen Peroxide (H2O2).
Exothermic and Endothermic Reactions
An EXOTHERMIC REACTION is a reaction that GENERATES heat/energy (exo-: outside, -thermic: heat)
An ENDOTHERMIC REACTION is a reaction that REQUIRES heat/energy (endo-: inside, -thermic: heat)
Sometimes, exothermic reactions require heat to start. However, their total energy output is GREATER than the total energy input
Ionic and Covalent Bonds
An IONIC bond is a bond between oppositely charged IONS (atoms with an unequal number of protons and electrons)
Ionic bonds occur between a metal and a non-metal
One atom will LOSE electrons, and the other will GAIN electrons so that both have a filled outer shell.
For example, in $ NaCl $ , The Sodium atom loses an electron and the Chlorine atom gains that electron. The two atoms are then electrostatically attracted together.
A COVALENT bond is a bond where two non-metal atoms SHARE a pair of valence electrons
An atom can have multiple covalent bonds. For example, carbon group atoms can have up to four covalent bonds
Noble Gases (group 18) do NOT form bonds with anything (except in rare circumstances)
Two atoms with a covalent bond can be said to be DIATOMIC
VIDEO TUTORIAL: Lewis-Dot Diagrams (<8 minutes)
Element Groupings
The periodic table has several methods of being divided into categories.
The first method is by PERIOD
Elements in horizontal rows are in the same period.
Each at the end of each period, the next electron shell begins to fill.
The second method is by BLOCK
Each block of the periodic table is determined by the electron orbitals which are filled in that block.
Each block is named after the orbital which gets filled in that block
The s-block is everything in columns 1 and 2, as well as Helium
The d-block is everything from column 3 to 12, except the Lanthanides and Actinides
The p-block is everything from column 13 onwards, except Helium
The f-block is the Lanthanides and Actinides
The third method is by GROUP
Vertical columns of the Periodic Table are known as GROUPS
Elements in the same group have similar properties
