Science: Chemistry Year 10

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.
      Image of 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
      Image of the periodic table grouped by 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
      • Group 1: Alkaline Metals
      • Group 2: Alkaline Earth Metals
      • Group 3-12: Transition Metals
      • Group 13: Boron Group
      • Group 14: Carbon Group
      • Group 15: Pnictogens
      • Group 16: Chalcogens
      • Group 17: Halogens
      • Group 18: Noble Gases


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