Chemistry

• Elements on the left side of the periodic table have low melting points and are non-metals, while those on the right side have high melting points and are metals.
• atoms are the smallest particles of an element

  all atoms are made up of a nucleus with electrons orbiting around it
• an element is a substance that cannot be broken down into simpler substances by chemical reactions
• A compound is a substance made up of two or more elements chemically combined.
• how to balance equations

  
• difference between compounds and mixtures

  
• filtration is used to separate insoluble solids from liquids
• distillation is used to separate a solvent from a solute
• protons have a charge of +1

  electrons have a charge of -1

  neutrons have a charge of 0
• number of neutrons = mass number - atomic number

  
• an ion is a charged atom or molecule that has gained or lost electrons making the ion either positive or negative
• atoms of the same element with different numbers of neutrons are called isotopes

  isotopes always have the same atomic number but different mass numbers
• sometimes extra neutrons make the nucleus unstable, making it radioactive but not all isotopes are radioactive
• isotopes of an element have different physical properties (e.g. their density or if they are or aren't radioactive)

  as their atoms will have the same number of protons and electrons, the structure will be the same for all isotopes of an element
• electron shell diagram: shows the arrangement of electrons in the outermost shell of an atom

  
• info

  
• What are the intermolecular forces like in simple molecular substances?

  They are weak and easily broken
• What are giant covalent structures?

  Large structures made of billions or trillions of atoms
• Why are giant covalent structures strong?

  All atoms are joined by covalent bonds
• What is the result of transferring electrons in ionic bonding?

  It creates oppositely charged ions that attract each other
• What is a dot and cross diagram used for?

  To represent covalent bonds and show which electrons belong to each atom
• What happens when two non-metal elements, like chlorine atoms, interact?

  They share electrons instead of transferring them
• How should you differentiate the electrons in a dot and cross diagram?

  By using dots for one atom and crosses for the other
• What is a displayed formula?

  A representation using chemical symbols and lines to show covalent bonds
• Octet Rule

  Atoms tend to gain, lose, or share electrons to achieve 8 valence electrons.
• What are the strengths and weaknesses of different representations of covalent bonds?

  Strengths:

  • Dot and cross diagrams show electron sharing
  • Displayed formulas simplify complex structures
  • 3D models show actual arrangement of atoms

  
  

  Weaknesses:

  • Dot and cross diagrams can be complex for large molecules
  • Displayed formulas do not show 3D shape
  • 3D models can be difficult to interpret
• How do atoms form ionic bonds?

  By transferring electrons from one atom to another
• What are the different ways to represent covalent bonds?

  • Dot and cross diagrams
  • Displayed formulas
  • 3D models