Chemistry (ECM, atomic structure, chemical bonding)

• define what an element is

  a pure substance that cannot be broken down further into simpler substances
• define what a compound is

  a pure substance that is made up of two or more elements that are chemically bonded
• define what a mixture is

  impure substance that is made up of 2 or more elements/ compounds physically combined together
• compound-melting and boiling point (variable or fixed)

  fixed
• mixture-melting and boiling point (variable or fixed)

  variable
• compound- composition/ ratio (variable or fixed)

  fixed
• mixture- composition/ ratio (variable or fixed)

  variable
• compound- properties compared to its constituents' properties (different or similar)

  different
• mixture- properties compared to its constituents' properties (different or similar)

  similars
• compound- method of separation of its components (physical or chemical)

  chemical
• mixture- method of separation of its components (physical or chemical)

  physical
• ratio- elements

  no ratio
• ratio- compounds

  fixed ratio
• ratio- mixtures

  no fixed ratio
• mpbp- elements

  fixed melting and boiling point
• mpbp- compounds

  fixed melting and boiling point
• mpbp- mixtures

  melting and boiling point varies
• name 3 physical properties of ionic compounds

  1. high melting and boiling points
  2. can conduct electricity
  3. soluble in water
• why do ionic compounds have high mpbp

  1. giant ionic lattice structure
  2. large amount of energy is needed to overcome the strong electrostatic forces of attraction between oppositely charged ions
• why can ionic compound conduct electricity

  1. presence of free-moving ions in molten/ aqueous state allows it to conduct electricity
  2. in solid state, ions are in fixed position hence cannot conduct electricity
• 3 physical properties of covalent compound

  1. low melting and boiling point
  2. cannot conduct electricity
  3. insoluble in water
• why does covalent compound have low mpbp

  1. it has a simple molecular structure
  2. little amount of energy is needed to overcome the weak intermolecular van der waals forced of attraction between molecules
• why cant covalent compound conduct electricity

  1. absence of free moving charged particles
• relative charge of protons

  +1
• relative charge of neutron

  0
• relative charge of electron

  -1
• relative mass of protons

  1
• relative mass of neutron

  1
• relative mass of electron

  1/1840
• what are isotopes

  atoms of the same element with the same number of protons but different number of neutrons
• an element is in group 14. how many valence electrons does the element have

  4
• explain why isotopes have different masses but similar chemical properties

  different masses is caused by different number of neutrons. similar chemical properties is caused by the same number of protons
• what is an ion

  ion is formed when an atom lose or gain electrons
• why do atoms forms ions

  atoms form ions to achieve a noble gas configuration
• what is a cation and how is it formed?

  positively charged ion which is formed by losing electrons to achieve a noble gas configuration
• what is an anion and how is it formed?

  anion is a negatively charged ion which is formed by gaining electrons
• covalent bonds form between non-metals
• the bond formed between atoms sharing electrons is the covalent bond
• covalent substances are made up of simple molecules