atoms,elements and compounds

• define an element?


  a substance made up of one type of atom
• define a compound?

  two or more elements that are chemically combined
• define a mixture?

  two or more elements that are not chemically combined
• define (mass)nucleon number?

  the combined number of neutrons and protons in the nucleus
• define (atomic)proton number?

  the number of protons in the nucleus
• whats an ion?


  a charged atom formed by atoms losing or gaining electrons
• whats a molecule?


  two or more atoms bonded together
• define the term isotope?


  atoms of the same element with the same number of protons but different number of neutrons
• whats the formulae of relative atomic mass?

  (mass number*abundance)+(mass number*abundance)

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  100
• why do isotopes have the same chemical properties?

  Same number of electrons.

  same number of electrons in outer shell.
• cation?

  a positive ion
• anion?

  a negative ion
• define ionic bond?

  strong electrostatic attraction between oppositely charged ions
• ionic compound properties?


  good electricity conductors when molten or in aqueous solution and poor when solid.

  high melting and boiling points.
• describe a giant ionic lattice?

  regular arrangement of alternating positive and negative ions.
• describe in terms of forces of attraction why ionic compounds have high melting and boiling points?

  strong electrostatic attraction between ions
• explain in terms of structure why ionic compounds cant conduct electricity when solid?


  strong forces between ions prevent them from moving
• explain in terms of structure why ionic compounds conduct electricity when molten or in aqueous solution?

  strong forces between ions have been broken down so they are free to move
• how does a covalent bond form?

  a pair of electrons is shared between two atoms leading to noble gas configuration
• why do covalent bonds have low melting and boiling points?

  weak intermolecular forces
• why are covalent bonded compounds poor electrical conductors?


  none-electrolytes meaning they don't have ions and so they cannot carry an electrical current.
• describe the giant structure of diamond?

  tetrahedral structure each carbon atom is covalently bonded to four others
• describe the giant covalent structure of graphite?

  each carbon atom is bonded to three others
• explain in terms of bonding why diamond is used in cutting tools?

  extremely strong bonds which make it an extremely hard substance
• why is graphite used as a lubricant and as an electrode?

  lubricant: weak forces of attraction between layers allow them to slide over each other.

  electrode: the fourth unbonded electron from each carbon atom is delocalized and so can move along the layers.
• describe the structure of silicon(IV)oxide?

  each silicon atom has four covalent bonds.
• describe the similarity between diamond and silicon(IV)oxide?

  their similar structures allow them both to have a high melting and boiling point and are hard substances.
• define metallic bonding?

  electrostatic attraction between a positive ion in a metallic lattice and a 'sea' of delocalized electrons
• explain in terms of bonding and structure how metals conduct electricity?

  delocalized electrons can carry the current
• explain in terms of bonding and structure how metals are malleable and ductile?

  layers of ions can slide over each other
• why do all isotopes have an overall charge of zero?

  same number of protons and electrons