atomic structure

• atoms contain...


  protons, neutrons and electrons
• atom size


  1x10^-10
• nucleus


  - middle of the atom

  - contains protons and neutrons

  - has a radius of 1x10^-14 (1/10000 of the radius of an atom)

  - has a positive charge due to protons

  - almost the whole of the mass of the atom is concentrated here (atom's relative mass)
• proton


  - particle with positive charge

  - relative charge of +1

  - relative mass of 1

  - amount of protons in an atom is the atomic number
• neutron


  - particle with no charge

  - relative charge of ±0

  - relative mass of 1
• electron


  - particle with negative charge

  - relative charge of -1

  - relative mass of 1/1836

  - moves around the nucleus in electron shells

  - small but cover a lot of space

  - volume of orbit determines atom's size
• electronic structure


  the arrangement of electrons in an atom or molecule
• electron shell rules


  - electrons always occupy shells

  - the lowest energy levels are always filled first (the ones closest to the nucleus)

  - only a certain number of electrons are allowed in each shell...

  1st: 2, 2nd: 8, 3rd: 8...

  - atoms are non-reactive when they have a full electron shells

  - in most atoms, the outer shell is not full, making the atom reactive to fill it

  - further from the nucleus = high energy
• how do electrons change energy levels?

  by absorbing (moving from a low energy level to a higher one) or emitting electromagnetic radiation (moving from a high energy level to a lower one)
• nuclear model


  model of the atom with a nucleus containing protons and neutrons (with most of the atoms mass compressed into it) and with electrons in the space outside the nucleus (with mostly empty space between electrons and the nucleus)
• nuclear symbol


  atomic number and mass number
• atomic number


  the number of protons in the nucleus of an atom
• mass number


  the sum of the number of neutrons and protons in an atomic nucleus
• element


  a simple substance that cannot be broken down into smaller parts or changed into another substance
• elements consist of atoms with the same...

  atomic number
• isotopes


  different forms of the same element, which have the same number of protons but different number of neutrons
• Isotopes have the same ... but different ...

  atomic number, mass numbers
• relative atomic mass (Ar)

  an average mass taking into account the different masses and abundances of all the isotopes that make up the element
• relative atomic mass formula

  Sum of (isotope abundance x isotope mass number) / sum of abundances of all the isotopes
• when elements react, atoms join together to make...

  compounds
• compounds


  - substances formed from two or more elements

  - the atoms are in fixed proportions and held together by chemical bonds

  - a chemical reaction is needed to separate the original elements as it hard to do so

  - properties of a compound are usually totally different from the properties of the original elements
• a compound formed from a metal and a non-metal consists of...

  ions

  - the metal atoms lose electrons to form positive ions

  - the non-metal atoms gain electrons to form negative ions

  - these opposite charges mean that they are strongly attracted to each other (ionic bonding)
• ions


  positively and negatively charged atoms
• ionic bonding


  the electrostatic attraction between oppositely charged ions
• a compound formed from non-metal consists of...

  molecules
• molecules


  - groups of two or more atoms held together by chemical bonds

  - each atom shares an electron with another atom (this is called covalent bonding)
• covalent bonding


  a bond formed when atoms share one or more pairs of electrons
• a formula shows...


  what atoms are in a compound
• chemical changes are shown using...

  chemical equations
• symbol equations show...


  the atoms on both sides
• symbol equations need...


  to be balanced
• mixtures are easily...


  separated
• mixtures


  - a combination of two or more substances that are not chemically combined

  - the parts of a mixture can either be elements or compounds

  - can be separated out by physical methods such as filtration , crystallisation, simple distillation, fractional distillation and chromatography

  - the properties of the mixture are just the properties of the mixture's separate parts (the chemical properties of a substance aren't affected by it being part of a mixture)
• paper chromatography


  method of separating a mixture of different colours
• paper chromatography method


  - spots of ink or plant dye are placed on a pencil line

  - as the paper is lowered into the solvent, some of the dye spreads up the paper

  - the paper has absorbed the solvent, and the dye has spread further up the paper
• filtration


  a technique that uses a porous barrier to separate a solid from a liquid
• filtration method


  - one beaker contains a mixture of solid and liquid, the other contains a funnel with filter paper

  - the solid and liquid mixture is poured into the filter funnel

  - the liquid drips through the filter paper but the solid particles are caught in the filter paper
• crystallisation


  a separation technique used to produce solid crystals from a solution by evaporating the solvent
• crystallisation method


  - a solution is placed in an evaporating basin and heated with a Bunsen burner

  - the volume of the solution has decreased because some of the water has evaporated. Solid particles begin to form in the basin

  - all the water has evaporated, leaving solid crystals behind
• simple distillation


  used to separate a liquid from a solution