matter

• atom 


  the smallest part of an element that can exist
• atomic number


  is the number of protons in an atom which is also equal to the number of electrons
• compound

  a substance made of 2 or more atoms chemically combined together
• relative atomic mass


  an average value that takes account the abundance of the isotopes of the elements
• periodic table


  table of elements arranged in order of atomic number and elements with similar properties are in the same group
• Each group contains elements with similar properties
• All atoms are made of a central nucleus with electrons orbiting
• The charge on the electrons is the same size as the charge on the protons
• Electron mass is 1/1837
• Crystallisation is used to produce solid crystals from a solution leaving crystals behind
• atoms make up all substances and are the smallest part of an element that can exist
• chemical symbols represent an atom of an element
• compounds are formed from elements by chemical reactions
• Chemical reactions always involve the formation of one or more new substances
• compounds contain two or more elements chemically combined in fixed proportions and are represented by formulae
• compounds can only be separated by chemical reactions
• A mixture consists of two or more elements or compounds not chemically combined
• the chemical properties in a mixture are unchanged
• mixtures can be separated by physical methods such as filtration , crystallisation simple distillation , fractional distillation , and chromatography
• ancient greeks were first to have ideas about atoms
• John Dalton in the 1800s said that atoms were tiny hard spheres, and that each chemical element had different atoms that varied in mass. he believed they could not be spilt or divided
• atomic number is the number of protons in an atom of an element.
• all atoms of an element have the same number of protons in their nucleus
• atoms have a radius of 0.1 nanometres and a mass of 1 x 10^-27 kg
• mass number is the sum of protons and neutrons
• isotopes are the same element with different numbers of neutrons
• electrons occupy the lowest available energy levels
• elements are arranged in order of atomic number in the periodic table.
• elements in the same periodic group have the same number of electrons in their outer shells
• the periodic table is named this because elements with similar properties occur at regular intervals
• knowledge of isotopes explained why elements cant be arranged by atomic weights
• metals form positive ions
• alkali metals react vigorously with water to create an alkaline solution and hydrogen gas
• group one metals react with oxygen to form an oxide
• the reactivity of group one elements increases as you go down the group
• when group one elements react with chlorine they form a white precipitate
• noble gases all have full outer shells
• they are unreactive and do not easily form molecules
• the boiling points of noble gases increase as you go down the group along with the atomic mass
• the halogens exist as molecules