Elements

Elements, Atoms and Atomic Structure

Elements

  • Substance which is made up of one type of atom (Pure Substance)

  • Cannot be broken down into simpler substances [can be broken down into singular atoms]

  • E.g. Gold/Au, Helium/He

Compounds

  • 2+ different atoms together in a specific ratio

  • cannot be separated unless chemically

  • E.g. H2O

Atoms

  • Make up everything around you

  • Electron, proton, neutron

  • Proton + neutron makes nucleus

Protons/Electrons/Neutrons

  • Protons have 1800x mass

  • Electrons have 1x mass

  • Neutrons have 1800x mass

Isotopes

  • same type of atom with different amount of neutrons in nucleus

Electron Configuration

Electrons

  • No. of electrons is equal to No. of protons in an atom

Electron Shell

  • Electrons are found in the electron cloud which is surrounding the nucleus of the atom.

  • The cloud is made of different shells which can ‘hold’ a different amount of electrons

  • E.g. 1st - 2, 2nd - 8, 3rd - 8, 4th - 16, etc

  • Electrons are attracted to the nucleus due to the protons positive charge which keeps the electrons from floating away.

  • Electrons can be gained or lost due to the force of attraction between the nucleus and electron of one atom and the force of another atom

  • No. of electrons in each shell in the electron configuration

  • E.g. Sodium/Na, 11 electrons, 2.8.1

Position of an Element in the Periodic Table

  • Horizontal rows are called periods and go from 1-7 which means they have similar physical properties, it is also the same as amount of electron shells the atom has

  • Vertical columns are called groups and go from 1-18 which presents the allocated group they are in such as the main ones alkali metals, alkaline earth metals, transition metals, halogens and noble gases which are grouped based on the amount of electrons in their valence shell and the reactivity of the element.

  • Last digit of group number is amount of valence electron in valence shell

Reactivity

  • Outermost shell of an electron is called the valence shell which contains valence electrons

  • The higher mass of electrons in valence shell the more stable the element

  • To obtain full valence shell atoms must chemically bond with other atoms to gain/lose/share valence electrons

  • The most reactive elements are generally the ones who need to gain or lose 1 or 2 electrons to have a full valence shell

Dmitri Mendeleev - Construction of Periodic Table

  • `elements have properties that recur or repeat according to their atomic (weight) [number]’

  • Prof. Moseley changed Mendeleev’s statement as seen above from weight to number as the atomic weights can change due to the no. of neutrons in the element but the atomic no. won’t as the protons will stay the same.

Groups

Hydrogen

  • non metal

  • 1 electron in shell

  • very flammable

  • diatomic reactive gas

Alkali Metals

  • reactive to water

  • conduct electricity

  • soft and silvery

  • low melting point

  • low density

  • 1 extra electron

  • Group 1

Alkaline Earth Metals

  • white and malleable

  • reactive but less than 1st group

  • conduct electricity

  • Group 2

Halogen family

  • non metal

  • very reactive

  • often bonds with group 1 elements

  • 1 short on electrons

  • form diatomic molecules

  • toxic and lethal

Noble Gases

  • non metal

  • full valence shell

  • not reative

  • gas

  • stable

  • low boiling point

  • no colour/odour/flavour

  • not flammable

  • low pressure

  • low electricity conduction