Chemistry

emisChemistry Notes

3A Exam Revision

Atomic Structure:

* Atomic number= Z = proton or electron

* Atomic Mass= A= protons + neutrons

* Ideal electrons per shell is 2,8,8,8

* Maximum electrons per shell (2n2) is 2,8,18,32 (see Fig 1)

* Energy is required to remove electrons from an atom to overcome the attraction between –ve electrons and +ve protons

* General Ionization Energy: the energy required to remove 1 mole of electrons from an atom or ion

* First Ionization Energy: the energy required to remove the outermost electrons from one mole of an element in its ground state

* Successive Ionization Energy: the energy required is increased as electrons are being removed. More energy is needed as electrons are closer to protons and so have greater attraction (See Fig 2.)

* A significant increase in successive ionization energy represents a change in electron shell.

Periodic Table Trends:

* There are 3 periodic table trends (atomic radius, first ionization energy and electronegativity) that depend on two factors:

1) The number of electrons, and shells occupied

2) Positive charge due to protons

* Atomic Radius:

* Atomic radius of elements increases down the group as 1) more electrons in these elements thus more shells.

* Atomic radius of elements decreases across the period as 2) there are more protons in elements right of the table. More protons means tighter stronger attraction = tighter atom.

* First Ionization Energy:

* First ionization energy of elements decreases down the group as 1) valence electrons are further away from the protons, and more shells block attraction between protons and electrons, thus making the energy required less

* First ionization energy of an element increases across the period as 2) more protons mean stronger attraction, meaning more energy is required to break this

* Electronegativity:

* Electronegativity is a substances ability to attract electrons from...