electron structure

• how does an atom become an ion?

  by gaining or losing electrons
• what is a cation?


  positively charged ion (lost electrons)
• what is an anion?

  negatively charged ion (gains electrons)
• how many kinds of orbitals are there? what are they?

  - 4

  - s, p, d and f orbitals
• how many electrons can an orbital accomodate?

  can accomodate 2 electrons with opposite spins
• s- orbital


  - spherical shape

  - found in every energy level
• p- orbital


  - double tear drop shape

  - three found in energy level 2 and onwards
• Aufbau Principles

  - n² orbitals in the nth energy level

  - energy level can accommodate a maximum of 2n²
• energy level diagram format

  
• valence electrons


  the electrons that occupy the outermost energy level of an atom. They are involved in bonding
• core electrons

  the electrons that occupy the inner energy levels. They shield the valence electrons from the attraction of the positive nucleus
• shielding


  the effect on an electron of repulsion by electrons in lower-energy orbitals that screen it from the full effects of nuclear charge
• what is the atomic diameter?

  the distance between the nuclei of two touching atoms

  - radius = distance/2
• bond length


  the distance between the nuclei of two atoms
• atomic size trend

  - As you go across a period, decreases

  - As you go down a group, increases
• why does atomic size follow such a pattern across a period?

  - as you move across the charge of the nucleus increases, this causes the electrons to be pulled closer to the nucleus causing the atomic radius to decrease. valence electrons close to nucleus= smaller atomic size
• why does atomic follow such a pattern along a group?

  - as you go down a group the number of energy levels increases within the atom, increasing the shielding effects of the core electrons. the valence electrons are therefore not attracted as strongly by the nucleus = larger atomic size
• ionisation energy


  the ionisation is the minimum amount of energy required to remove an electron from an atom in the gas form
• Why are valence electrons important?

  They are involved in bonding; determine the reactivity of an element

  - they are removed first as they feel the attractive force of the nucleus the least and are easiest to remove.
• what factors affect ionisation energy?

  - atomic radius-->smaller atoms hang onto their valence electrons more tightly and so have higher ionisation energies

  - nuclear charge--> the higher the positive charge of the nucleus, the harder it is to pull away additional electrons
• ionising energy trend


  - as you move across a period, the first ionisation (energy required to remove the first electron) energy increases

  - as you move down a group, the first ionisation (energy required to remove the first electron) energy decreases
• why does ionisation energy follow such a pattern across a period?

  - as you move across the charge of the nucleus increases, this causes the electrons to be pulled closer to the nucleus causing the atomic radius to decrease. valence electrons close to nucleus= high energy needed to remove electrons
• why does ionisation energy follow such a pattern along a group?

  - as you go down a group the number of energy levels increases within the atom, increasing the shielding effects of the core electrons. the valence electrons are therefore not attracted as strongly by the nucleus = less energy to remove electrons