Chemistry Chapter 2: Electrons in atoms

  CHEMISTRY KEYWORDS: 

Successive ionization energies: The energy required in each step to remove the first electron, then the second, then the third, and so on, from a gaseous atom.

Shielding: The ability of inner shell electrons to reduce the effect of the nuclear charge on outer shell electrons.

Sub-shells (subsidiary quantum shells): Regions of the principal quantum shells where electrons exist in defined areas associated with particular amounts of energy. They are named s, p, d, etc.

Spectroscope: When high-speed electrons hit gas particles at low pressure, coloured lines are seen through an instrument.

Atomic orbitals: Regions of space outside the nucleus that can be occupied by a maximum of 2 electrons. Orbitals are named s, p, d, and f. They have different shapes.

Free radical: A species with one (or sometimes more than one) unpaired electron.

Spin-pair repulsion: A pair of electrons in the same orbital repel each other because they have the same charge. Pairing the spinning electrons so they spin in opposite directions reduces the repulsion. The repulsion is more than that of single electrons in separate orbitals. That is why the electrons in the p and d orbitals go into separate orbitals before being paired up.

Atomic radius: The covalent atomic radius is half the distance between the nuclei of two covalently bonded atoms of the same type. This is not the only type of atomic radius but it gives us the best data when comparing the elements across a period.

CHEMISTRY DEFINITIONS:

Energy levels: Each electron in an atom has it particular average amount of energy. The further away the electron is from the nucleus, the more energy it has. Each principal energy level (symbol n) corresponds to an electron shell at a certain distance from the nucleus. Energy levels are split up into sub-levels which are given the names s, p, d, etc.

Electronic configuration: A way of representing the arrangement of the electrons in atoms showing the principal quantum shells, the sub-shells, and the number of electrons present. The electrons may also be shown in boxes.

First ionization energy, IE₁: The energy needed to remove 1 mole of electrons from 1 mole of atoms of an element in the gaseous state to form 1 mole of gaseous ions.

CHEMISTRY IMPORTANT NOTES:

Ionization energy increases as the proton number increases.

The further the outer electron shell is from the nucleus, the lower the ionization energy.

The ionization energy is lower as the number of full electron shells between the outer electrons and the nucleus increases.

S – 1 orbital, P – 3 orbitals, D – 5 orbitals

SUMMARY:

Electron shells can be divided into s, p and d sub-shells which can hold a maximum of 2, 6 and 10 electrons respectively, and each sub-shell has a specific number of orbitals which can each hold a maximum of 2 electrons.

The first ionization energy of an element is the energy needed to remove one electron from each atom in one mole of atoms of the element in the gaseous state (to form gaseous +1 ions).

The magnitude (how big the value is) of the ionization energy depends on 4 things:

• The distance of the electron from the nucleus.
•  The number of positive charges in the nucleus.
• The degree of shielding of outer electrons by inner electron shells.
•  Spin-pair repulsion.

The electronic configuration of the outer shell electrons and the position of an element in the Periodic Table can be deduced using successive ionization energy data.