General Chemistry Section 2 Definitions

Law of constant composition

A given compound relative numbers and kinds of atoms are constant

Law of conservation of mass

The total mass after a chemical reaction is the same as the total mass before

The Law of multiple proportions

whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers

Isobars

same number of nucleons (protons and neutrons) but different number of protons

Isotopes

Atoms of the same element that have the same atomic number, identical properties but different masses & physical properties

Radioactive decay

unstable nucleus transformed into a more stable one

Nuclear transmutation

nuclei change as a result of bombardment by neutrons, electrons or protons

Nuclear fission

heavy nucleus splits into two lighter ones

Nuclear fusion

two light nuclei fuse into a heavy one

Alpha radiation

emission of alpha particles, only for heavy nuclei, shielding required paper

Beta radiation

emission of an electron, mass number constant --> atomic number +1 as neutron transformed into proton, shielding required foil

Gamma radiation

very low wavelength = high energy, shielding required massive walls of lead

Use of radioactivity

Radiometric dating, medicine, maintenance-free sources of energy, sterilization, chemistry

Wavelength

The distance between two wave crests or troughs

Frequency

the number of waves that pass a point per second

Amplitude

intensity of radiation

Quantization of energy (Planck)

E = hν = hc/λ , assuming energy does not continuously increase

Photoelectric effect

The emission of electrons from a metal when light shines on the metal

Bohr's Model

(1) only orbits with certain radii/energies are allowed

(2) an electron in an allowed orbit does not emit energy

(3) energy is emitted or absorbed (E = hν) when the electron changes orbit

Negative of Bohr's Model

only works for 1 electron atoms, electron should loose energy and fall into nucleus, violates Heisenbergs uncertainity.

Heisenberg uncertainty principle

the position of an electron cannot be determined exactly; only a probability density can be given.

Schrödinger equation

An equation that describes electron as a standing wave; its solution is the wave function ψ.

Wave function ψ

solution of the Schrödinger equation

ψ²

probability or electron density

Radial probability function

4πr²·ψ²

Orbital

region described by ψ

principle quantum number

n = shell/orbital

Angular momentum quantum number

l = subshell

Magnetic quantum number

mL = orientation of the orbitals , characterises the energy in an external magnetic field (Zeeman effect).

Spin quantum number

mS = spin , electrons in one orbital must have different spins

S-Orbital

spherical, 0 node

P-Orbital

dumbbell shaped, 1 node

D-Orbital

clover shaped, 2 nodes

F-Orbital

complex geometry, 3nodes

Pauli principle

each electron is uniquely characterised by n, l, mₗ, mₛ

Degenerate

atoms of identical energy