Chemistry - Structure (1.1-1.5)

Law of conservation of mass

In chemical reactions, matter cannot be created or destroyed

Element

Atoms which have same number of protons

Compound

A fixed ratio of differing atoms

Homogenous

A mixture with uniform composition

Heterogenous

A mixture with non-uniform composition

Isotopes

Atoms of the same element with differing number of neutrons

Continuous spectrum

Contains light of all wavelengths and appears as a continuous series of colour

Absorption Spectra

When electrons excite energy levels, leading to an absorption of energy from photons, leading to missing bands of colours in the continuous spectrum.

Emission Spectra

When electrons fall from an excited state, leading to an emisssion of energy, leading to specific bands of colour emitting from the continuous spectrum glowing.

Postulates of Neil Bohr’s Hydrogen Spectra

1. Electrons exist at discreet energy levels

2. Energy levels converge at higher energies

   1. Colors are produced when electrons transition to lower energy levels, and colours are absorbed when electrons are excited.

Aufbau Principle

Electrons fill the lowest energy levels first

Pauli exclusion principle

An orbital can hold a maximum of 2 electrons with opposite spins

Hund’s Rule

One electron must be in each sublevel before doubling up

Ionization Energy

The minimum energy required to eject an electron out of a neutral atom or molecule in its ground state.

Solutions

Homogenous mixtures of two or more components

Concentrated solution

Contains a large proportion of solute, and so has a high ratio of solute to solvent

Filute solution

Has a small proportion of solute, and has a low ratio of solute to solvent

Molar connection/Molarity

Ratio of the amount of a solute to the volume of the solution