Atomic Structure Flashcards
(30 cards)
What is an element?
A substance made up of only one type of atom
What is a mixture?
A compound made up of two or more elements that are not chemically linked
What is a compound
A substance made up of two or more chemical elements that are chemically combined
What are atoms
The smallest part of a substance that cannot be broken down chemically
What are molecules
Two or more atoms connected by chemical bonds
Atomic number
(Z)
The number of protons in the nucleus of an atom of an element
Mass number
(A)
Total number of protons and neutrons in the nucleus (nucleon number)
Explain binding energy (BE)
The further the electron is from the nucleus, the less the BE
Outer electrons = weaker attractive forces
Inner electrons= stronger attractive forces
To overcome the forces of attraction of the nucleus and remove and electron
Electron shells
K - 2
L - 8
M - 18
What is valency
The ability of one atom to join another
Ionic bonds
The transfer of electrons from one atom to another forming charged ion
Covalent bonds
Sharing of electrons between atoms
Pauli exclusion principle
No two electrons can be at the same state at the same time within the same matter
What is a nuclide?
A particular variety of atom characterised by a given atomic number and a given mass (an element has a fixed Z and A)
Isotopes
All the atoms of one element must have the same atomic number, but have different mass numbers
They combine with chemicals in the same way
Radioisotopes
Have an unstable nucleus due to the forces of attraction from the neutrons are not enough to bind the nucleus together and outweigh repulsive forces (protons.
The nuclide may breakup or eject radiation energy
Radioactive
Excitation
When an electron moves to a higher energy level and falls back quickly
Emission of electromagnetic radiation
Ionisation
When an electron is ejected from an atom, another electron from a higher energy band falls down to replace the lost electron
Emission of electromagnetic radiation
Explain the band theory
When two or more atoms are in close proximity, their energy levels become modified because their electrons are influenced by the electric fields of both atoms
If many atoms are closely spaced, energy bands are produced
What are the three energy band categories?
Filled bands
Valence Bands
Conduction Bands
What are forbidden gaps?
Separate energy bands
Contain no permitted electrons
Filled band
Energy band bellow valence band
Possess a full complement of electrons
Valence band
Highest energy band with electrons tied to a particular atom
Corresponds to the valence of a single isolated atom
Conduction band
Energy band above valence band
Has free electrons
