atoms Flashcards
father of the atom
John Dalton
founder of electrons
- JJ Thompson
- created plum pudding
founder of nucleus and protons
Rutherford
founder of electron configuration
Bohr
founder of neutron
Chadwick
how are electrons held within the cloud surrounding the nucleus
held together by electrostatic forces of attraction between the positive nucleus and negative electrons
isotopes
elements with the same number of protons but different number of neutrons
isotopes have …
identical chemical properties (same electron config.) but different physical properties (mass, density, colour)
stable and unstable isotopes
stable: when there is a balance of attractive and repulsive forces in the nucleus
unstable: when these forces are unbalanced
- radioactive decay will occur as the nucleus is unstable
- releasing high energy particles or radiation
relative atomic mass formula
mass number = (percentage x a-mass) + (percentage x a-mass) / 100
the ability of atoms to form chemical bonds can be explained by …
- the arrangement of electrons in the atom and in particular by the stability of the valence electron shell
mass spectrometry
1) ionisation: high-energy electrons removes an electron from the atom giving them a +charge
2) acceleration: these +ions are accelerated through an electric field so that they are moving at high speed
3) deflection: ions are then deflected by a magnetic field according to their masses.
- Lighter ions are deflected more, the heavier they are: the less they are deflected
4) detection: detectors can measure the abundance of ions that strike them (giving qualitative data)
- this info can then be transferred to a mass spectrum
electron configuration
- electrons circled around the nucleus at fixed distances and only exist in certain energy levels
- electrons can jump from a low level to a high level when they gain energy (heat)
- electrons can drop from a high level to a low level when they lose energy (light)
- core electrons have low energy levels
- valence electrons have high energy levels
core charge
- measure of the attractive force felt by the valence electrons towards the nucleus
- inner shell electrons are said to be ‘shielding’ the valence electron from the full attraction of the nucleus
= #protons - #inner shell electrons
- across periods: increases
- down groups: remains constant
atomic radius
- distance from the nucleus to the valence-shell electron
- across periods: decreases (CC increase making them smaller)
- down groups: increase (higher energy levels are further away)
ionisation energy
- is the energy required to remove one electron from an atom of an element in it’s gaseous state
- 1st IE = 1st valence electron removed
- across periods: increases (CC increases requiring more energy to remove the electron)
- down groups: decrease (AR increases, electrons are further away)
electronegativity
- the ability of an atom to attract a pair of electrons in a covalent bond to its self
- across periods: increases (CC increases, incoming electrons will be attracted more strongly)
- down groups: decreases (AR increases, incoming electrons are not attracted as strongly)
metalloids
are located between metal & non-metals
bonds
metallic: metal with metal
ionic: metal with non-metal
covalent: non-metal with non-metal
element
a substance made up atoms with the same atomic number
compound
a pure substance made up of different types of atoms in a fixed ratio
mixture
different substances, not chemically joined with no fixed ratio
physical properties
properties can be determined without changing the chemical composition of the substance
chemical bonds …
can be explained by the arrangement of electrons in the atom
- in particular by the stability of the valence electron shell
