State the History of the Atom - John Dalton (1766-1844)
- Elements are composed of indivisible particles called atoms
- Atoms of the same element are identical
- Atoms of one element are different to atoms of any other element.
- Atoms of different elements combine in simple whole number ratios to form compounds.
- In chemical reactions atoms are rearranged, separated or combined - NEVER changed.
State the history of the Atom - Joseph Thompson (1856-1940)
- Atoms sometimes eject a far smaller negative particle which he called an electron.
- An atom is made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron’s charge.
State the history of the Atom - Ernest Rutherford (1871-1937)
- Helium nuclei are fired at a piece of gold foil a few atoms thick
- Although most pass through about 1 in 10,000 were deflected
straight back - Proposed a model with a central nuclei of positive charge with orbiting electrons held in place by electrostatic charge
State the history of the Atom - Niels Bohr (1885- 1962)
- Using quantum theory added that the electrons were present in orbits.
- Each orbit can only hold a set number of electrons.
- 2n2
State the history of the atom - James Chadwick (1891-1974)
- A problem with mass
What early ideas are still held as true?
- Element
Single pure substance that cannot be split into another substance - Compound
Chemically combined elements - An atom
Smallest particle of an element - A Molecule
Smallest part of a compound
State the Atomic Structure charge and mass
Proton = 1.602 x 10-19 charge & 1.6726 x 10-27kg
Neutron - no charge & 1.6749 x 10-27kg
Electron = -1.602 x 10 -19 charge & 0.00091 x 10-27kg
Proton +1 & mass number 1
Neutron no charge & mass number 1
Electron -1 & mass number nil
Electron behaviour in subshells
- Electrons always try and obtain the lowest energy state.
- Shells generally fill from inner level outwards.
- Need to be aware of subshells
What is band theory?
- Valence band is the highest range of electron energies in which electrons are normally present at 0oK.
- Conduction band is where the electrons can move freely between atoms.
What is an ion?
- An ion is an atom that has lost or gained an electron.
- Therefore it has an overall charge
- If an electron is removed from an atom it has an overall positive charge
- It is said to have been ionised.
Explain binding energy in relation to potential energy
As binding energy reduces down the subshells from n to k, the potential energy increases from k to n.
What is the unit used for energy?
- The ability to do work
- Unit is the Joule
- eV = electron volt
- 1eV equals approximately 160 zeptojoules (10−21 Joules)
What are the 2 types of energy?
Potential
- Energy by reason of its mass and position or state.
Kinetic
-Energy of a body by reason of its
mass and motion.
What is meant by conservation of energy and mass?
- Energy cannot be lost.
- It can only be converted from one to another.
- Energy has mass equivalence.
What unit is used for power?
- Power is the rate at which work is done
- Unit is the Watt (W)
- 1W = 1Joule per second
State the 3 types of heat transfer
- Conduction - movement of heat within same medium through vibrations.
- Convection - movement of heat within different mediums.
- Radiation - energy can travel without a medium.
What is the equation for heat transfer?
Q=kA ΔT/ Δx
- Q = rate of heat flow
- K = thermal conductivity
- A = cross sectional area
ΔT = temperature difference
——
Δx
