The Atom Flashcards
Dalton’s Model
John Dalton thought of the atom as a solid sphere that could not be divided into smaller parts. His model did not include protons, neutrons or electrons.
The Plum Pudding Model
Scientists’ experiments resulted in the discovery of sub-atomic charged particles. The first to be discovered were electrons- tiny, negatively charged particles
The discovery of atoms led to the plum pudding model of the atom- a cloud of positive charge with negative electrons embedded in it. Protons and neutrons had not yet been discovered.
Alpha Scattering Experiment
Scientists fired small positively charged particles (called alpha particles) at a piece of gold foil only a few atoms thick. They expected the alpha particles to travel straight through the gold. They were surprised that some of the alpha particles bounced back and many were deflected (alpha scattering). To explain why the alpha particles were repelled the scientists suggested that the positive charge and mass of the atom must be concentrated at a small space at it’s centre. They called this space the nucleus.
Nuclear Model
Scientists replaced the plum pudding model with the nuclear model and suggested that electrons orbit (go around) the nucleus, but not at set distances.
Electron shell (Bohr) model
Niels Bohr calculated that electrons must orbit the nucleus at fixed distances. These orbits are called shells or energy levels.
The Proton
Further experiments provided evidence that the nucleus contained smaller particles called protons. A proton has an opposite charge to an electron.
The Neutron
James Chadwick carried out experiments that gave evidence for a particle with no charge. Scientists called this the neutron and concluded that the protons and neutrons are in the nucleus, and electrons orbit the nucleus in shells.
Relative Mass
One property of protons, neutrons and electrons is relative mass- their masses compared to each other. Protons and neutrons have the same mass, so are given a relative mass of 1. It take almost 2000 electrons to equal the mass of a single proton- their relative mass is so small that we consider it as 0.
Atoms and Particles
The Periodic Table lists over 100 types of atoms that differ in the number of protons,neutrons and electrons they each have.
All atoms have equal numbers of protons and electrons meaning they have no overall charge: total negative charge from electrons=total positive charge from protons.
Proton
Relative Charge- +1
Relative Mass- 1
= atomic number
Neutron
Relative Charge- 0
Relative Mass- 1
= mass number - atomic number
Electron
Relative Charge- -1
Relative Mass- 0 (very small)
= same as the number of protons
Elements
Substances made of one type of atom. Each atom of an element will have the same number of protons.
Compounds
Made of different types of atoms chemically bonded together. The atoms in a compound have different numbers of protons.
Isotopes
When atoms of the same element can have a different number of neutrons. Atoms of the same element can have a different number of neutrons, giving them a different overall mass number.
