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Atoms and isotopes GapFill
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The idea of an atom as a component of matter was first proposed by the ancient Greeks.
Thousands of years later, the first subatomic particle, the , was discovered, which is a negatively charged particle, much smaller than the mass of even the lightest atom. This led to J J Thomson proposing a model of the atom called the model, which had these negative particles dotted through a larger ball of positive charge.
A scientist called Ernest Rutherford tried to prove Thomson's model right by shooting alpha particles at gold foil. Most alpha particles passed straight through the atoms making up the gold foil with only slight deflections, while some got deflected back at the alpha source – this didn't match Thomson's model at all! In fact, it suggested that most of the mass and all of the positive charge of the atom were concentrated in a small point at the centre of the atom, called the . It was later found out by both Ernest Rutherford and James Chadwick that this positive central mass was made up of particles called , and is times the size of the atom.
A scientist called Niels Bohr proposed that electrons orbit this central positive mass at distinct distances called . Electrons can move between them by absorbing or emitting .
Atoms of the same element have the same number of , which is known as the atomic number of the atom. The mass number of the atom is the number of in the atom.
Atoms of the same element can have different numbers of – these variations of one element are called isotopes.
Thousands of years later, the first subatomic particle, the , was discovered, which is a negatively charged particle, much smaller than the mass of even the lightest atom. This led to J J Thomson proposing a model of the atom called the model, which had these negative particles dotted through a larger ball of positive charge.
A scientist called Ernest Rutherford tried to prove Thomson's model right by shooting alpha particles at gold foil. Most alpha particles passed straight through the atoms making up the gold foil with only slight deflections, while some got deflected back at the alpha source – this didn't match Thomson's model at all! In fact, it suggested that most of the mass and all of the positive charge of the atom were concentrated in a small point at the centre of the atom, called the . It was later found out by both Ernest Rutherford and James Chadwick that this positive central mass was made up of particles called , and is times the size of the atom.
A scientist called Niels Bohr proposed that electrons orbit this central positive mass at distinct distances called . Electrons can move between them by absorbing or emitting .
Atoms of the same element have the same number of , which is known as the atomic number of the atom. The mass number of the atom is the number of in the atom.
Atoms of the same element can have different numbers of – these variations of one element are called isotopes.