Atomic Structure Flashcards
What did John Dalton say about the atom?
He was the first to speak on atoms. At the start of the 19th century, he said that atoms are solid spheres and that the different spheres made up different elements.
What did JJ Thompson say about the atom?
He was the second one to speak on atoms in 1897 saying that atoms aren’t solid spheres as his measurements of charge and mass showed that atoms must contain even smaller, negatively charged particles such as electrons which was called the plum pudding model. It shows that the atom is a ball of positive charge with negative electrons embedded on it.
What did Rutherford say about the atom?
He was the third to speak on atoms saying that the plum pudding was wrong. He thinks that the nucleus is positively charged which is where the mass is concentrated and a ‘cloud’ of negative electrons surround this nucleus so most of the atom is empty space.
What did Neils Bohr say about the atom?
He was the last one to speak on atoms making the nucleus model of the atom which suggested that all electrons were contained in shells. The electrons orbit the nucleus in fixed shells and aren’t anywhere in-between as each shell is a fixed distance from the nucleus.
What is the approximate of a radius of an atom?
≈ 1 x 10⁻¹⁰ m
What is the isotopes of an element?
Atoms with the same number of protons but different numbers of neutrons.
What is the mass number?
Total number of protons and neutrons in an atom.
[number at the top of element]
What is the atomic number?
Number of protons in an atom (equal to charge of nucleus).
[number at the bottom of element]
What is radioactive decay?
When an unstable nucleus decays into another element and gives out radiation to become more stable.
What is ionising radiation (α, β, 𝛾)?
Radiation that knocks electrons off atoms, creating positive ions.
Describe the alpha (α) radiation.
> consists of 2 neutrons and 2 protons (helium nucleus). > absorbed by sheet of paper. > its range in air is a few centimetres. > its ionising power is strong. > it can be used in smoke detectors.
Describe the beta (β) radiation.
> consists of fast moving electron from nucleus.
absorbed by sheet of aluminium.
its range in air is a few metres.
its ionising power is moderate.
it can be used in material thickness testing.
Describe the gamma (𝛾) radiation.
> consists of electromagnetic radiation from nucleus. > absorbed by thick sheets of lead. > its range in air is longer distances. > its ionising power is weak. > it can be used in medical tracers.
What happens to the mass and charge when alpha decay occurs?
Mass decreases by 4 and charge decreases by 2.
[(x) ⟶ (x) + ⁰ -₁e]
What happens to the mass and charge when beta decay occurs?
Mass stays the same but charge increases by one.
[(x) ⟶ (x) + ⁴₂He]
