Chapter 1: Atomic structure and the periodic table Flashcards
How were elements first sorted and categorised?
Relative atomic mass (protons, neutrons and electrons had not yet been discovered)
What did John Newlands discover?
The properties of elements seemed to repeat every 8th element (law of octaves) when they were sorted by atomic weight. He observed that lithium, potassium and sodium has similar properties
Why was John Newlands’ periodic table not accepted?
Only worked for the first 20 elements. After that there were problems, such as copper being in the same group as sodium
How was Mendeleev’s periodic table different to Newlands’?
Mendeleev left gaps for elements he thought would be discovered in the future. He also swapped some of the elements around so that they were in more appropriate groups (he thought that the atomic weights must have been measured incorrectly)
Why was Mendeleev’s table accepted?
Elements were later discovered that Mendeleev predicted would exist, and their properties matched his predictions. We now know that Mendeleev placed the elements in order of atomic number (number of protons), even though he didn’t know about protons
How was the nuclear model of the atom discovered?
Geiger and Marsden directed a beam of alpha particles at a thin sheet of gold foil. They thought the gold atoms were like Professor Thompson’s plum pudding model (weak positive charge all throughout), so they expected the alpha particles to pass straight through the foil. They realised that a small number actually bounced back. Rutherford produced a theory to explain this
What was Rutherford’s theory?
He suggested that the deflection of an alpha particle was caused by the electrostatic interaction between it and a small, charged nucleus. He suggested that the nucleus could either be positively (would repel an alpha particle backwards) or negatively charged (would pull the alpha particle around it)
What is the Bohr model of the atom?
A model of the atom suggested by Niels Bohr in which elections move around the nucleus in circular orbits, and can change their orbits by releasing or absorbing electromagnetic radiation
Who discovered neutrons?
James Chadwick in 1932. His discovery allowed scientists to account for the mass of the atom
Why does alpha scattering happen?
Most of the atom is empty space (diameter of an atom is 20000x the diameter of the nucleus), so the majority of alpha particles pass straight through without getting near the nucleus. Some approach the nucleus head-on and deflect the way they came, and some pass near the nucleus and their direction changes. Later experiments showed that the nucleus could be further subdivided into smaller particles (protons)
How were electrons discovered?
In 1897, J J Thompson discovered that electrons were emitted from the surface of hot metals. He showed that electrons were negatively charged and much smaller then atoms. This led to a change in the accepted atomic theory
What is the plum pudding model?
The model for the atom proposed by Thompson in 1904 that states that atoms were made up of a ball of positive charge with negative electrons inside it
