Atomic Structure and the Periodic Table

Question 1

Atoms

Answer 1

Relative mass- P=1, N=1, E= Very small
Charge- P=+1, N=0, E=-1
Atomic number= amount of protons
Mass number= total number of protons and neutrons
Neutrons= Mass number- atomic number

Question 2

Elements

Answer 2

Isotopes- different forms of the same element- different number of neutrons.
Same atomic number, different mass numbers.

Relative atomic mass= sum of (isotope abundance times isotope mass number)/ sum of abundance of all the isotopes.

Question 3

History of the atom

Answer 3

John Dalton- describes atoms as solid spheres, and said that different spheres made up the different elements.
J J Thomson- said atoms weren’t solid spheres. His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles- electrons. The new theory was known as the plum pudding model.
Plum pudding model- atom as a ball of positive charge with electrons spread throughout.
Rutherford- Alpha Particle scattering experiment. Expected the particles to pass straight through because the positive charge was thought of each atom was thought to be evenly spread out. But some deflected- disproving the plum pudding theory.
Nuclear model- Nucleus at the centre- where most of the mass is concentrated. A cloud of negative electrons surrounds the nucleus- so most of the atom is empty space.
Bohr- suggested the nuclear model had electrons contained in shells orbiting the nucleus.

Question 4

Order of discovery- subatomic particles

Answer 4

1897- Electron- Thomson
1920- Proton- Rutherford
1932- Neutron- Chadwick

Question 5

Cathode ray

Answer 5

Neutron- goes straight.
Electron- deflects the most- lightest.
Proton- deflects less- heavier.

Question 6

Mendeleev and the periodic table

Answer 6

Put the elements mainly in order of atomic mass but did switch that order of the properties meant it should be changed.
Gaps were left in the table to make sure that elements with similar properties stayed in the same groups. Some of these gaps indicated the existence of undiscovered elements and allowed Mendeleev to predict what their properties might be.
Discovery of isotopes confirmed he was right to do this.