3. Atomic Structure Flashcards
(27 cards)
Democritus
Ancient Greek. First suggested substances were made of atoms. The idea was not accepted.
John Dalton
Ran experiments measuring mass of substances before and after. Proposed that;
1- matter is made of atoms
2- atoms of a particular element are all the same but differ from other elements
3- during chemical reaction atoms rearrange and combine in different molecules
J.J. Thomson
Passed electricity through a tube of gas and found that there were negative electrons produced that must have come from inside the atoms. Proposed a ‘plum pudding’ model where the atom was positive cake with negative electrons stuck like raisins through it.
Rutherford-Geiger-Marsden
Fired positive alpha particles at a thin film of gold and found most passed straight through but some were deflected (repelled). This could only happen if there was a positive nucleus at the centre of the atom.
James Chadwick
Discovered neutrons
Three subatomic particles
Electrons, neutrons, protons
Relative mass of subatomic particles
P= 1, N= 1, E= 0
Relative charge of subatomic particles
P= +1, N= 0, E= -1
Structure of an atom
Dense nucleus in centre containing protons and neutrons. Electrons in orbitals around.
Mass number =
Protons + Neutrons (larger number on periodic table)
Atomic number =
Number of protons (and electrons)
Isotope definition
Atoms of elements with the same number of protons but different numbers of neutrons
Cl-35 (atomic number 17) contains…
17 P, 18 N, 17 E
Cl-37 (atomic number 17) contains…
17 P, 20 N, 17 E
How to calculate relative atomic mass
(mass isotope 1 x abundance) + (mass isotope 2 x abundance) … /total abundance
Relative atomic mass for Cl. Cl-35 = 75%, Cl-37 = 25%
35.5
Relative atomic mass for Br. Br-79 = 50.5%, Br-81= 49.5%
80.0
Arrangement of electrons
In shells. The first shell has 2 electrons, the second 8 electrons. The 3rd can hold 18 electrons
Electron configuration for Mg (atomic number 12)
2,8,2
Electron configuration for K (atomic number 10)
2,8,8,1
Group number tells you…
the number of electrons in the valence (outer) shell
Period tells you…
the number of shells
An element with the electronic configuration 2,8,8 would be in group… and period …
Group 8, period, 3
An element with 16 protons would have the electronic configuration…
2, 8, 6
