The Atom, Bohr’s Theory and Elements. Bohr’s Theory of the Atom. When looking at the light of different elements, we notice they are not the same. Thus, each element emits a very specific pattern of wavelength.
When looking at the light of different elements, we notice they are not the same.
Thus, each element emits a very specific pattern of wavelength.
By noticing these patterns we create the emission spectrum – a pattern of wavelengths emitted by different elements.
Rutherford was very close to finalizing what the atom looked like. It was up to one of his students, Niels Bohr that took Rutherford’s model and perfected it.
Bohr examined the way light was emitted from different elements. He noticed that if he excited an electron and made it move a different light was produced.
He then concluded that he was moving electrons from one orbit to another orbit and thus deduced there are multiple orbits that surround the nucleus of an atom.
Potassium has an atomic number of 19
Observe there are 19 electrons… ohhhhahhhhh!
This is written in Standard Notation
Information about an element includes the mass number, the atomic number and the chemical symbol.
A chemical is written with the chemical name and after it will be the mass number. Example Chlorine - 35
Standard Notation will tell us that Chlorine - 35 has 17 protons, 18 neutrons17 electrons and a mass of 35 g.
Elements tend to have a few different atomic masses, but have the same amount of protons and electrons.
Example Carbon-12 and Carbon-13.
Hmmm what is going on here?
Carbon 12 – has 6 proton, 6 neutrons and 6 electrons and a mass of 12.00. Standard Notation - 126 C
Carbon 13 – has 6 protons, 7 neutrons and 6 electrons and a mass of 13. Standard Notation - 136 C
Even though Carbon-12 and Carbon-13 have different masses because of an extra neutron, THEY HAVE THE SAME CHEMICAL PROPERTIES.
These elements are called Isotopes. A lot of element on the periodic table tend to have quite a few isotopes.
When we charge and atom we call it an ion.
When there are more electrons than protons it has a negative charge and will have a notation of 1-, 2-, 3- and so forth.
When there are more protons than electrons it has a positive charge will have a notation of 1+, 2+, 3+ and so forth.
If you see just a ‘–’ or a ‘+’ symbol that represents 1- or 1+.
Standard Notation for a Chlorine Ion that has a negative one charge
Standard Notation for a Magnesium Ion has a positive 2 charge.
The negative ions are on the right side of the zigzag line of the periodic table up to the noble gases.
The positive ions are on the left side of the zigzag line of the periodic table.
On the periodic table each element has listed: the atomic number, the density at standard temperature and pressure, the most common ion charge, symbol of the element, name of the element and the atomic mass.
The atomic mass is the average of the mass numbers of particular isotopes of an element.
You can determine the mass number of the element by rounding the atomic mass number to the nearest whole number.
Aluminum’s atomic mass is 26.98 (this is the average weight of all its isotopes) and but if we round it to 27 we get its mass.
If we look at Aluminum – it has an atomic number of 13. Thus it is supposed to have 13 protons, 13 neutrons and 13 electrons.
But since Aluminum has an ionic charge of 3+ it must have three more protons than electrons.
Since electrons are easier to move than protons, Al3+ will have 13 protons, 13 neutrons and 10 electrons.
Pg 212 – Questions – 3, 5 (a, c, f, h), 6 (b, d, f), 7, 8, 10
Pg 217 – Questions 1 – 5, 7 – 10, 12, 14, 16, 17