Atomic Models And Experiments:
The earliest model of an atom (Thomson Model) proposed that an atom is an indivisible hard sphere.
Gold foil experiment discovered that most of the atom is empty space and inside an atom there is a small, dense, positively charged nucleus.
Bohr model stated that protons are inside a nucleus and electrons revolve around the nucleus in orbits.
Wave Mechanical model defined an orbital is as a region of the most probable electron location
What we need to know about an atom and subatomic particles
protons have a +1 charge
neutrons have no charge
electrons have a -1 charge
protons and neutrons are located inside the nucleus
electrons are located outside of the nucleus
protons are neutrons have a much larger mass than that of an electron
to calculate the charge of an ion we add positively charged protons and negatively charged electrons. For example if an ion has 3 protons and 4 electrons, we calculate +3-4=-1. -1 is the charge of this ion.
Atomic mass = protons +neutrons
Atomic number = number of protons. Atomic number represents the identity of an element.
In a neutral atom, the number of protons and electrons is equal.
Isotopes are atoms of the same element (same number of protons) that have a different mass (different number of neutrons).
Electron configuration shows how many electrons are in each energy level(shell) of an atom. For example 2-8-8-2 means there are 2 electrons in the first shell, 8 in the second shell, 8 in the third shell and 2 in the fourth shell. Electron configuration of each element is shown on the Periodic Table.
When an electron gets excited (absorbs energy), it moves from a lower to a higher energy level.
When an electron moves from a higher to a lower energy level, it releases energy.
Bright Line Spectra
When excited electrons move back to lower energy levels, energy is realizes in the form of light which is shown as bright-line spectrum. Every element has its own bright-line spectrum.
Valence electrons are outer shell electrons. They are the last electrons in the electron configuration of an atom. For example, an element with electron configuration of 2-8-6 has 6 valence electrons.
Lewis dot structure shows the symbol of the element and dots around the symbol, representing the number of valence electrons this element has.
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