Atoms

basic unit of a chemical element

• Greek philosopher Democritus proposed that all matter can be decided into smaller pieces until there is a single indivisible particle is reached (~400 BCE)

• Aristotle rejected the idea of an atom and state that everything is made up of earth, water, air and fire and they were either dry, wet, cold or hot (~450BCE)

• John Dalton proposed that all matter is made up of particles called atoms and all atoms of an element are the same, and atoms of different elements are different

• Atoms are also believed to be rearranged to for new substances in chemical reactions but don’t create nor destroy any previous ones (1807)

• J.J Thompson discovered that small negatively charged particles could be emitted by very hot materials and are attracted to the positive ends of a circuit.

• Positive and negative charges were known to attract each other, therefore he concluded that these particles must be negatively charged and Thomas called them electrons

• Thomas’s model was called “plum pudding”

• Ernest Rutherford tested Thompson’s model and predicted that of positive and negative charges were distributed throughout atoms, then tiny positively charged particles shot at a thin piece of golden foil would pass through the foil

• In Rutherford’s revised model, the center of the atom has a positive charge, the center is called the nucleus, which contains most of the atom’s mass but occupies a very small space

• The nucleus is what made some particles bounce back siring the experiment

• The suckers is surrounded by a cloud of negatively charged electrons of an atom and has employ space between them

• Bohr says that electrons orbit the nucleus and each electron in an orbit has a definite amount of energy

• The farther the election from the nucleus, the greater the energy

• Electrons can not be between orbits but can jump from orbit to orbit (but do note that there is no specific course that an electron must take and that it is random and different every time, but it can still jump to another electron’s orbit instead)

The number of protons and neutrons are the same and electrons can vary. But the number of rings depends on the amount of electrons it has. The ring number cap goes “2, 8, 8, 18…”. Every element also starts off neutral, but then later gains charges by losing (becomes positive) or gaining (becomes negative) elections. This happens because all of the elements want to be stable. Which means having the desired amount of electrons on its outermost shell (which is the maximum amount).

Reading the periodic table:

• The atomic number identified the element, number of protons in the nucleus and number of electrons in a neutral atom

• The mass number of an atom in AMU (atomic mass units) and it can be used to find the number of neutrons

• Number of neutrons = Mass Number - Atomic Number

• Organized by atomic number

• Lightest have the lowest numbers

Equations:

Groups:

Alkali metals:

• Group 1

• Very reactive

• Not found naturally as pure elements

Alkaline earth metals:

• Group 2

• Fairly reactive metals

• Not as reactive as group 1

Halogens:

• Group 17

• Toxic

• Reactive

Noble gasses:

• Group 18

• Completely non-reactive

• All gasses

• Found in atmosphere as pure elements

Keywords:

Scientific theory — an expression of our best understanding of a phenomenon, based on scientific reasoning and/or evidence

Protons — a positively charged particle that is found in an atom’s nucleus

Neutrons — a neutrally charged particle that is found in an atom’s nucleus

Electrons — a negatively charged particle circling around the atom’s nucleus