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According to J.J. Thomson’s atomic theory and plum-pudding model, atoms consist small particles called electrons, which were negatively charged, and positive charges around the entire atom. According to Thomson after he discovered electron in cathode rays, the model of the atom is a lot like a plum-pudding where the raisins represent electrons in the pudding which represents positive charges spread out across the atom. This shows that since the atom is electrically neutral, Thomson predicted that there has to be positively charged particles in the atom to balance out the negative charge of the electrons, which he knew were already in the atom.
According to Neils Bohr’s atomic theory, an atom consists of electrons on different energy levels orbiting the nucleus. According to Bohr’s theory, electrons can only have stable orbits around the nucleus if they move in orbits with different sizes and quantized energy levels. This shows that electrons in a certain energy level can only have that definite amount of energy. If an electron were to have more or less energy than the energy level it is on, it would give out or take in energy depending on whether it jumped to a higher or lower energy level. For example, when an electron jumps to a lower orbit, it has to give off energy equivalent to the different between the two orbits. When an electron jumps to a higher orbit, it then has to absorb energy equivalent to the different between the two orbits. The emission and absorption of energy can be seen on a emmission and absorption hydrogen spectrum. This allowed him to develop his Bohr Model, which shows which energy level each electron is on.
According to John Dalton’s atomic theory, an atom is a small, particle that consists of different masses and properties based on its element. According to Dalton, his theory consisted of four postulates:
1. All matter consists of very small particles called atoms
2. An element consists of atoms of one type only
3. Compounds consists atoms more than one element and are formed by combining atoms in whole-number ratios
4. In a chemical reaction atoms are not created or destroyed
His second postulate states that an element consists of only one type of atom, which shows that the atoms of each element is different. However, the atoms of an individual element contain similar masses and properties, which is why they form the same element.
Democritus and Leucippus were Greek philosophers who were the first to propose an atomic theory, which was the theory of an atom. With a model called the hard sphere model, they proposed that atoms are solid, homogeneous particles that make up all matter.
Sir James Chadwick was a British physicist who discovered the positively charged particles in the nucleus of an atom called neutrons. He did this with an experiment similar to the gold foil experiment where he hit beryllium with alpha particles in a vacuum chamber, which then emitted neutrons.
John Newlands was an English chemist who organized the periodic table by the law of octaves. This law stated that there was a pattern with the properties every 8th element when the elements were organized by their atomic weight.
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According to Ernest Rutherford’s atomic theory, an atom is mostly empty space but has a dense positively charged center called the nucleus. According to Rutherford’s gold foil experiment, when a gold metal foil was hit with alpha particles, some beams of particles went through the foil, while others were deflected or even bounced back. This shows that Thomson’s plum-pudding model was incorrect about the positively charged particles. Instead of the particles being spread out across the atom, Rutherford’s gold foil experiment proved that the positive charge is actually located in the center of the atom which is why the majority of alpha particles passed through the gold foil but a few beams were deflected.
Dmitri Mendeleev organized the periodic table by order of the elements’ atomic weight to identify the pattern of their properties. According to Mendeleev, his organization of the periodic table by the periodic law, allowed him to observe repeated patterns between the properties of the elements. This shows that with this new organization technique, Mendeleev would be able to predict existing elements that have not been discovered yet and its properties. However there were some flaws in his organization as some elements did not follow the pattern.
Johann Dobereiner was a German chemist who organized the periodic table by the law of triads. This law stated that there was a connection between the atomic weight and different elements, which occurred in groups of three.
Henry Moseley arranged the periodic table in order of an element’s atomic number to get rid of problems from previous organization methods. According to Moseley, his organization of the periodic table was based on the modern periodic law. This shows that the periodic table would be more organized as this way, the elements were organized by their properties due to the arrangement of increasing atomic numbers. This version of the periodic table is also the one we use today.