Published on January 13, 2011
Structure of Atoms
The History and Models of Atoms
Studying Atoms Scientists have been studying atoms since the 1800s. If atoms are too small to be seen, how do we study them? Scientists use models to study atoms. Sometimes scientists can tell what things look like by studying how they act. Example: Wind
Models In science, a model is an idea, a picture, or an object that is built to explain how something else looks or works. The model might not look exactly like the object it is built to describe, but it helps people understand the way the object acts.
History of the Atom Democritus, a Greek philosopher, first used the term atom (atomos) around 400 BC. John Dalton showed that materials were made of atoms in 1803. In the late 1800s we discovered that the atom has many smaller parts. In the late 1800s, English physicist J. J. Thomson discovered the electron. Dalton Thomson
More History of the Atom In 1901 Ernest Rutherford found discovered the nucleus, or center of the atom. In 1917 Niels Bohr, working as Ernest Rutherford’s student, discovered how electrons orbit the nucleus. His model of the atom is the current base for the modern atomic model.
Atomic Mass Unit Subatomic Particles are so small that a special unit was devised to measure them. This is the atomic mass unit (amu). Atoms are almost entirely empty space. If the nucleus were the size of a basketball, the first electrons would be somewhere near Springfield.
Model of an Atom The central part of the atom is called the nucleus. The nucleus contains positively charged protons that weigh 1 atomic mass unit. The nucleus also contains neutrons that have no charge and weigh 1 atomic mass unit. Electrons are extremely small units of an atom that have a negative charge and move around the atom in orbits. Protons and electrons stay together because they attract each other. + O -
Model of an Atom Electron Proton Neutron
Nucleus The nucleus is where the protons and neutrons are located within the atom.
Atomic Number The atomic number of an atom is the number of protons it has. If an atom has 6 protons, it is carbon. It does not matter what else it has, if it has 6 protons then it is carbon.
Practice Number of Protons
Electron Cloud The electron cloud is the region around the nucleus occupied by electrons. Atoms are much, much denser near the nucleus.
Electrons Electrons are also arranged in shells. The first shell can hold a maximum of 2 electrons. All other shells can hold up to 8 electrons.
Valence Electrons The outermost shell of an atom is called the valence shell.
Protons and Electrons In an ATOM the number of electrons should always equal the number of protons.
Isotopes An Isotope is when an atom has a different number of protons and neutrons. Most elements have many different isotopes. This makes the nucleus unstable or radioactive in many cases.
Writing Isotopes To describe an atom, write the name of the atom and then write the total number of protons and neutrons that are found in it’s nucleus. The total number of protons and neutrons in the nucleus is called the Mass Number.
Isotopes and Mass Number
Abbreviating Mass Number To abbreviate mass number, write the symbol of the atom and then to the upper left write the mass number and under that, write the atomic number.
Index Atoms and Elements Chemistry Unit 02 Honors Unit 02 Module 03: The Structure of Atoms1 Based on the PowerPoints by Kevin Boudreux.
5 Departure and arrival atoms10 ... characters describing the structure of the molecule according to the rules which are described in ... For ChemFig ...
How Atoms Work. by ... What are the basic structure and the atomic number of an atom? How does the photoelectric effect support the particle theory of light?
1.CHAPTER 5 Atomic Structure© 2013 Marshall Cavendish ... 5.2 The Proton Number and Nucleon Number 5.3 Isotopes 5.4 Arrangement of Electrons in Atoms10.
The structure and spectra ofhydrogenic atoms10.1 The structure of hydrogenicatoms10.2 Atomic orbitals and theirenergies10.3 Spectroscopic transitions ...
The diameter of an atom for this type of hydrogen differs from the more common type. Atoms vary greatly in weight, but they are all about the same size.
The structure has been determined from three-dimensional X-ray data collected by ... The scattering factors used were those for neutral atoms10, ...
J.J. Thomson circumvented Earnshaw's prohibition on structure by postulating a "plum-pudding" atom. When Rutherford showed that the nucleus was a point, ...