400 BC Democritus: He hypothesized that all matter (plus space and time) is composed of tiny indestructible units‚ called atoms. Democritus performed no experiments. 1 .All matter consists of invisible particles called atoms. 2. Atoms are indestructible. 3. Atoms are solid but invisible. 4. Atoms are homogenous. 5. Atoms differ in size‚ shape‚ mass‚ position‚ and arrangement. ->Solids are made of small‚ pointy atoms. ->Liquids are made of large‚ round atoms. ->Oils are made of very fine
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THE VSEPR THEORY The VSEPR stands for ¡°Valence Shell Electron Pair Repulsion¡±‚ the theory is used for predicting the structure of molecules. The theory can be used in two main steps. First‚ the number of all bonding pairs and lone pairs is calculated‚ next‚ these pairs of electrons are rearranged in order to minimize the repulsion between them. Different number of bonding pairs and lone pairs of electrons can form different structure. When there are only two bonding pairs around the central
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subatomic particles that play the greatest role in cellular chemical reactions are electrons. protons. neutrons. isotopes. 0 out of 5 The correct answer is: electrons. Question 2 of 20 The structural unit that retains the properties of an element is the molecule. atom. cell. electron. 5 out of 5 Correct!! Question 3 of 20 Which of the following are found in the nucleus of an atom? Protons Neutrons Electrons A and B 0 out of 5 The correct answer is: A and B Question 4 of 20 The component
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electricity is the electric current resulting from the existence of charged particles such as electrons or protons. Electricity figures everywhere in our lives. Electricity lights up our homes‚ cooks our food‚ powers our computers‚ television sets‚ and other electronic devices. Electricity from batteries keeps our cars running and makes our flashlights shine in the dark. Here’s something you can do to see the importance of electricity. Take a walk through your school‚ house or apartment and write
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Describe the difference between a mixture and a compound. A compound is a substance in which atoms of different elements are chemically held to one another. A mixture is a substance made by combining two or more different materials in such a way that no chemical reaction occurs. A mixture can usually be separated back into its original components‚ a compound cannot. Below are some examples of the differences between each. Compounds •Compounds are pure substances. •They are made up of two or more
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metals do not conduct electricity quite as good as copper. The electrons of different types of atoms have different degrees of freedom to move around. With some types of materials‚ such as metals‚ the outermost electrons in the atoms are so loosely bound that they chaotically move in the space between the atoms of that material by nothing more than the influence of room-temperature heat energy. Because these virtually unbound electrons are free to leave their respective atoms and float around in the
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poor conductor of electricity. If the electrons in an atom can’t be moved from their orbits at all‚ the material is an insulator. If at least some of the electrons can be moved‚ the material is a resistor. Two of the best-known conductors of electricity are silver and copper. The atomic structures of the silver and copper atom are compared in Figure 6. Note that both atoms have only one electron in the outermost orbit. This makes silver and copper excellent conductors of electricity. Silver
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c. Insulator • Number of valence electrons is 1-3 with very high conductivity • Number of valence electrons is 4 with intermediate conductivity • Number of valence electrons is 5-8 with very low conductivity Semiconductor Conductors • Has more electrons that are free to move • Supports charge carriers to flow • Support flow of electricity • Has very low resistance allowing easy flow of electron current • Has less than 4 valence electrons – Examples: metals‚ electrolytes and
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CONTENT Contents IONIC BOND 2 METALLIC BOND 9 The "Sea of Electrons" Theory 14 Conductors‚ Insulators and Semiconductors 16 25 IONIC BOND Ionic bond is formed when electron transferred from a valence shell of an atom to the valence shell of another atom. Ionic bond involves electron transfer across two atoms. The atom which donates the electron is called cation which is a positive ion whereas the atom which gains the electron is called anion which is a negative ion. The opposite charge
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that scientists use as a premise for almost every study. The kind of atoms is the first one that the material is made up of. You will have your neutral elements and your compound elements. The neutral elements have the same amount of protons and electrons‚ which basically cancel each other out leaving them neutral. The compound element deals with combining more than one element. In the way those atoms are arrange is the second one. The best example of this is by comparing the atoms of liquid and the
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